Improved Methods for Clearance Testing and Visual ... · 5. To prepare a draft MDHS on clearance sampling and testing and publish results. Main Findings 1. Laboratory investigations

Broad Lane, Sheffield, S3 7HQTelephone:+44 (0)114 289 2000Facsimile: +44 (0)114 289 2500

HEALTH AND SAFETY LABORATORYAn agency of the Health and Safety Executive

© Crown copyright 2001

Improved Methods for Clearance Testing andVisual Assessment of Asbestos Removal

Operations.

HSL/2001/11

Environmental Measurement Group

Mr Peter R Stacey MRSC CChem and Dr G Burdett

Dr G BurdettProject Leader:

Summary

Objectives

1. To further develop and define a standardised method for visual clearance and for disturbance (oraggressive) sampling inside the enclosure and after the site has been vacated.

2. To research and test a surface sampling method (by PCM and TEM) to collect surface dust as ameasure of site cleanliness after a removal operation.

3. To investigate the current standard of visual clearance being carried out after asbestos removaland to document findings to inform and provide future guidance and training.

4. To assess any residual levels of asbestos remaining after the contractor has left by carrying outdisturbance sampling before reoccupation and/or surface sampling.

5. To prepare a draft MDHS on clearance sampling and testing and publish results.

Main Findings

1. Laboratory investigations to determine the detection limit of simple visual wipe tests, atorch test and quantitative assessment of surface fibre sampling methods wereundertaken before evaluating them in a field survey. A laboratory investigation of theability of different dust raising methods was also carried out along with measurements ofthe settlement rates and decline of asbestos concentrations with time.

2. A total of 20 site visits were made. Fifteen sites had enclosures still intact and clearanceassessments were carried out. At two large sites, an additional visit was made to asecond enclosure, making a total of 17 clearance assessments. Due to the difficulty inarriving at the start of the clearance, it was only possible to observe the site analystsclearance procedure at 11 of the 15 sites. A total of 12 clearances involving 11different analysts from 6 different laboratories were observed. The removal sites variedin size from a small boiler room to a large multi-story car park. A range of materials hadbeen removed: 4 sites involved the removal of ceiling tiles, 3 sites involved the removalof lagging, 4 sites involved the removal of AIB board and 5 sites involved the removalof sprayed asbestos.

Experimental observations on surface tests

3. Wipe tests based on the density of the deposit and colouration of the wipe media bythe surface dust were found to be a simple way to estimate whether surface dust levelsare likely to present a problem and whether the site has been adequately cleaned.


4. The likely lower level of detection for aluminium oxide and amosite was measured inlaboratory trials on different wipe media. The Whatman 540 filters and Mediwipeswere found to give a visible contamination line after a 10 cm wipe at aluminium oxideparticle concentrations of about 200 p/mm2 and at amosite concentrations of 60 f/mm2.

5. The wipe test appeared too sensitive for the current levels of cleaning in UKenclosures as 94 % of enclosures failed the wipe test. However, a similar percentagefailed HSL’s clearance air monitoring.

6. Although it was not envisaged that the project examine methods of cleaning,observations of working practices employed in enclosures suggest that the mostcommon methods employed; vacuuming and wet mopping are not very effective or arenot applied effectively.

7. The HSL operator found the HSL low angle of incidence torch test very useful todetect surface dust but could only be used on smooth surfaces. However, differentoperators are not consistent with their approach or judgments.

8. Adhesive tape was found to be a simple method to sample surface dust and phasecontrast microscopy could be used to quantify the amount of asbestos fibres on thesurfaces. Adhesive tapes can also be treated to allow further analysis by SEM or PLMto identify the fibres present. It does not, however, work well on rough or dampsurfaces.

9. Forensic tape produces a clearer mount than adhesive tape for PCM analysis.However, it is limited, if further identification of fibres is required.

10. Forensic tape was found to be the most versatile and efficient sampling medium over arange of surface types.

11. Micro-vacuuming in the simplified form used, was found to be less efficient than tapesampling but gave a more integrated sample, as larger areas or multiple areas could besampled.

12. A concentration of fibres on a surface of 100 f/mm2, determined using forensic tape,produced a concentration in air of about 0.01 fibres/ml, when an area of about 50 m2

was brushed with a hand brush for 5 minutes. This means that the visual wipe test whichcan detect down to 60 f/mm2 of amosite will have the potential sensitivity to detectsurface dust levels which may fail the clearance air monitoring.

13. The surface tests can only provide an indicator of the likely outcome as chrysotileasbestos will not discolour a white wipe media while other dust particles will. It shouldalso be noted that the efficiency of surface sampling is dependent on the type ofsurface and the sampling media used. Also, the small areas sampled may not berepresentative of other areas.


Experimental observations on disturbance / resuspension of surfacedusts and asbestos fibres

14. A survey identified that the most common method of disturbing dust in the enclosureswas to shake a plastic bag in the air or to fill a plastic bag with air and hit it against thewalls. These practices were shown in laboratory tests, to be very ineffective methods ofdust disturbance (less than one tenth compared to brushing).

15. Leaf blower’s were found in experimental comparisons to be the most efficienttechnique for resuspending and mixing settled dust, and were some 4-5 times moreefficient than brushing.

16. The effectiveness of a leaf blower will dependent on the outlet velocity and the distancebetween the outlet nozzle and the surface. Leaf blowers also generally require anelectrical supply inside the enclosure.

17. The efficiency of the leaf blower may mean that surface dust levels which may not bedetected by a simple visual wipe test, may fail the clearance air monitoring. Also atsome of the enclosures sampled in the survey, the airborne levels produced if a leafblower had been used, would have been likely to exceed the control limit and will putclearance assessors at increased risk, as the respirators they use have low protectionfactors.

18. Brushing is also an effective method of resuspending the dust from the surface but itdoes not mix and disperse the particles as efficiently as a leaf blower.

19. Experiments with ground amosite asbestos and resuspension of the fibres with a leafblower indicate that 40 % of asbestos fibres settle out in the first 60 minutes. With handbrushing, there was a sharper decline in the airborne concentration of amosite fibres,which had halved after about 10 minutes and over 90% of the airborne fibres hadsettled out within 30 minutes after disturbance.

20. The additional mixing action of the leaf blower had an important influence on the airmeasurements as the fibres lofted by the leaf blower took longer to settle out. Thisobservation alone accounted for most of the difference between the relative efficienciesof brushing and leaf blowing.

21. This also suggests that for brushing, the sampling period should be short (30 minutes orless), or the surfaces should be subject to more frequent disturbance (e.g. every 15minutes instead of every hour). Alternatively, fans could be used to further mix anddistribute the dust in the air.


Field observations on visual assessment by site analysts

22. In most cases the analyst was involved in a remedial cleaning process rather than aseparate visual clearance assessment.

23. The role of the analyst in the clearance process is ambiguous and they need arecognised independent role without any financial relationship with the removalcontractor. At some sites visited the analytical firm did have a supervisory role.

24. Sites where the analyst had a recognised supervisory role, generally allowed a period oftime for the enclosure to dry, before starting the clearance assessment. Analystscontracted by the removal contractor usually had less chance to do this and would waita limited period (~1 hour) and start clearance when still damp or wet.

25. The spraying of the PVA was only observed at few of the sites and generally allequipment and surfaces which were to be removed or disposed of were liberallysprayed by the removal contractor.

26. There was however considerable variation in when the PVA spraying took place. Oftenthis occurred before the clearance assessment and sometimes additional spraying tookplace after the visual assessment.

27. Analysts would often perform the visual assessment using a torch but were used only tohelp find relatively large pieces of debris and were not used to assess whether therewas a fine layer of dust on the surfaces.

28. Two of the 17 enclosures observed failed the site analyst’s visual assessment becauseof macro contamination with asbestos. One site had several failures before it was finallypassed.

Field observations on visual assessment by HSL analysts

29. Two thirds of enclosures did not use any covers on the floors which meant they werereadily contaminated.

30. Some of the uncovered floors consisted of concrete, whose rough surface would makeit almost impossible to clean up fine asbestos dust.

31. All but one of the floors of the enclosures were left visibly dirty with dust (asdetermined using a simple wipe test and low angle torch test) but nearly all had passedthe visual assessment by the site analyst.

32. Many sites had sprayed the enclosure with PVA before the visual assessment, makingthe recognition of fine debris and dust more difficult.


33. Glass fibre insulation was left in place inside several enclosures. Potentially this glassfibre was contaminated, as it was left uncovered and it should have been removed atthe same time as the asbestos. It also makes the analysts position more difficult as theydo not disturb this material because it will produce fibres if disturbed during the air test.

34. Over half of the enclosures were found by the HSL analyst to be either wet (29%) ordamp (24%). Often this was due to the liberal spraying of PVA solution before theclearance assessment and insufficient time being given for the enclosure to dry.

Field observations on clearance air monitoring by site analysts.

35. All analysts disturbed the enclosure area for 5 minutes, regardless of the size of theenclosure. This made the method less sensitive for larger enclosures.

36. At some sites the enclosures consisted of several rooms. Again this made the methodless effective as the air movement will be restricted and the disturbance time in eachroom reduced.

37. Two of the 16 enclosures failed clearance air monitoring on the first attempt, both ofthese passed on the second attempt.

38. Site analysts used a removal sack as the disturbance method in 10 of the 16 (63%)enclosures where clearance air monitoring was observed.

39. Of the 12 clearances assessments observed only at four was the floor of the enclosuredeliberately disturbed, in spite of the fact that this is the obvious place for fine asbestosfibres and debris to collect. At the four sites where the floor was disturbed, this wasdone using an inflated plastic bag, where the amount of contact and the resuspensionaction is likely to be low. Only at two of these four sites was any serious attempt madeto disturb the floor.

Field observations on concurrent clearance air monitoring by HSLanalysts.

40. The results from the concurrent samples were analysed off site at HSL. Only 7 of the11 sites (64 %) and 8 of the 12 enclosures (67 %) monitored concurrently, would havepassed the clearance air monitoring according to the HSL fibre counting results. Of the33 samples taken and analysed by HSL only about half (17/33 or 52%) were found tobe below the 0.01 f/ml clearance indicator.

41. The one site failed by the site analyst, also gave the highest fibre concentrations in theHSL analysis (0.06 - 0.07 f/ml). There was a consistent bias in that the site analystsresults were lower than HSL’s. This bias was particularly significant in deciding whether


the site had passed or failed, and the percentage of samples recording fibre counts of<0.01 f/ml fell from >95% for site analyst samples to 52% for HSL concurrentsamples.

Field observations on clearance air monitoring by HSL analysts.

42. HSL carried out clearance air monitoring and disturbance at 14 of the 15 sites. One sitewas visually contaminated so was not sampled and one site produced such high levelsof airborne particles, the filters were uncountable.

43. Only one of the sites passed the clearance assessment based on the HSL disturbanceand clearance air monitoring. The site in question was very wet and had anunderground spring which covered the floor with water.

44. Of the 53 individual air samples analysed 43 (80%) were > 0.01 f/ml. The averageconcentration inside the enclosures during clearance sampling was 0.068 f/ml with arange of 0.23 to 0.0002 f/ml. The average air volume sampled was 306 L with amaximum of 600L and a minimum of 100L. These air volumes were lower than therecommended minimum of 480L due to the logistic problem of the Contractor wantingto take down the enclosure as soon as the site analyst cleared the site.

Field observations on removal of enclosures / post clearance

45. Workers are often provided with paper masks 8810 type FFP2S with a protectionfactor of 10. However, many do not wear them when desheeting and some workerswill break to smoke a cigarette whilst in the old enclosure area.

46. TWA personal exposures of about 0.1 f/ml were obtained from workers desheetinglarge enclosures. This work activity is probably when the removal workers are exposedto their highest levels of fibres since whilst removing the asbestos they would have beenprotected with powered respirators with high efficiency filters.

47. Post clearance visits were made to three sites. Two sites had visibleasbestos-containing debris left after the site had been cleared and the enclosureremoved. All sites were visibly dirty or very dirty based on a visual inspection. One sitehad a room full of the removed non-asbestos panelling.

48. Post clearance air monitoring was carried out at the site without visible asbestos debrisand gave values of up to 0.08 f/ml with brushing.

49. Another HSL/HSE survey conducted at the same time as this report found visibleasbestos debris at three of the six sites visited.


50. This suggests that no effective pre-cleaning takes place before the enclosure isconstructed, and/or that no post-cleaning takes place after the enclosure is removed.

Main Recommendations

1. Different HSE documents should be updated to be more consistent and use the sameterminology.

2. It is suggested that the terms ”clearance assessment”, involving a “visual assessment”and “clearance air monitoring” are used in future HSE documents.

3. More attention should be given to the detection and clean up of fine settled dust,including:

i. Clearance visual assessments should involve a simple standard wipe test to detectthe concentration of fine settled dust;

ii.A standard method for tape sampling to measure the concentration of fibresremoved from surfaces should be developed for field use by analysts so they canestimate if high airborne concentrations are likely to be produced during clearance airmonitoring;

iii.Guidance on how to use low angle light beams to detect fine dust should be given byHSE.

4. A stronger message and attention needs to be given, that the entire enclosure should bedry before commencing a clearance assessment, including:

i. The visual assessment should assess and record any areas of the enclosure whichwere damp or wet;

ii.The ACoP states that enclosure should be, “as dry as reasonably practicable” whichis interpreted as it does have to be completely dry. Allowing a suitable time for it todry and the importance of this should be stressed in the ACoP and guidance;

iii.The clearance certificate should state whether the enclosure was dry at the time ofthe clearance assessment.

5. The clearance air monitoring needs to be much more standardised:

i. A standard disturbance should be specified based on brushing/sweeping (if a leafblower is deemed unacceptable);

ii.The time of disturbance should be adjusted to the size of the enclosure;


iii.Five minutes should be used as a minimum disturbance time for enclosures with areasof less than 100 m2 , a further 5 minutes or part thereof should be added for eachadditional 100 m2 up to a maximum of 15 minutes;

iv.The floor of the enclosure and other flat horizontal surfaces should be disturbed forat least half of the disturbance period and the surfaces which formerly had asbestosmaterials attached should be disturbed for at least a quarter of the disturbanceperiod.

6. All floors and surfaces should be pre-cleaned before the enclosure is established andthen covered to protect them from further contamination. This covering could then beremoved and the air test performed on the remaining surfaces which, in theory, shouldnot be contaminated. Most sites would probably pass the air test if this simple measurewas implemented to prevent the spread of asbestos.

7. The site analyst should be more independent from the asbestos contractor and shouldbe employed by the client.

8. Current guidelines on the use of PVA are not being followed and are consideredimpracticable. A change in guidance is necessary. This is also important in obtaining dryenclosures.

9. Use of critical barriers and a double skin of polythene should be encouraged. This willallow the contaminated polythene to be locked down and removed before anyclearance test takes place.

10. Guidance on enclosure removal should stress the risk of exposure due to residualcontamination.

11. Hygiene units should be functional until the clearance certificate has been issued.

12. Materials which are likely to be contaminated with asbestos and cannot be coveredshould be removed.

13. A post-clearance assessment should be carried out after the enclosure has beenremoved but with the critical barriers still in place.


Contents

307.3. HSL clearance airmonitoring results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

287.2. HSL concurrent results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .287.1. Site analyst results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

7. RESULTS OF THECLEARANCE AIR MONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

276.3. Vacuum, filter swab andtapes samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

276.2. Low angle torch test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266.1. Wipe samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

6. FIELD EXPERIENCE WITHTHE SURFACE SAMPLINGMETHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

255.4. Clearance air sampling byanalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

235.3. Observations inside theenclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23

5.2. Personal protectiveequipment anddecontamination procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

225.1. Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

5. SITE VISITS ANDOBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

214.2. HSL clearance airmonitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

174.1. Tests for surfacecontamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

174. FIELD TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

3.3. Experiment 3:- Monitoringof settling in ‘real time’ usingFC2 Fibrecheck monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

113.2. Settling time of disturbedfibres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

83.1. Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

3. EFFECTIVENESS OFDISTURBANCE METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

82.2. Experimental Trials withasbestos fibres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22.1. Quantitative evaluation ofthe detection limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22. LABORATORY EVALUATIONOF WIPE SAMPLING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


51A1.2. Inspector, contractor,client relationships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51A1.1. Problems with the currentadvice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51A1. APPENDIX 1: CRITIQUE OF

CURRENT CLEARANCE PRACTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4512. REFERENCES FOR THE

REPORT AND APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4311. RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

10.8. Field Observations:removal of enclosures / postclearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

42

10.7. Field Observations:Clearance air monitoring byHSL analysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

42

10.6. Field Observations:Concurrent clearance airmonitoring by HSL analysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

41

10.5. Field Observations:Clearance air monitoring by siteanalysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4110.4. Field Observations: VisualAssessment by HSL analysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4010.3. Field Observations: VisualAssessment by site analysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

40

10.2. Experimental observationson: Disturbance / resuspensionof surface dusts and asbestosfibres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3910.1. Experimental observationson: Surface tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3910. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

9. VISITS TO PREMISES AFTERCLEARANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37

8. PERSONAL EXPOSUREWHEN REMOVINGENCLOSURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35

7.5. Relationship between Surface Sampling Techniqueand Air Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

347.4. Reasons for differencesbetween HSL and field analysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


76A5.1. Types of method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

A5. APPENDIX 5: REVIEW OFSURFACE DUST SAMPLING METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

74A4.6. Post - ClearanceReassurance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

73A4.5. Time of sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

A4.4. Effectiveness of dustdisturbance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

72A4.3. Methods of dustdisturbance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

69A4.2. Site studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

A4.1. Review of currentregulatory methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

68

A4. APPENDIX 4: LITERATUREREVIEW OF CLEARANCE AIRMONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67A3.7. Other guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66A3.6. Completeness of clean-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66

A3.5. Completeness of theremoval and clean-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

65A3.4. Inside enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64A3.3. Project work performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

A3.2. Extent of ACM within thescope of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

63A3.1. ASTM Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

A3. APPENDIX 3: LITERATUREREVIEW OF VISUAL ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

60A2.8. Recommendations forchanges in HSE advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59

A2.7. Assessment of HSEadvice on clearanceassessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59A2.6. MDHS 87 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57A2.5. MDHS 39/4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

A2.4. Guidance on clearancetesting EH51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

56A2.3. Guidance on clearancetesting EH10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

54A2.2. ACoP Procedure for siteclearance testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53A2.1. CAWR (amended 1999) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

A2. APPENDIX 2: REVIEW OFCURRENT HSE REGULATIONS,ADVICE AND GUIDANCE ONCLEARANCE ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

A7. APPENDIX 7: SUGGESTED NEWTEXT FOR REGULATIONS, ACOP ANDGUIDANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

96 Site R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96Site Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

USE OF WIPE TESTS ININCIDENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

95Site P (Post removalinvestigation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

93A6.15. Site O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90A6.14. Site N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89A6.13. Site M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88A6.12. Site L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86A6.11. Site K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85A6.10. Site J . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84A6.9. Site I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84A6.8. Site H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83A6.7. Site G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83A6.6. Site F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82A6.5. Site E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81A6.4. Site D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81A6.3. Site C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80A6.2. Site B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80A6.1. Site A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

A6. APPENDIX 6: SITESAMPLING ANDOBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

79A5.6. Recommended methodsfor surface dust sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

78A5.5. Quantitative asbestosspecific methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

78A5.4. Whole surface analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

A5.3. Quantitative investigation -radioactive assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

76A5.2. Sampling variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



1

1. INTRODUCTION

Current HSE advice in the Approved Code of Practice (ACoP) for work with asbestos insulation,asbestos coating and asbestos insulation board (HSC, L28) refers to site clearance testing as anassessment at the end of a removal to check that the area is fit to be returned to normal occupation.It is described as a two stage process: clearance visual inspection and clearance air monitoring. Theresponsibility for the clearance is placed on the employer of those who carried out the work (usuallythe asbestos removal contractor). They must ensure that the enclosure or work area and immediatesurrounding area is thoroughly cleaned and that, “A thorough visual inspection of these areas shouldbe carried out to make sure that all visible traces of asbestos have been removed as far as reasona-bly practical from the enclosure and the surrounding area.”

Once the work area and immediate surrounding areas have passed a visual inspection, clearance airmonitoring is carried out to check that the concentrations of airborne fibres remaining in the areasaffected by the work is as low as reasonably practicable. The clearance air monitoring should beaccompanied by activities which raise dusts from the surfaces, at least to a level consistent withnormal use of the area and possible future work activities. In most cases it is reasonably practicableto clean the work area thoroughly enough for the airborne fibre concentration in the work area afterthe final cleaning to be less than 0.01 f/ml when measured by methods set out in separate HSEguidance (i.e.MDHS 39/4).

This report gives the results of project R51 171 which was commissioned by HSE to investigate thecurrent practices and to develop improved methods for clearance testing and visual assessment ofasbestos removal operations. The project had five objectives:

1. to further develop and define a standardised method for visual clearance and fordisturbance (or aggressive) sampling inside the enclosure (and after the site has beenvacated);

2. to research and test a surface sampling method (by PCM and TEM) to collect surfacedust as a measure of site cleanliness after a removal operation;

3. to investigate the current standard of visual clearance being carried out after asbestosremoval and to document findings to inform and provide future guidance and training;

4. to assess any residual levels of asbestos remaining after the contractor has left by carry-ing out disturbance sampling before reoccupation and/or surface sampling;

5. to prepare a draft MDHS on clearance sampling and testing and publish results.

The first four are addressed by this report.

As part of the initial work a number of literature searches and reviews were carried out and thesehave been appended to this report. A critique of the current UK asbestos clearance practice was


2

carried out in appendix 1, with a review of HSE’s published guidance in appendix 2. Appendix 3reviews clearance practices in other countries. A literature search and review of visual assessmentand clearance air monitoring methods is given in appendices 4 & 5 and a review of surface dustsampling is given in appendix 6. These reviews are important as they put the research work under-taken in the main report in context. Appendix 7 outlines the suggested changes that are necessary toupdate the regulations, approved code of practices and guidance, based on the outcome of thework.

Investigations on the detection limit and qualitative performance of simple visual assessment testswere undertaken in the laboratory. Quantitative assessments of the efficiency of surface fibresampling methods and different dust raising methods were also carried out in the laboratory, alongwith measurements of the settlement rates and the decline of asbestos concentrations with time.Several of these methods were then tested in a field survey, which was also designed to observecurrent clearance practices used by site analysts. A total of 20 site visits were made.

The results of the reviews, laboratory studies and field surveys are discussed and used to drawconclusions and recommendations for future clearance practice.

2. LABORATORY EVALUATION OF WIPE SAMPLING.

Visual assessment of wipe samples provides a simple way to check whether the surfaces have beenadequately cleaned. The presence of any visible dust on surfaces would suggest that the clean up hasnot been adequate but the sensitivity of the tests are important to see how low a concentration ofdust can be detected and how method-dependent the limit of detection is. Dust colour will be amajor factor in any wipe test and a predominantly white dust will not be detected by a white testmedia but a black dust will have a much lower limit of detection. For the laboratory evaluation amedium colour dust was chosen, similar to amosite asbestos and somewhat lighter than ordinaryhouse dust. Particle size is also important and it is assumed that high efficiency particle arresting(HEAP) vacuuming would have been carried out and this would have removed most of the largerparticles but have left many small particles which are likely to be bound more tightly to surfaces by Van der Waals attractive forces. Finally, surface type will also affect the sampling media so the testswere carried out on what is the most commonly found and extensive type of surface - polythene.

2.1. Quantitative evaluation of the detection limit.

2.1.1. Experimental design

The efficiency of each material tested was assessed by settling a non fibrous powder on a 1000gauge polythene sheet (the most common material found in enclosures). The particulate material usedin all tests, was F1200 grade aluminium oxide grinding power ‘Aloxite’ which had a similar colour asUICC* Amosite asbestos (Figure 1). The ‘Aloxite’ powder is shown in the bottom left segment andthe UICC amosite in bottom right tray. The powders in the two top trays are UICC chrysotile andUICC crocidolite.

* Union International Contre le Cancer


3

Photo removed to reduce file size

Fig 1: Colour comparison between ‘Aloxite’ and common asbestos dusts

The mass median diameter of the F1200 Aloxite was 4.5 µm and the mass median aerodynamicdiameter 8.6 µm. Figure 2 shows the distribution of the particle size in terms of cumulative volumeand indicates that about 80 % of particles, by volume, had a size of less than 5 µm in diameter. Thesheeting was placed onto a 0.5 m2 wooden board painted black that was segmented into 10 cm2

areas with white lines. This was then placed into a rotating wheel in the lower of the two chambers ofa dust box (Figure 3).


4

Fig 2: Per cent % Cumulative Volume Of Aloxite Powder

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

Particle size (µm)

Per

cen

t C

um

mu

lati

ve V

olu

me

Figure 3: Diagram of dust generation apparatus

Compressed air injector

Impactor

Upper chamber

Air straightners

Test surface

Turn table

Air drawn through apparatus

The dust was sucked into the top section of the dust box from a rotating plate using a compressed air


5

injector. Any large agglomerates were removed by impacting the entrained particles onto a plateplaced 5 - 6 cm in front of the inlet nozzle. The dust was dispersed in the upper chamber and drawnthrough a set of air straighteners into the main section of the dust box, before settling onto thepolythene sheet. The distance from the impactor to the sample surface was approximately 2m.

2.1.2. Measurement of surface loading.

The surface loading was measured in two ways. Firstly, nine pre-weighed, 47 mm diameter (18.1cm2 ) aluminium foil impactors were placed on the polythene surface before the Aloxite dust wasgenerated and their increase in weight recorded. Secondly, nine 25 mm mixed cellulose ester griddedfilters were placed alongside the foils before loading and the number of particles on the filterscounted after the surface was loaded with dust. Figure 4 showed there was an approximate linearrelationship between the average weight change recorded on the foils and the average number ofparticles counted by x500 phase contrast microscopy on the same number of filters.

Fig 4: Comparision between average particles / cm2 counted and average weight on metal foil

y = 7E+06x - 10019R2 = 0.8726

0

50000

100000

150000

200000

250000

300000

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045

Average change in weight of foil mg/cm2

Ave

rag

e p

arti

cles

/ cm

2

The counting technique was used by itself for surfaces where the weight change on the metal foil was less than 0.1 mg.

Figure 5, below shows the variation of the particle counts on the filters placed at different areas onthe sheet with each surface loading over the polythene sheet.


6

Fig 5:- Variation of counted particles/cm2 with sampling run

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

3 4 5 6 7 8 9 10 11 12 13

Sampling Run Number

Co

un

ted

par

ticl

es/c

m2

DataAverage Count

At the lower loadings the variation in particles counted / cm2 is about 22 - 28 % RSD for about 95.5% of the data. At the highest loadings the counting was more variable and ranged from about 50 - 80% RSD. The mass recorded on the foils showed that variations across the sheet were lower at thehigher loading, than shown by the particle counts. Part of the increased variability was due to the hotacetone mounting method appeared to disturb the particle distribution on the filters and a smallernumber of fields were counted when higher loadings were present.

2.1.3. Wipe testing

Four different wipe media were chosen, either as they were used previously for wipe sampling or arereadily available for use. These were:

w 7 cm diameter Whatman 540 cellulose filters,

w ‘Medi-Swab’ swabs containing 70 % v/v isopropyl alcohol medical wipes,

w baby wipes and

w tissue paper.

The damp or wetted material was rolled around a hexagonal shaped pencil and run once, along thesurface in one direction along one side of a 10 cm grid outlined on the board behind the plasticsheeting. The material was then unrolled and illuminated with a light from behind. A torch was alsoshone at the surface of the polythene at an acute angle in order to assess if particles were visible bythis method. Three repeat sampling exercises were made on each surface with each wipe material.

2.1.4. Results and discussion

Material that possess a more rigid structure such as the Whatman filters and medical wipes werefound to be more sensitive to detecting particles on the surface than the baby wipes or tissue paper.


7

This was because the dust accumulated along a narrower area of the filter surface and the greaterdensity of particles was more visible. A line was only faintly visible with these medium when thesurface had a average concentration of 15700 with estimated upper and lower 95.5 % confidencelimits of 18600 and 12900 assuming a Poisson counting distribution. The line was easier to observeon the filters when they had ‘dried’ out. The medical swabs dried quickest as they contain iso-propylalcohol, while the Whatman filters, saturated with water, took 5 - 10 minutes. Table 1 compares theparticle counts on the mixed cellulose ester filters with the visual detection of dust on various wipemedia.

√5,608√8,045√√√15,678√√√21,368√√√28,065√√√39,387√√√62,152√√√√√63,290√√√√√76,473√√√√√127,400√√√√√226,454√√√√√241,142√√√√√254,738

TorchFilter PaperMedi-swabs

TissuePaper

BabyWipes

Average ConcentrationParticles/cm2

Table 1: Results from tests with wipe material

This experiment was repeated and the surface loading evaluated using transparent forensic tape asthe collection medium to estimate the density of the particles on the surface of the plastic. The advan-tage of the transparent forensic tape is that the particles deposited can be counted without anyfurther sample preparation which could disturb the particles. The results on a plastic surface at threedifferent concentration levels are shown in table 2 below.

15,587√21,899√27,024

Whatman Cellulose 540 Filters Average (of 9 filters) surface level Particles/cm2

Table 2: Repeat of experiment using average counts on transparent forensic tape.

Using this medium, the end point of detection for cellulose filter paper was re-estimated as approxi-mately 21899 particles/ cm2, (with estimated upper and lower 95.5 % confidence limits of 25112and 18556 particles/cm2, assuming a Poisson counting distribution). At this loading, a very thin andfaint grey line was only visible on the wipe material when it was completely dry. A much more visible


8

line was produced with the 27024 particles/cm2 loading (with estimated upper and lower 95.5 %confidence limits of 30320 and 23022 particles/cm2, assuming a Poisson counting distribution).

2.2. Experimental Trials with asbestos fibres

Ground amosite fibres were air dispersed using a leaf blower and allowed to settle out overnight ontoa polythene sheet on the floor of a test chamber measuring approximately 2.5 x 2.5 x 3 m. Usingforensic tape lift sampling, the average surface concentration of amosite fibres on the polythenesurface was found to be 2010 fibres/cm2 based on five samples taken at different locations on thefloor with a sample standard deviation of 500 fibres/cm2. Three separate single 10 cm wipes usingthe Whatman filters did not produce a visible line on the filter media. However, with multiple wipes afaint line was visible after the third wipe suggesting the detection limit of about 6000 fibres/cm2. Thelower detection limit for amosite fibres may be due in part to particle shape and surface area differ-ences but the surface tape samples showed that some small particles of non fibrous dusts had alsobeen suspended during the air dispersion and settled out with the asbestos. Therefore it appears thatasbestos can be evaluated by a single wipe test.

3. EFFECTIVENESS OF DISTURBANCE METHODS

The method of dust disturbance used by the analyst responsible for the assessment of clearance isnot specified in MDHS 39/4 and analysts are at liberty to use any they consider appropriate. It wasfound from the site clearance visits that the methods most commonly used were; shaking a emptyplastic bag, banging a large plastic bag full of air against surfaces, brushing a large plastic bag full ofair against flat surfaces, banging a clipboard against flat surfaces, brushing a clipboard against flatsurfaces, shaking a clipboard vigorously and brushing with a hand brush. The effectiveness of thesemethods may vary greatly and may not give a realistic estimate of potential asbestos levels that wouldbe produced by a more representative activity, (e.g. sweeping the floor with a broom or brush,vacuum cleaning or dusting). It is important that the test method is effective so that the levels ofasbestos fibres remaining on the site do not give rise to high airborne concentrations.

3.1. Experimental

The laboratory experiments were carried out in a test chamber measuring approximately 2.5 x 2.5 x3 m. The room has an air extraction facility, that was set to its lowest flow rate of 0.1 m/s (~ 0.5m3/minute extracted) during the first experiment and was shut off during subsequent experiments. A 3stage polythene air lock was built outside the entrance door to allow entry and exit to the chamberby an operator wearing full personal protective equipment. A glove port was used for some of theinside handling tasks. Two series of measurements were made to assess the different methods ofraising dust. The methods investigated were identified from a survey of clearance assessments. Also, a US method based on the use of a leaf blower was tested. The leaf blower chosen was a‘Black and Decker’ GW250 Mastervac 123 and has a claimed exit velocity from the blower nozzle 180 miles per hour (80 m.sec-1). By far the most common method of dust disturbance identified inthe survey was to bang a plastic bag full of air against surfaces.


9

Two air samples were collected at 8 L/minute over a 30 minute sampling period, which included thedisturbance activity. The shorter sampling time was used to minimise differences in the rate of falloutof fibres. One sample was collected at each end of the test chamber with the membrane filterpositioned face downwards in a conductive cowl about 1.5 m above the floor. The first set ofexperiments were made on the debris from the sawing of an board containing amosite. The floor areahad been HEPA vacuumed of any large pieces of debris remaining. For the second test amositefibres were dispersed in the chamber by blowing compressed air in a bowl containing the asbestos.In the first set of experiments the floor surface was disturbed for 5 minutes and in the second experi-ment for 2.5 minutes.

Fig 6:- Disurbance Experiment 1

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Shaking Empty Bag InAir

Hitting Surfaces withBag Filled with Air

Banging surfaces with aclipboard

Sweeping with HandBrush

Air

co

nce

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atio

n f

ibre

s/m

l


10


Results are given in figures 6 and 7. In the first experiment only banging the clipboard and brushingwith a hand brush recorded airborne levels of >0.01 f/ml. Sweeping with the hand brush recordedthe highest concentrations. In the second experiment the leaf blower appears most effective methodfor disturbing dust . However, this piece of equipment is relatively expensive, would requires a 240V electricity supply and cable and would need to be disposed of after use. As the air jet caused thepolythene covered floor to flex and bellow in a wave like manner, this may have produced a higherresult than would have occurred if the floor was not covered. Brushing was the next most effectivemethod followed by shaking a clipboard vigorously up and down at a surface. The shaking methodwould not be very practical when used in a very large area since it requires a lot of physical effort.Table 3 lists the methods tested in order of effectiveness relative to the brushing as this wasperformed in both experiments.

Counts below detection limitShaking empty plastic bag in the roomCounts below detection limitHitting surface with inflated plastic bag

0.14Brushing with a clipboard0.56Banging surfaces with a clipboard0.63Brushing with bag filled with air 0.75Shaking clipboard at surface (up and down)

1Sweeping with brush4.5Blowing air with a garden blower

RatioMethodTable 3: Order of effectiveness of disturbance methods


11

Fig 7:- Disturbance Experiment 2

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Shaking Clipboard BrushingClipboard

Brushing BagFilled with Air

Leaf Blower Sweeping withHand Brush

Air

Co

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ibre

s/m

l

3.2. Settling time of disturbed fibres

MDHS 39/4 requires a minimum sampling volume of 480 litres to be collect during clearance airmonitoring to achieve a limit of quantification (LOQ) of 0.01 fibres/ml. The LOQ, assumes 20 fibresis the upper 95 % confidence limit for the number of fibres significantly above the blank fibre levelrecorded in 200 fields. Typically pumps are often run at 8 l/min for one hour to sample minimumvolume of air required to achieve the LOQ.

3.2.1. Experiment 1

The rate of decline in airborne fibres was monitored in the test chamber using two pumps placed ateach end of the room ~1.5 m above the floor. The air extraction was switched off. The asbestoswas then disturbed by brushing with a hand brush for 5 minutes. Samples were taken, changing theheads on the 2 pumps every 10 minutes.

3.2.2. Results

The rate of decline of the fibres in air is shown in the figure 8 in terms of cumulative percent of fibrescollected on the sample filter at 10 minute intervals. In this experiment where brushing was used asthe disturbance method, 40 - 50 % of the fibres were collected in the first 10 minutes.

Fig 8: Cumlative Percentage of Fibres Collected In Experiment 1

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Sampling Time (minutes)

Per

cen

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f fi

bre

s

Figure 9 shows the measured concentration of asbestos fibres for each 10 minute sample.


12

10 15 20 25 30 35 40 45 50 55 60

Pump 2 ExperimentalPump 1 Experimental

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Air Concentration (Fibres/ml)

Time (minutes)

Fig 9: Experiment 1 Average Amosite Concentration compared with time

3.2.3. Experiment 2

A similar experiment was performed on a surface contaminated with amosite asbestos using the‘Black and Decker’ leaf blower, fig 10.

0 10 20 30 40 50 60

0

0.1

0.2

0.3

0.4

0.5

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0.9

1

Ave

rag

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on

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(f

ibre

s/m

l)

Time (minutes)

Fig: 10 minute Air Samples for Rate of Decline Using Leaf Blower


13

3.2.4. Discussion

The membrane filter sampling data shows that with hand brushing there was a sharp decline in thenumber of airborne amosite fibres and had halved in about 10 minutes and over 90% of the airbornefibres had settled out within the first 30 minutes after disturbance. This means that the last 30 minutesof the 1 hour sampling period was essentially reducing the fibre concentration estimated by about onehalf.

When a leaf blower was used to disturb the same fibres, a much lower rate of decline was found,with the airborne concentration of fibres only halving over 60 minutes. This shows that the methodof disturbance was not only important in determining the number of fibres made airborne, but alsohad a large influence on how long they stayed airborne. The experimental evidence suggests that theamount of mixing is also important and methods that give a good mixing action will better dispersethe fibres in the enclosure making a significant difference to the time taken to fall out. This factoralone was sufficient to explain an approximate factor of 5 difference between the hand brush andleaf blower over a 60 minute sampling period.

A field exercise in 1988, carried out by HSL in a building used as offices also showed a similareffect. In the previous exercise samples were taken every 30 minutes but the data does show a sharpfall in the original air concentration. (figure 11)

0 30 6192

124

PCM Results

TEM Results0

0.02

0.04

0.06

0.08

0.1

Average Air concentration

(fibres/ml)

Time (minutes)

Fig 11: Results from field experiment in 1988

PCM ResultsTEM Results

3.3. Experiment 3:- Monitoring of settling in ‘real time’ using FC2 Fibrecheckmonitor

The rate of decline was monitored using a real time fibre monitor the FC-2 Fibrecheck (HarleyScientific Instruments). This was connected to the test chamber through a sampling port 0.8 mabove the floor. Settled amosite dust was disturbed for 2 minutes using a leaf blower and in aseparate experiment for 5 minutes with a brush . A glove port was used to operate the blower fromoutside the room. The experiment was repeated twice at two different concentration levels with the


14

leaf blower. The FC2 Fibrecheck instrument is a continuous monitor which reports the cumulativeconcentration of fibres in air, so shows how the measured average concentration changes with time.Previous work (IR/L/MF/96/04) showed that there was a good linear relationship between themonitor and PCM counts for amosite fibre, with a small positive bias for the fibre monitor (slope =1.14).


Results are shown in figures 12 -14 and summarised in figure 15. The leaf blower was used to resus-pend fibres at two different surface concentrations. The cumulative air concentration v time wasmonitored with the FC-2 Fibrecheck instrument. The decay of the airborne concentration with timeafter the disturbance are shown in figures 12 and 13.

Fig 12:-Rate of Decline of Asbestos Fibres In Air When Disturbing the Air with a Garden Blower

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60 70 80

Time (Minutes)

Cu

mu

alti

ve F

ibre

s/m

l

Experiment 1Theoretical Decline

.


15

Fig 13:- Rate of Decline of Amosite Asbestos In Air After Disturbance with a Leaf Blower

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 10 20 30 40 50 60 70 80

Time (minutes)

Cu

mu

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on

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In A

ir (

f/m

l)

Experimental DataTheoretical Decline

The fibre raised by the second leaf blower test were allowed to settle out overnight beforere-disturbing by brushing horizontal and vertical surfaces for 5 minutes with a hand brush. Whenusing the same surface concentration the leaf blower was found to be more than 10 x efficient atdisturbing fibres (Fig 14) than brushing at these low concentrations.

Fig 14:- Comparision of the effectivness of the leaf blower with brushing

0

0.05

0.1

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0.2

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0.3

0.35

-5 5 15 25 35 45 55 65 75 85

Time (minutes)

Cu

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In A

ir (

f/m

l)

Leaf Blower 25 mins Brushing


16

Fig 15: Percent Decline of Amosite Asbestos Fibres Compared With Time from Disturbance

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

Time (minutes)

Per

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) o

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R

emai

nin

g

Leaf Blower 1Leaf Blower 2Brushing 5 mins

3.3.2. Discussion

The measured cumulative concentration with time with the leaf blower at two different concentrationsconfirmed the PCM assessments that this produces a much more well mixed sample which declinesrelatively slowly with sampling time and makes this much less of a variable.

Figure 15 shows the percentage decline in air of the original average airborne concentration andshows that the two experiments with leaf blowers had very similar rates of settling at two differentconcentration levels. The data suggests that when using a leaf blower the concentration in air ofamosite asbestos fibres is reduced by 13 - 16 % and 45 % in 60 minutes. Both curves for the leafblower experiments show a peak of asbestos concentration just after the disturbance has finishedwhich takes about 10 minutes to start to decline. This is probably due to the momentum of fibres inair turbulence as a consequence of the disturbance. The experiment for the disturbance by brushingconfirms the air sample results in the previous experiments. The decrease in air concentration isquicker with a reduction of about 55 % in the first 30 minutes and 71 % of fibres in 60 minutes. Thisrate of decrease for brushing would have implications for air sampling at low levels since it could notbe assumed that a significant proportion of fibres remain airborne for the whole 60 minute samplingperiod. If brushing were chosen as a standard procedure for disturbance then it would be moreeffective if fans were used to circulate the air to keep the fibres afloat.

The rate of decline has been compared with an empirical formula determined from observations onchrysotile asbestos levels in enclosures using TEM measurement. This empirical formula was derivedfrom only 8 single time points in eight different enclosures with different disturbance methods (Ewinget al., 1992). This predicted a rate of decline of chrysotile asbestos at any point in time is defined as

where x is the initial geometric mean airborne concentration, t is the settling time (in hours)y = x(1+t2)


17

and y is the airborne concentration after time t. The leaf blower mixing, gave a slower rate of declinethan found for chrysotile fibres even though it is a much thinner fibre and would be expected to stayairborne longer.

The measured decay curves in figure 15 were fitted with various models and it was found that asimple linear relationship described the decay curves for the leaf blower with gradients of 0.709 and0.625 with correlation coefficients (C.C.) of 0.99. The brush test was more variable due to the lowconcentrations being measured and gave a poor linear fit (C.C. 0.86) with a steeper gradient 0.948and was better described by an exponential fit (C.C. = 0.95). The results showed that the decaycurves are method dependent and it is wrong to assume a single equation can be used to predict thechange in fibre concentration with time.

The method of mixing of the air, as well as the method of dust disturbance, are both importantvariables when specifying the clearance air monitoring. Given the large differences between distur-bance methods it would seem important to specify a standard disturbance method.

4. FIELD TESTS

Seventeen clearance sites were visited during the project to test improved methods of assessing andquantifying surface contamination. The emphasis was to develop, test and compare practicalmethods

4.1. Tests for surface contamination

The literature survey showed that a wide range of tests both qualitative (visual) and quantitative havebeen used for surface contamination. In this study six different methods were tested for assessing thesurface fibre concentration; two visual and four quantitative tests. The quantitative tests used were allbased on readily available equipment that the analyst would have on-site or could easily bring to site.This means that phase contrast microscopy (PCM) evaluation is used for quantification of the surfacefibre concentrations, as this will be used for the clearance air monitoring. The counting rules inMDHS 59 should be used rather than in MDHS 39/4, as fibres may well be attached to particles insurface dust deposits and all fibres of respirable dimensions should be counted.

An effective test method should be able to detect or indicate a level of fibre concentration on thesurfaces that would fail clearance air monitoring. A practical test would save the removal contractortime and money, since clearance air monitoring failures may hold up the work for several hours andmore importantly result in missed deadlines and penalties. The advantages and disadvantages of eachtechnique are summarised in table 4 and the test protocols are described below.

4.1.1. Wipe test

The filter wipe test evaluated in section 2 was used at all sixteen sites. A Whatman 540 cellulose filterpaper was wetted with distilled water and rolled around a pencil. It was then drawn once for 10 cm


18

along the test surface. The filter was then examined by placing the back of the filter against a torchbeam to look for a visible line of dust.

4.1.2. Low angle torch/dust lamp test

A torch or preferably high powered dust lamp beam was shone along the surface at a low angle(grazing incidence) to illuminate surface dust particles. The angle should be as low as possible togive a long beam of light along the surface. This allows particles to be more easily observed by theshadows they cast and by the scattered light. This was found to be a very sensitive visual test in thelaboratory experiments with aloxite dust.

Torch

Illumination

Test surface

Particle

Shadow

Scattered Light

Fig 16: Low angle torch test

4.1.3. Micro vacuum sampling and PCM analysis

The equipment used for air sampling can be easily used to micro vacuum the surface to collect asample from a 10 x10 cm area of the surface. The sampling procedure follows the American Societyfor Testing Materials (ASTM) method D 5755 - 95. A conductive asbestos air sampling cowl with a0.8 µm pore size mixed cellulose ester and backing filters with the plug from the front cap removedwas fitted with 1.5 - 2 cm long piece of connecting tube with a edge cut at about 450 (see figure 17).

Fig 17: Micro-vacuum sampler


19

Cut plastic tubing

single hole head

conductive cowl

filter

backing filter

to pump

Air was sampled through the assembly at 13 l/min using an air sampling pump and the cut plasticnozzle was dragged slowly across a marked 10 x 10 cm area on the surface. The area was sampledin 4 different directions; up and down, left and right, diagonally from the top left hand corner to thebottom right and diagonally from the top right to the bottom left. Although this was time consuming, itwas done in order to cover the maximum surface area. When dragging the small nozzle end along asurface it is almost impossible to either keep in a straight line all the time or vacuum a line exactlyparallel to the one previously sampled. Small gaps appear between each line and not all the surface is sampled. A higher pump flow rate than the ASTM method, was used to generate a higher inletvelocity (7.66 m.sec-1 ) to the tube and to reduce particle losses in the cowl. The ASTM methoduses a wash procedure to collect particles depositing on the inside walls of the tubing and cowl butfor simplicity, speed and practicality as an on-site method, only the material collected directly ontothe filter was analysed using PCM with MDHS 59 counting rules.

4.1.4. Filter swabs

A common technique employed by U.K. laboratories to measure surface contamination is to placean air sampling filter directly onto the surface and to apply pressure across the filter back to helpattach particles. The filter is then prepared for PCM and counted in the normal way followingMDHS 59.

4.1.5. Adhesive tape sampling

‘Sellotape’ and ‘Scotch Magic Tape’ and other types of readily available adhesive tapes have beencommonly used for sampling surface dusts and the media can be relatively easily prepared for PCMexamination. The adhesive side of the tape can be applied to a surface and pressure applied to helpincrease the ‘pick up’ particles and fibres. This can then be placed or stuck on a glass slide and theconcentration of fibres on the surface of the tape counted using PCM following MDHS 59. Alterna-tively a dispersion liquid can be placed on the glass slide before placing the tape, or the tape can besandwiched between two dispersion liquids a glass cover slip placed on top to improve the image. Ifthe tape is stuck directly on the glass slide, the sample plane of the tape is very close to the opticalplane of the glass slide and the imperfections in the surface of the slide may interfere with the analysis.Figure 18 shows an example of asbestos fibres picked up by adhesive tape during a site clearanceassessment.


20

Fig 18: Fibres collected from a floor surface inside an enclosure with adhesive tape

The method most commonly used at the field sites did not use a RI liquid as a high contrast could beobtained in air. One disadvantage of the tape method is that it tends to ‘pick up’ all sizes of particlesand the sample plane is on the level of the tape surface. When this is made flat the optical sampleplane may undulate, or may not be consistent, requiring the analyst to persistently refocus in order to‘find’ the fibres. This may also occur if the tape is place on a glass slide with an RI liquid. Adhesivetape samples can also be analysed to check fibre type. Larger fibres can be picked from the tape forpolarised light microscopy (PLM) analysis by MDHS 77 or the tape can be prepared and analysedby scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA) to classify thetypes of fibres present (MDHS 87). The latter is an off-site analysis.

4.1.6. Transparent forensic tape

Forensic tapes have an advantage over adhesive tapes in that the adhesive gel layer is much thickerand the tape can mold itself to the surface to give better pick up of particles on rough surfaces.Forensic tapes come in various forms and the backing can be transparent, white or black in colour.The surface of the gel is protected by a removable plastic film that can be replaced after sampling toprotect the surface. To sample, the protective plastic cover is removed and the adhesive layer isplaced onto the surface. An even pressure is then applied across the back of the tape to help molditself to the surface and to increase the pick up of surface particles. The gel has a very clearbackground for microscopic analysis and will produce weak dispersion colours with amosite fibres, ifthe appropriate dispersion liquid is placed under a glass cover slip on the gel surface. However, notall the optical properties are obtained. This is because the plastic backing material attached to the gelacts as a polariser and prevents the observation of some of the optical properties (i.e.first order redcolours and parallel extinction). With care the backing material can be removed to overcome thisdifficulty.


21

The polarization of light by the plasticbacking causes some of the opticalproperties used for PLM identifica-tion to be lost.

Easy to use and store samples. Gives agood PCM mount and background forfibre counting. Can be used for identifi-cation of large fibres. Can be used on awhole range of surfaces with goodpickup.

Forensic tape

Limited pick up on rough surfaces.Focal plane is not always on thesame level. The adhesive ages andthe tape may have striations whichinterfere with the fibre count. There is some interference from theglass slide,

Easy to apply and uses readilyavailable cheap materials.SEM of PLM can be used to identifyasbestos fibres

Adhesive tape

Is not very efficient at picking upparticles, not suitable for rough ordamp surfaces.

Easy to apply, no new equipmentrequired.

Filter swabs

Time consuming. Not very efficient atpicking up fibres and particles.

Equipment is available on site, gives aquantitative result.

Micro vacuumsamples

Based on subjective visual assess-ment and does not discriminatebetween fibres and particles.

Easy to apply, quick, sensitive test ofsurface dust levels.

Torch / beamtest.

Based on subjective visual assess-ment and does not discriminatebetween fibres and particles.

Easy to apply and materials are readilyavailable, and no instrumental analysisrequired. Can be performed usingunskilled labour.

Wipe test. DisadvantageAdvantageTest

Table 4: Summary of Advantages and Disadvantages of Each Test

4.2. HSL clearance air monitoring

Brushing was chosen as the HSL method as it had the potential to resuspend settled dusts, it did notrequire electrical power and represented a typical activity that a worker, cleaner or householderwould be expected to perform in the first stages of cleaning an area that had undergone somerenovation or building work. A brush with polypropylene bristle was chosen to minimise the possibleevolution of vegetable or wood fibres. MDHS 39/4 states that the minimum time for disturbanceshould be “for at least 5 minutes”. In the vigorous comparision the brush test was performed for 5


22

minutes at most sites < 50 m2 and for 5 minutes approximately every 50 m2 at other larger sites for amaximum of 15 minutes. At one site the brushing was carried out for only for 2.5 minutes. Due totime constraints, and the fact that very often workmen were waiting to proceed with other work, theHSL clearance air monitoring was carried out for 30 minutes at most sites.

5. SITE VISITS AND OBSERVATIONS

A total of 20 site visits were made. Fifteen sites had enclosures still intact and clearance assessmentswere carried out, two larger sites had an additional visit to look at different enclosures making a totalof 17 clearance assessments. Due to the logisitics in arriving at the start of the clearance the siteanalysts clearance procedure was monitored at only 11 of the 15 sites, observing a total of 12 clear-ances involving 11 different analysts from 6 different laboratories. The removal sites varied in sizefrom a small boiler room to a large multistory car park. A range of materials were removed, 4 visitsinvolved the removal of ceiling tiles, 3 involved the removal of lagging, 4 involved board removal, and5 involved the removal of sprayed asbestos. The proportion of visits involving each asbestos materialis shown in a pie chart in fig 19 below. Three further visits were made to premises after a removaloperation was completed and clearance given.

Fig 19: Type of Material Removed At Enclosures (17 Total)

Ceiling Tiles6% AIB Ceiling Tiles

18%

Pipe Lagging18%Sprayed

28%

AIB24%

AIB and Lagging6%

5.1. Arrangements

All visits were arranged after consulting and informing the local FOD inspector responsible forasbestos. The sites were chosen through contacts with the analytical laboratories who were eitheremployed to do the clearance assessment or were actual asbestos license holders and were super-vising the site and subcontracting the asbestos removal work. The laboratories contacted the appro-priate persons to inform and agree to HSL sampling personnel be present during the clearanceassessment. All the laboratories approached were accredited for sampling and analysis by the United


23

Kingdom Accreditation Service (UKAS). Obviously, this arrangement will produce a bias, as all theremoval contractors were forewarned that HSL analysts would be visiting the site and may havecarried out additional cleaning. Also, the clearance analysts were also aware that they were beingchecked and would be demonstrating what they considered to be best practice. On severaloccasions and with one laboratory in particular, various hindrances such as providing incorrect infor-mation of the location of the site or continually postponing the visit and then not informing HSL whenthe clearance took place, added to the suspicion that the field study was essentially limited to currentbest practice.

Alternative strategies were considered, e.g. to arrive unannounced at the site, but the logistics andtiming this would involve was not considered to be practical by local FOD inspectors and it was feltthat seeking the co-operation of the analysts and contractors was the best option.

5.2. Personal protective equipment and decontamination procedures

Most analysts wore a half face rubber mask fitted with high efficiency P3 filters (APF of 20). Oneanalyst wore a paper 3M 8810 mask (APF of 10) . All the analysts wore protective paper overallsover their clothes, although only at 3 sites did analysts wear protective paper overshoes. Someanalysts wore safety boots while others wore their own shoes. Only one analyst changed their shoeswhen leaving or entering the enclosure. Frequently, a bucket of water was present in the airlock sothe analysts could wash their shoes. However, this water was not clean and had been used by theremoval contractors for decontamination. It is recommended that analysts use the contractor’shygiene facilities to decontaminate but this did not occur on any of the site visits. Usually, the analystssimply removed their protective equipment once outside the enclosure. It was also found that manyof the hygiene units had already been disconnected before the clearance assessment had beencarried out, presumably because the contractor felt confident that the site would pass. Severalanalysts were also carrying out reassurance sampling in the decontamination units at the same time asthe clearance air monitoring. One analyst mentioned that he only changed his paper suit betweenclearance operations, if the clearance assessment failed.

5.3. Observations inside the enclosures

5.3.1. Dryness of the enclosures

In 5 enclosures (29 %) the area was still very wet (>10% of floor area covered by puddles ofwater), at two others there were areas that looked damp in places and at a further two there werepools of ‘almost’ dry PVA. One of these wet sites was unavoidable as this took place in a basementof a church where a natural spring seeped through the brick walls. PVA solution was sprayed liber-ally at all sites before clearance assessment. The condition of enclosures is summarised in figure 20.


24

Fig 20: Dryness of Enclosures

Dry47%

Wet29%

Damp Areas24%

5.3.2. Size of the enclosures and ventilation

Eleven of the enclosures were between 10 - 150 m3 , the other four sites were all larger than 600 m3.The largest enclosure volume encountered was about 1750 m3. At two sites the area where theceiling tiles were removed was about 10 m above the floor of the enclosure and at another site 6 mabove the floor of the enclosure. The air extraction units were turned off at all sites during the airtesting. Only at one site was the extraction unit left unsealed during the test and at another an air ventinto the area was not sealed. A smoke test showed air being drawn into the enclosure through this airvent when the extraction units were functioning during the visual assessment. The estimated floor areaof each enclosure is summarised in the figure 21.

Fig 21: Estimated Area of Enclosures Examined

< 50 m254%

50 - 200 m27%

200 - 500 m213%

500 - 1000 m213%

> 1000 m213%


25

5.3.3. Robustness of the enclosures

Generally, the enclosures were fairly intact with some notable exceptions. One of these sites was anoperation to remove a board attached to a riser door on the first floor of a sports centre. To achievethis they had decided to wrap and remove the whole door and dispose of it as asbestos waste.However the bottom of the riser on the bottom floor was completely open and not sealed. Anydebris or dust may have fallen down the riser and contaminated the bottom floor. At a different sitethe enclosure had several small holes pierced in the plastic and the dirty end of the 3 stage air locknot only had access into the enclosure, but a single flap also gave access to other parts of the boilerroom not subject to the removal operation. It can only be concluded that this access was requiredfor other workers not involved in the removal operation to enter the boiler room.

5.3.4. Visual cleanliness of the enclosures

In most cases the analysts performed a thorough visual assessment for macro contamination with atorch. The torch was however only shone directly at surfaces and was not used at low incidence tolook for fine dust. Only two sites (11%) failed the clearance because of obvious macro asbestosdebris being present on surfaces (e.g. attached to a pipe and debris in lighting cable conduits). Inmany cases the analyst became part of the cleaning operation and removal workers would bepresent with the analysts with cleaning equipment to follow the analysts instructions. Often the analystthemselves would use the vacuum cleaners to clean up areas of contamination. In 12 out of 15 enclo-sures the floors were visibly dirty, suggesting that no proper cleaning had been attempted and all butone site failed the wipe test. At one site the contractor had not even bothered to remove articlesremaining in the enclosure or attempted to cover them with polythene to protected them fromcontamination.

5.3.5. Use of floor linings

Only at 5 of the sites (33 %) had a protective covering been used to prevent asbestos contaminatingthe original floor. At one of these sites the protective surfaces appeared very clean but had a veryhigh concentration of free fibres. Two of the enclosures were built at height on scaffolding andpolythene was essential to cover the gaps in the scaffold boards. At the other two sites, theworkmen had stated that they had covered the floor with plastic and had taken it up for the clearancetest. However, very high free fibre concentrations were found on the floor (200 - 1000 f/mm2) . Theremoval process they described involved the wet vacuuming of each plastic layer and the floor.Probably water carrying a suspension of asbestos fibres had seeped through holes in the plasticsheeting.

5.4. Clearance air sampling by analysts

All the pumps used by the analysts were set and checked against calibrated rotameters to sample at8 l/min. Each analyst could provide a record of when the calibration for the rotameters they wereusing was last performed and when it was next due. On most occasions (all expect 2) the analystscalibrated their pumps before entering the enclosure. Only one analyst on one occasion corrected theflow rate for temperature and pressure; although this is not critical. Most analysts (75%) used a


26

plastic bag to disturb the air, some filled it with air and banged the walls, others flapped the emptyplastic bag in the air. The methods of disturbance are summarised in fig 22 overleaf. Generally, verylittle of the surface area of the enclosure was disturbed and the period of disturbance in all caseslasted for 5 minutes regardless of the size of enclosure. This would make the test less sensitive forlarge areas. Only one analyst disturbed any significant area of the floor; the largest flat surface area inany room. Most disturbances were performed with the air pumps sampling. On a very few occasionswas it noticed that the flow rate was checked at the finish inside the enclosure. However, the analystwould usually take the pumps outside the enclosure and it was not observed whether the pumpswere set running and the flow rate rechecked.

Fig 22: Disturbance Methods Used by Analysts

Wiping With Cloth18%

Hitting Surfaces with Inflated Plastic Bag

37%

Clip board13%

Brushing with clip board

6%

Plastic bag with weight13%

Shaking Plastic Bag13%

Only at two sites (11%) did the analyst fail the clearance, due to the initial air test result exceeding0.01 f/ml.

6. FIELD EXPERIENCE WITH THE SURFACE SAMPLING METHODS

6.1. Wipe samples

Only one enclosure passed the wipe sampling test. Interestingly this removal operation was managedby a company whose background originated from the cleaning industry rather than the demolition orbuilding trades. The amount of fine dust and dirt remaining suggests that the methods of cleaningemployed by removal operators are either ineffective or that they have learnt that this surfacecontamination is unlikely to be the cause of a clearance failure by the current practices and standardsused by the analysts.

Type H vacuum cleaners were found at all sites and were used during the clean up, however theability of vacuum cleaners to remove finer dust which is bound more tightly to the surfaces isquestionable. This was investigated by taking floor samples taken before and after vacuuming andsimilar results for the number of free f/mm2 before and after vacuuming were found. Vacuuming wasalso used in conjunction with mopping and at some sites vacuuming was taking place after mopping,


27

which would make the particles even more difficult to remove. Again traditional mopping of a floorsurface does not produce a very efficient removal of contaminants and a more careful wiping withdisposable materials ensures that the contaminants are not reapplied to the surfaces. The wipemethod is not suitable for use on rough surfaces such as concrete floors and tarmac.

6.2. Low angle torch test

This test was found to be very effective at finding surfaces contaminated with dust particles.However, it is not appropriate for use on rough surfaces such as concrete or wooden planks. Alsothe question of whether a surface is dirty is subjective and there could be differences of opinionbetween analysts. Other analysts who were asked to perform the technique in an enclosure oftenwould not completely understand the importance of the low angle of incidence to detect the fine dustand after a while would lapse into their normal procedure of pointing the torch directly at the surfaceof interest. Most analysts when questioned, tended to consider a surface as dirty only if they sawevidence of larger pieces of debris rather than a fine deposit of dust.

6.3. Vacuum, filter swab and tapes samples

6.3.1. Results

The differences between the surface sampling methods are shown in figure 15. The vacuum samplesare not shown as the figures for the number of f/mm of surface area are almost 100 to 2000 timeslower than the direct sampling methods. The vacuum technique was found to be less efficient atsampling than the adhesive or forensic tape.

Fig 23: Comparision of Effectiveness of Sampling Medium

0

200

400

600

800

1000

J J J J J J J J J J K K K K L L L L L M M M N N N N N N N N2

N2

N2

N2

O O O O

Site

Fibres/mm2 on surface

Sello tape Filter Swabs Forensic Tape

In 92 % of comparative results (34 in 37 cases) the filter swab samples obtained lower results thanthe adhesive tape samples. The three cases where the results were higher were from: the plasticfloor of a 3 stage air lock at a site where the general contamination level was low for all surfacesamples; on a metal girder, where the sellotape picked up a lot of rust particles which obscured thefibres, and on a cardboard floor, where the ‘Sellotape’ samples were taken from the smooth surfaceof the tape that held the boards together; to avoid ‘picking up’ the cellulose from the cardboard. In


28

73 % of cases (16 in 22) the counts were higher for the forensic tape samples than for thosecollected on ‘Sellotape’. However, as about half of the comparable results had fibre counts whichcould not be considered statistically significant, the sites which gave the largest differences wereexamined. Overall, comparable results with the forensic tape were mostly obtained on smoothsurfaces. The forensic tape obtained much higher results on wood or varnished wood at site L, at siteM all the results were low, at site N significantly higher results were obtained for samples from thecard board floor and site O obtained much higher results from the tarmac surface. Sellotape can notefficiently sample the surface on cardboard and the samples had to be taken on the smoother tapesurface sealing the boards together.

6.3.2. Discussion

The field experience showed that the micro-vacuum technique had lower collection efficiency thanadhesive tape sampling. This was due in part to the wall losses not being included in the analysis, theair sampling filters were examined directly. When the magnitude of the wall losses was estimated itwas found that 15 - 25 % of fibres remain on the cassette and piping under the conditions used. Asimilar finding about the poor efficiency of vacuum samples was obtained in other work (appendix5). Sellotape appears to be an efficient sampling medium but its effectiveness is limited by somesurface types such as cardboard. Forensic tape was found to be the most versatile and efficientsampling medium over a range of surface types.

7. RESULTS OF THE CLEARANCE AIR MONITORING

7.1. Site analyst results

The fibre counts from the site analysts were not obtained, but as only two sites failed the clearanceair monitoring results (sites L and N) but both passed after recleaning and a single retest This meansthat 13 of the 15 sites (87 %) passed on the first clearance air monitoring test. As two sites hadmultiple enclosures, a total of 15 of the 17 enclosures tested (88%) passed on the first clearance airmonitoring test. All passed after the second clearance air monitoring test. As site L was a smallersite, in terms of samples taken, it is estimated that over 95% of the sample would have had concen-trations below the clearance indicator (<0.01 f/ml).

7.2. HSL concurrent results

The results from HSL samples taken concurrently and alongside the site analysts’ own clearance airsampling, where the site analyst carried out the disturbance, are shown in table 5.

<0.016604.52042<0.01720102001B

ResultFibres/ml

VolumeLitres

FibresFieldsSampleSite

Table 5: Results from samples taken during analysts disturbance


29

Area not passed by the analyst 1st time and only 1 sample run duringsecond clearance.

0.014805220960.016003020650.015402320040.0148031.522130.0260039.520120.01480322521O

<0.0142962102<0.0166024.52001M<0.01467.518.520110.07*60011714420.06*576101.51341L<0.0142922.52002<0.01660292001K0.0260042.52025

<0.016722021140.03480522013

pump failed1006320020.0251243.52311J

<0.015287.52025<0.0148027.52114<0.01480222013<0.01660352002<0.0167038.52311I0.01466039.520420.016600452271G<0.0166014.52092<0.01660142001F0.01160026.520130.0146604021020.012660312011E<0.0160011.52002<0.0166092001D

The results from the concurrent samples were analysed off site at HSL. Due to the difficulty in arriv-ing before the site analyst began clearance only 11 sites were monitored concurrently, as a retest wascarried out at site L a total of 12 enclosures were monitored. Only 7 of the 11 sites (64 %) and 8 ofthe 12 enclosures (67 %) monitored concurrently, passed the clearance air monitoring according tothe HSL fibre counting. Of the 33 samples taken and analysed by HSL only about half (17/33 or52%) were found to be below the 0.01 f/ml clearance indicator. The four sites which failed consis-tently gave fibre concentrations >0.01 f/ml (10 of the 11 samples) suggesting that these were signifi-cantly above the clearance indicator. The one site failed by the site analyst also gave the highest fibreconcentrations in the HSL analysis (0.06 - 0.07 f/ml). There was a consistent bias that the field


30

analysts counted lower than HSL. This bias was particularly significant in deciding whether the sitehad passed or failed, and the percentage of samples recording fibre counts of <0.01 f/ml fell from>95% to 52%.

7.3. HSL clearance air monitoring results

As far as possible as soon as the concurrent sampling had finished a further more vigorous clearanceair monitoring test was carried out by HSL staff using a brush or broom to sweep surfaces for fiveminutes. The same type and length of disturbance was used at each site and the samples collected aslong as possible before the contractor started to take down the enclosure. At several sites thislimited the sampling time to around 30 minutes and additional fields of view were counted tocompensate for the lower sampling volumes, so a similar air volume and limit of quantification couldbe achieved for each sample.

The HSL results from clearance air monitoring where a brush or broom was used to disturb thesurfaces for five minutes, are given in table 6.

√0.0170.0843001001913√0.020.083240822002√0.0150.06631586.52001Jx0.010.00948017.52005x0.0104800.52104x0.0080.006600142003x0.0450.0171007.52162x0.0070.0046009.52161I

Air samples not required:- Heavy contaminationH√0.0130.03618756.54012√0.0140.039170554031G√0.0070.00933023.54012√0.0060.01438543.54031F√0.0160.02930035.52003√0.0150.058330782002√0.0130.06633097.52201_E√0.0090.0348463.52132√0.010.03447364.52001D

2Too heavily loaded with particles

1Cx (site very wet)0.0080.00530011.54021B

√0.0080.017600422051A

Results AboveDetection Limit

Detection LimitFibres/ml

ResultFibres/ml

VolumeLitres

FibresFieldsSampleSite

Table 6: Results from vigorous comparison test


31

√0.0340.21270124.51066√0.0330.182701071105√0.0350.22401101144√0.0360.212401131113√0.0450.23270101.5792√0.0410.22240106981O 2nd√0.0280.06168392068√0.020.0624056.52027√0.0110.0230043.52896√0.0160.093001072005√0.020.08240802124√0.0190.07240712163√0.020.03216272192√0.020.06240572001O 1stx0.010.00924018.54006√0.010.01333036.54005x0.010.00130024004x0.010.0124019.54003√0.010.01324022.54022√0.010.013240264181N 2nd√0.0180.053270582006√0.0190.097240101.52165√0.020.07724074.52004√0.0330.18270106.51093√0.0210.11240102.51892√0.040.232401111011N 1st√0.0150.0230027.52212√0.0140.018330252111M√0.0280.16510116.5692√0.0350.19480103571L√0.020.036240362032MDHS 59

√0.0160.043300532001MDHS 59

√0.010.02424048.54022√0.0080.0130025.54061K√0.0150.054315712015√0.0180.065270722004

HSL carried out clearance air monitoring and disturbance at 14 of the 15 sites, one site was visuallycontaminated so was not sampled. One further site produced such high levels of particles the filterswere not countable. It was assumed that if a site is this dirty it has failed the clearance air monitoring.

Given the above, only one of the sites passed the clearance assessment based on the HSL monitor-ing where all of the results from the site were <0.01 f/ml. The site in question was very wet and hadan underground spring which covered the floor in water, and only a single sample was taken. One


32

further site had an average air concentration based on 5 samples of 0.0098 f/ml but as four of thefive samples were > 0.01 f/ml, this would according to MDHS 39/4 be considered to be a failure.Therefore only one of the 15 sites (7%) passed when the clearance assessment was carried out byHSL.

Of the 53 individual air samples 43 (80%) were > 0.01 f/ml. The average concentration inside theenclosures during clearance sampling was 0.068 f/ml with a range of 0.23 to 0.0002 f/ml. Theaverage air volume sampled was 306 L with a maximum of 600L and a minimum of 100L. These airvolumes were lower than the recommended minimum of 480L due to the logistic problem of theContractor wanting to take down the enclosure as soon as the site analyst cleared the site. In themost extreme case the site analyst cleared the site and the removal contractor wanted to take downthe enclosure after only 17 minutes of re-sampling by HSL. As explained this problem wasovercome by counting additional numbers of fields of view, unless the initial fibre count was about 50fibres and the recount would give very little increase in precision of the analysis and the site wouldcertainly be above the clearance indicator.

The average number of fibres counted for each sample was 60 fibres, the lowest count was 0.5fibres counted. Counting was discontinued after about 100 fibres. This means that there is reasonableconfidence in the precision of the results and that the clearance indicator of 0.01 f/ml based on acount of >20 fibres in 200 fields of view was being exceeded. Where the results were close to theclearance indicator limit, for 200 fields of view, a recount was done on a further 200 fields to ensurethat the results were comparable with the recommended volume of air analysed. As blank filtercounts were in the range of 0.6 - 1.6 f/mm2 the additional filter area counted will not have a signifi-cant affect on the average fibre count.


33

Plastic bag with weightNoWet 800 - 1080Not knownNot KnownSprayedO (2)Plastic bag with weightNoNo * (No)P (P)Wet 800 - 1080Not knownNot KnownSprayedO (1)

Inflated plastic bagsomeYes(some)F (P)PVA pools324 m2Not knownAmosite andchrysotile

SprayedN (2)

Inflated plastic bagsomeYes(some)F (F)Dry700 m2Not known > 25 m2

Amosite andchrysotile

SprayedN (1)Inflated plastic bagsomeYes(some)P (P)PVA pools22 m221 m2Not knownAIBMWiping with cloth NoYes (No)P (F)Wet9 m20.8 m2AmositeSprayed L

Brushing with clipboardNoNo (No)F (P)Dry4 m21 m2AmositeAIB KInflated plastic bagsomeParts (No)P (P)Dry78.5 m278 m2AmositeAIB Ceiling tilesJ

Inflated plastic bagsomeNo (No)P (P)PVA pools360 m2Not knownChrysotileand amosite

Chrysotilelagging and AIB

I

Waving board pipeNo testNo (No)F (ND)Dry2 m longpipe

Amosite andchrysotile

Pipe laggingH

Wiping with clothNoNo (some)P (P)Dry16 m23m longpipe

Not knownPipe laggingGShaking plastic bagNoNo (some)P (P)Dry15 m24 m2AmositeAIBFShaking plastic bagNoNo (No)P (P)Dry600 m2600 m2Not knownCeiling tilesE

Clip boardNoYes (No)P (P)Wet PVA6 m26 m2AmositeAIBD

Clip boardNoNo (No)P (P)PVA Pools10.35 m210.35 m2Not knownAIB Ceilingboards

CInflated Plastic bagNoNo (No)P (P)Wet50 m2Not knownNot KnownLaggingBWiping with clothNoNo (No)P (P)Dry8 m28 m2AmositeAIB Ceiling tilesA

Type of DisturbanceFloordisturbed

Floorcovered &

visuallyclean

Visual &(air test)Pass/Fail

Wet/DryEstimatedArea of

Enclosure

EstimatedArea of

AsbestosRemoved

Type ofAsbestos

Type of ACMSiteTable 6: Summary of Sites Visited


34


35

7.4. Reasons for differences between HSL and field analysts

There could be several reasons for the much higher failure rate when HSL carried out the distur-bance sampling:

� HSL analysts are biased towards over counting or field analysts are biased to undercounting;

� Differences in the disturbance methods;

� Shorter sampling periods;

� Blank counts;

� Psychological factors.

HSL samples were counted by three different analysts and introduced randomly into the system sothere was no reason to suspect any systematic difference due to the laboratory. HSL, as well as theother laboratories participate in the RICE inter laboratory quality control (QC) scheme, all the count-ers performance are also monitored by regular intra-laboratory QC samples. As a laboratorycompared with the RICE average HSL has a negative bias and tends to undercount compared withthe average of all the laboratories.

The disturbance method used (sweeping for 5 minutes) is one that is recommend for use by HSEguidance. However, in laboratory comparison and comparative field tests this method tends to bemore vigorous and produces higher dust levels. However, it can be argued it is a far more represen-tative and likely activity than the disturbance methods used by the field analysts.

The time of sampling from the work in this report is important in that the concentration does start todecline more noticeably after 30 minutes and the average concentration will be reduced Again wewould argue that it is better that the sampling period is shorter or the disturbance should be morefrequent, to prevent significant dilution of the clearance indicator.

Even so when concurrent sampling was carried out where the field analyst used their own method ofdisturbance and the same sampling periods and rates were used with side-by-side sampling, HSEstill reported a significantly greater number of samples and sites above the clearance indicator. Blanksamples are routinely analysed and for this survey were typically around 1 f/mm2 and the additionalfields counted (200 graticules = 1.5 mm2) would have only a small effect on the fibre count and isunlikely to make a significant difference to the number of samples and sites failing (considering anaverage of 60 fibres were counted on the HSL samples and the indicator is based on a count of 20fibres). This leaves and suggests that there is a factor involved with the counting of fibres on site,where there is clearly time, financial, business and peer pressure directed towards achieving a siteclearance as quickly as possible. It should also be remembered that this survey was done with thehelp and co-operation of the analysts and contractors in full knowledge that HSL would be visitingand sampling the site, which would tend to produce a bias towards best practice.


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7.5. Relationship between Surface Sampling Technique and AirConcentration

Figure 24 showed that a limited correlation (C.C. = 0.57, slope = 0.048) between average fibreconcentration on the floor vacuum samples and average air concentration from the broom distur-bance test were obtained over the 11 sampled sites.

Fig 24: A Comparision Between Surface Concentration And Air Concentration for Samples Taken by Vacuum Method

0.01

0.06

0.11

0.16

0.21

0 0.5 1 1.5 2 2.5 3Surface fibres/mm2

Air

Con

cent

ratio

n f/m

l

The highest value determine by this technique as the surface concentration of fibres that passed aclearance test was 0.8 f/mm2 this is equivalent to a concentration of fibres on the filter of 21 f/mm2.This suggests that if this technique is used and a concentration of greater than 21 f /mm2 is collectedon the filter it is unlikely to pass a vigorous disturbance test.

Fig 25 gives the same comparison for the ‘Sellotape’ samples which shows no correlation suggestingthat the collection efficiency for this sampling method, although more efficient than the vacuumsamples, is very dependent on the type of floor surface sampled. The adhesive tape samples do notwork well on rough or wet surfaces.

Fig 25: A comparision between air concentration and surface concentration for samples taken with the sello tape method

0

0.05

0.1

0.15

0.2

0 20 40 60 80 100 120 140 160 180

Concentration On the Floor (F/mm2)

Air

Con

cent

ratio

n of

Bru

sh

Tes

t f/m

l


37

By contrast the forensic tape samples (figure 26) in a series of comparisons appear to work well on

most surfaces and the data suggests that there is a good correlation (0.76 and slope = 0.0004)between average floor concentration and median air concentration. The highest surface concentra-tion value that would have passed the vigorous clearance assessment gave a value of 122 f/mm2.This would suggest that values above this are unlikely to pass a vigorous disturbance. The high resultat 0.1 is based on a limited number of samples from a very large enclosure and small specks ofdebris on the floor may have ‘broken up’ during brushing.

Despite the lower sampling efficiency of the vacuum samples, it was encouraging that a correlationwas present over the 11 sites. Depending on where the asbestos was and how it was removed itwould be expected that their would be large variations in fibre density across the floor surface. Thesesurface variations could potentially be far larger than the relatively small differences in airborneconcentrations measured. It would appear that the larger the area that is sampled (100 cm2 forvacuuming) and integrated, the more chance that local variations will be averaged.

Variability in sampling efficiency will add a further confounding factor and it was thought that thisvariability was the main reason for the sellotape having no real correlation. Certainly a number of thesites were wet and would be a challenge to any surface sampling technique. However, single tapesampling has no integration so has much more variability then vacuuming samples. Multiple impres-sions would help to overcome some of the variation but the relatively low tolerance to particle sizemeans that the efficiency of pick up would drop rapidly once a few large particles were attached.This is the main advantage of the forensic tape with a much thicker collection media it can potentiallygive more uniform and repeat sampling. Also the sampling efficiency should give a better averagethan tape lift samples. However, sampling efficiency is of secondary importance compared to reproducibility.


38

Fig 26: A comparision between air concentration and surface concentration for samples taken using forensic tape

0

0.1

0.2

0.3

0 100 200 300 400 500 600

Counts On Surface (f/mm2)

Con

cent

ratio

n In

Air

(f/m

l)

8. PERSONAL EXPOSURE WHEN REMOVING ENCLOSURES

A limited study was carried out to measure the airborne levels released when the enclosure is takendown. When this operation was observed, no or minimal respiratory protection, (e.g.such as 3m8810 paper masks with a APF of 10), was worn. Those with masks were also observed takingbreaks inside the enclosure, removing their paper masks and smoking. If the disturbance and physi-cal assessment performed by the analyst during clearance was ineffective, or trapped pockets offibres are present in the folds of the enclosure, the workers could inhale their highest exposuresduring the whole removal process, as they are no longer protected by high efficiency filters and fullface powered respirators. Personal and background samples were taken during removal of thesecond enclosures at sites N and O and during the removal of the small enclosure at site P. Theresults are listed below in tables 11 and 12.

At site N (2nd enclosure) a number of workers were involved in the de-sheeting process. Thisoperation lasted 3 hours and involved removal of the plastic and floor boards on top of the woodenplanks. These were thrown from the platform to the concrete floor below. The de-sheeting operationat site O lasted about 2 hours. The removal operation was broken up with intermittent smokingsessions. Site P was a relatively small enclosure and the de-sheeting work only lasted 50 minutes.Three workers were involved in the de-sheeting process. One worker sprayed the inside liberallywith PVA solution, the other two took the plastic sheeting down and stuffed it into plastic sacks tobe disposed of as asbestos contaminated waste.

4hour TWA =control limit assuming no further airborne exposure<0.01< 0.05Mr Roberts<0.02< 0.071Mr MitchellP

0.070.13Mr Alan0.080.16Mr Corning0.090.172Mr GeeO

0.090.163Mr GreensN

4 hour-TWA(f/ml)

Measured Conc.(f/ml)

Approximate timefor removal

(hours)

Worker Site Identifier

Table 11: Summary of personal sampling results during the removal of the enclosure

< 0.0310De-sheetingUnder scaffold N

Peak Exposure(fibres/ml)

Sampling time(minutes)

Operationsampled

LocationSiteIdentifier

Table 12: Summary of static sampling results during the removal of the enclosure


39

0.02Centre of enclosure0.02Centre of enclosureO0.0260Floor removalUnder enclosure

0.0270De-sheeting +floor removal

Under enclosure

The results show that personal exposures close to the 4 hour control limit were generated during theremoval of enclosures. The static samples were much lower, about one tenth of the control limit.De-sheeting of large enclosures took 2 - 3 hours. At smaller enclosures much lower levels occur andthe sampling times are limited. Background levels of fibres at the two larger sites were consistentlyabove the clearance indicator of 0.01 fibres/ml.

9. VISITS TO PREMISES AFTER CLEARANCE

Post-clearance visits were made to three sites (L, N and P), the results of these visits are describedappendix 6. All three sites had visible asbestos-containing debris left after the site had been clearedand the enclosure removed. Similarly all sites were visibly dirty or very dirty based on a visualinspection. One site had a room full of the removed non-asbestos paneling which had presumablybeen removed to allow access to the ACM and was going to be replaced. This was also visiblydirty. Adhesive tape samples were taken and all sites had countable levels of fine fibres as well as themacroscopic debris. The highest levels for the Sellotape sampling were at site L which gave levels of48 and contamination 76 f/mm2, site N was the next highest with an average level of about 15 f/mm2

and site P was the lowest with levels around 2 f/mm2.

Due to the lack of any containment, it was felt appropriate to carry out a disturbance type air test atonly one of the sites. Site L , had failed the initial site analysts clearance and passed on the secondclearance (where parallel sampling was not carried out or the disturbance observed but a sampletaken soon after by HSL suggested low airborne levels had been raised (<0.01)). Both of the HSLclearance tests, carried out inside the enclosure gave concentrations significantly above the clearanceindicator as did all three samples taken in a post clearance test. The highest value was 0.08 f/ml.Therefore, both from the surface sampling results and airborne results there was significant contami-nation left at the site both inside the enclosure and after it had been removed.

At site N ‘macro’ containing amosite and chrysotile were found in significant quantities under the sitewhere the enclosure had been suggesting that either the site had not been cleaned generally beforethe enclosures were established or that the integrity of the enclosure had been compromised at somepoint and released the asbestos. At site P, while dirty, it seemed that the floor cover had containedmost of the asbestos and the asbestos may have been present on the floor before it was covered andthe pre-cleaning, if done, had not been effective.

What is clear from the three sites, is that there was no effective pre-cleaning of the sites beforeestablishing the enclosure, or any attempt to post-clean, once the enclosure was removed. There wasalso an assumption that no asbestos penetrated through the floor of the enclosure.


40

A separate post-clearance survey (Cottrel, 2000) for macro contamination was carried outindependently at a further five sites by an HSL analyst (sometimes significantly after the removal hadfinished) and found two of the five sites still had ‘macro’ contamination present. Tape samplingtechniques were not used at these sites.

10. CONCLUSIONS

10.1. Experimental observations on: Surface tests

w Wipe tests based on the coloration by surface dust were found to be a simple way toestimate whether surface dust levels are likely to be a problem.

w The likely lower level of detection for aluminium oxide and amosite was measured inlaboratory trials on different wipe media. The Whatman 540 filters and Mediwipes werefound to give a visible contamination line after a 10 cm wipe at aluminium oxide particleconcentrations of about 200 p/mm2 and at amosite concentrations of 60 f/mm2.

w The wipe test appeared too sensitive for the current levels of cleaning in UK enclosures as94 % of enclosures failed the wipe test. However, a similar percentage failed HSL’sclearance air monitoring.

w Although it was not envisaged that the project examine methods of cleaning, observationsof working practices employed in enclosures suggest that the most common methodsemployed; vacuuming and mopping are not very effective.

w The HSL operator found the HSL low angle of incidence torch test very useful to detectsurface dust but could only be used on smooth surfaces. However, different operators arenot consistent with their approach or judgments.

w Adhesive tape was found to be a simple method to sample surface dust and phase contrastmicroscopy could be used to quantify the amount of asbestos fibres on the surfaces.Adhesive tapes can also be treated to allow further analysis by SEM or PLM to identifythe fibres present. It does not, however, work well on rough or damp surfaces.

w Forensic tape produces a clearer mount than adhesive tape for PCM analysis. However,it is limited, if further identification of fibres is required.

� Forensic tape was found to be the most versatile and efficient sampling medium over arange of surface types. Adhesive tapes were efficient for sampling smooth dry surfaces buthad problems with rough or damp surfaces.

� Micro-vacuuming in the simplified form used, was found to be less efficient than tapesampling but gave a more integrated sample, as larger areas or multiple areas could besampled.


41

� A concentration of fibres on a surface of 100 f/mm2, determined using forensic tape,produced a concentration in air of about 0.01 fibres/ml, when an area of about 50 m2 wasbrushed with a hand brush for 5 minutes. This means that the visual wipe test which candetect down to 60 f/mm2 of amosite will have the potential sensitivity to detect surface dustlevels which may fail the clearance air monitoring.

w The surface tests can only provide an indicator of the likely outcome as chrysotile asbestoswill not discolour a white wipe media while other dust particles will. It should also be notedthat the efficiency of surface sampling is surface and sampling media dependent and thearea sampled may not be representative of other areas.

10.2. Experimental observations on: Disturbance / resuspension of surfacedusts and asbestos fibres

w A survey identified that the most common method of disturbing dust in the enclosures wasto shake a plastic bag in the air or to hit a plastic bag full of air against walls. Thesemethods were shown in laboratory tests to be very ineffective methods of dust disturbance(less than one tenth compared to brushing).

w Leaf blowers were found in experimental comparisons to be the most efficient techniquefor resuspending and mixing settled dust, some 4-5 times more efficient than brushing. Themixing action had an important influence on air measurements as the fibres lofted by theleaf blower took longer to settle out and accounted for most of the difference betweenbrushing and leaf blowing.

w The effectiveness of a leaf blower, will be dependent on how close the outlet nozzle is tothe surface. It also requires an electrical supply inside the enclosure. Its efficiency maymean that surface dust levels which may not be detected by a simple visual wipe test mayfail the clearance air monitoring. Also at some of the enclosures sampled, the airbornelevels produced would be likely to exceed the control limit and may put clearanceassessors and removal workers at risk.

w Brushing is another effective method of resuspending surface dust but does not mix anddisperse the particles as efficiently as the leaf blower and that a significant proportion offibres have settle out after about 30 minutes.

w Experiments with ground Amosite asbestos and resuspension of the fibres with a leafblower indicate that 40 % of asbestos fibres settle in the first 60 minutes. With handbrushing there was a sharper decline in the number of airborne amosite fibres which hadhalved after about 10 minutes and over 90% of the airborne fibres had settled out withinthe first 30 minutes after disturbance. This suggests that the sampling period should beshorter (30 minutes or less) and /or fans are used to further mix the dust into the air.


42

10.3. Field Observations: Visual Assessment by site analysts

w In most cases the analyst was involved in a remedial cleaning process rather than aseparate visual clearance assessment.

w The role of the analyst in the clearance process is ambiguous and they need a recognisedindependent role without any financial relationship with the removal contractor.

w No sites had their clearance assessments delayed because they were still wet.

w Analysts would perform the visual assessment using a torch but were mainly looking forlarge debris ‘visible’ contamination, rather than the film of dust which coated mostenclosures.

w Two of the 17 enclosures observed failed the site analyst’s visual assessment because ofmacro contamination with asbestos. One site had several failures before it was finallypassed.

10.4. Field Observations: Visual Assessment by HSL analysts

w Two thirds of enclosures did not use any covers on the floors and which meant they wereleft unprotected from falling contamination.

w Some of the uncovered floors consisted of concrete or tarmac whose rough surface wouldmake it almost impossible to clean up fine asbestos dust.

w All but one of the floors of the enclosures were left visibly dirty with dust (as determinedusing a simple wipe test and low angle torch test) but nearly all had passed the visualassessment by the site analyst.

w Many sites had sprayed the enclosure with PVA before the visual assessment, making therecognition of fine debris and dust more difficult.

w Glass fibre insulation was left in place inside several enclosures. Potentially this glass fibrewas contaminated, as it was left uncovered and it should be recommended that it isremoved at the same time as the asbestos. It also makes the analysts position more difficultas they do not disturb this material because it will produce fibres if disturbed during the airtest.

w Over half of the enclosures were either wet (29%) or damp (24%). Often this was due tothe liberal spraying of PVA solution before the clearance assessment and insufficient timebeing given for the enclosure to dry.


43

10.5. Field Observations: Clearance air monitoring by site analysts.

w All analysts would disturbed the enclosure area for 5 minutes, regardless of the size of theenclosure. This made the method less sensitive for larger enclosures.

w At some sites the enclosures consisted of several rooms. Again this made the method lesseffective as the air movement will be restricted and the disturbance time in each roomreduced.

w Two of the 16 enclosures failed clearance air monitoring on the first attempt, both of thesepassed on the second attempt.

w Site analysts used a removal sack as the disturbance method in 10 of the 16 (63%)enclosures where clearance air monitoring was observed.

w At 11 of the 15 sites no attempt was made to disturb the floor of the enclosure in spite ofthe fact that this is the obvious place for fine dust to collect. At the four sites where thefloor was disturbed at all, this was done only with an inflated plastic bag where the contactwas pretty minimal and only at two sites was any real attempt made to disturb.

10.6. Field Observations: Concurrent clearance air monitoring by HSLanalysts.

� The results from the concurrent samples were analysed off site at HSL. Only 7 of the 11sites (64 %) and 8 of the 12 enclosures (67 %) monitored concurrently, passed the clear-ance air monitoring according to the HSL fibre counting. Of the 33 samples taken andanalysed by HSL only about half (17/33 or 52%) were found to be below the 0.01 f/mlclearance indicator.

� The one site failed by the site analyst also gave the highest fibre concentrations in the HSLanalysis (0.06 - 0.07 f/ml). There was a consistent bias that the field analysts countedlower than HSL. This bias was particularly significant in deciding whether the site hadpassed or failed, and the percentage of samples recording fibre counts of <0.01 f/ml fellfrom >95% to 52%.

10.7. Field Observations: Clearance air monitoring by HSL analysts.

� HSL carried out clearance air monitoring and disturbance at 14 of the 15 sites. One sitewas visually contaminated so was not sampled and one site produced such high levels ofparticles the filters were uncountable.


44

� Only one of the sites passed the clearance assessment based on the HSL disturbance andclearance air monitoring. The site in question was very wet and had an underground springwhich covered the floor in water

� Of the 53 individual air samples analysed 43 (80%) were > 0.01 f/ml. The averageconcentration inside the enclosures during clearance sampling was 0.068 f/ml with a rangeof 0.23 to 0.0002 f/ml. The average air volume sampled was 306 L with a maximum of600L and a minimum of 100L. These air volumes were lower than the recommendedminimum of 480L due to the logistical problem of the Contractor wanting to take down theenclosure as soon as the site analyst cleared the site.

10.8. Field Observations: removal of enclosures / post clearance

w Workers are often provided with paper masks 8810 type FFP2S with a protection factorof 10. However, many do not wear them when desheeting and some workers will break tosmoke a cigarette whilst in the old enclosure area.

w TWA personal exposures of about 0.1 fibres/ml were obtained from workers desheetinglarge enclosures. This work activity is probably where workers are exposed to theirhighest levels of fibres since whilst removing the asbestos they would have been protectedwith powered respirators with high efficiency filters.

�Post clearance visits were made to three sites. All three sites had visible asbestos-containing debris left after the site had been cleared and the enclosure removed. Similarly allsites were visibly dirty or very dirty based on a visual inspection. One site had a room full ofthe removed non-asbestos paneling.

�Post clearance air monitoring was carried out on one site and gave values of up to 0.08f/ml with brushing.

�Another HSL/HSE survey conducted at the same time as this report found visible asbestosdebris at 50 % of sites visited (3 in 6).

w This suggests that no effective pre-cleaning takes place before the enclosure is constructedand also that no post-cleaning takes place after the enclosure is removed.

11. RECOMMENDATIONS

w Visual assessment should involve a simple standard wipe test to detect theconcentration of fine settled dust.


45

w A standard method for tape sampling to measure the concentration of fibres removedfrom surfaces should be developed for field use by analysts.

w Guidance on how to use low angle light beams to detect fine dust should be given byHSE.

w The visual assessment should assess whether the enclosure was dry. This should be acontractual requirement for the asbestos remover.

w Clear guidance should be given that clearance air monitoring should only be carried outwhen the enclosure is dry.

w The clearance certificate should state that the enclosure was dry at the time of the test.

w A standard disturbance should be specified based on brushing/sweeping.

w The time of disturbance should be adjusted to the size of the enclosure.

w Five minutes should be used as a minimum disturbance time for enclosures less than100 m2 , a further 5 minutes or part thereof should be added for each additional 100m2 up to a maximum of 15 minutes.

� The floor of the enclosure and other flat horizontal surfaces should be disturbed forabout 4 of every 5 minutes (80%).

� All floors and surfaces should be pre-cleaned before the enclosure is established andthen covered to protect them from further contamination. This covering could then beremoved and the air test performed on the remaining surfaces which, in theory, shouldnot be contaminated. Most sites would probably pass the air test if this simple measurewas implemented to prevent the spread of asbestos.

� The site analyst should be more independent from the asbestos contractor and shouldbe employed by client.

� Current guidelines on the use of PVA is not being followed and are consideredimpracticable. A change in guidance is necessary. This is also important in obtaining dryenclosures.

� Use of critical barriers and a double skin of polythene should be considered. This willallow the contaminated polythene to be locked down and removed before anyclearance test takes place.

� Guidance on enclosure removal should stress the risk of exposure to residualcontamination.

� Hygiene units should be functional until the clearance certificate has been issued.


46

�Materials which are likely to be contaminated with asbestos and cannot be coveredshould be removed.

� A post-clearance assessment should be carried out after the enclosure has beenremoved but with the critical barriers still in place.


47

12. REFERENCES FOR THE REPORT AND APPENDICES

ASTM E1368-96 Standard practice for visual inspection of asbestos abatement projects. AmericanSociety for Testing Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428.

ASTM D5755-95 Standard test method for micro vacuuming sampling and indirect analysis of dustby transmission electron microscopy for asbestos structure number concentrations. Volume11.03, 564 - 575, ASTM 1996 yearbook. American Society for Testing Materials, 100Barr Harbor Drive, West Conshohocken, PA 19428.

ASTM D5756-95 Standard test method for micro vacuuming sampling and indirect analysis of dustby transmission electron microscopy for asbestos mass concentrations. Volume 11.03, 576- 587 ASTM 1996 yearbook. American Society for Testing Materials, 100 Barr HarborDrive, West Conshohocken, PA 19428.

Bailey, S; Conchie, A., Hiett, D.M. and Thomas, C. (1988), Personal exposure to asbestos dustduring clearance certification. Annals of Occupational Hygiene. 1988, vol. 32, no.3,423-426.

Booker, D.C.R. and Purnell, C.J. (1990). An investigation into the effectiveness of asbestosmanagement and removal programmes in building. London School of Tropical Hygiene andmedicine.

Burdett, G.J. (1988). Evaluation of aggressive sampling methods, IR/l/DI/88/04, Health and SafetyLaboratory, Broad Lane, UK. S3 7HQ.

Carter, R.F. (1970). The measurement of asbestos dust levels in a workshop environment. AWREreport no. 028/70. Atomic Weapons Research Establishment. Aldermaston, U.K.

CAWR (1998) Control of Asbestos at Work Regulations 1987 SI 1987/2115 (ISBN 0 11 0781155), Control of Asbestos at Work (Amendment) Regulations 1992 SI 1992/3068 (ISBN 011 025738 3) and Control of Asbestos at Work (Amendment) Regulations 1998 SI 1998/ 3235.

Chavalitnitikul. C., Levin. L., (1984). A Laboratory Evaluation of Wipe Testing Based on LeadOxide Surface Contamination. Am. J. of Ind. Med. 45(5): 313-317.

Chatfield, E.J. (1990). Analytical protocol for determination of asbestos contamination of clothingand other fabrics. Microscope, 38, 221-222.

Chatfield, E.J. (2000) Correlated measurements of airborne asbestos containing particles andsurface dust. : In Advances in Environmental Measurement Methods for Asbestos. ASTM,STP 1342, 378-402, American Society for Testing Materials, 100 Barr Harbor Drive,West Conshohocken, PA 19428. ISBN 0 8031 2616 6.


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Corrigan, C.A. and Blehm, K. (1997). A comparison of tape sampling and micro vacuuming proce-dures for the collection of surface glass fibre contamination. Applied Occupational and En.Hyg., 12, 11 751-755.

Cottrell, S. (2000) HSL FSSU report.

Crankshaw, O.S., Perkins, R.L. and Beard, M.E. (2000). An overview of settled dust analysticalmethods and their relative effectiveness, : In Advances in Environmental MeasurementMethods for Asbestos. ASTM, STP 1342, 350-365, American Society for Testing Materi-als, 100 Barr Harbor Drive, West Conshohocken, PA 19428. ISBN 0 8031 2616 6.

Dost, A.A. (1995). Laboratory assessment of wipe and adhesive sampling methods for particulatesurface contamination’. IR/L/DS/95/1. Health and Safety Laboratory, Broad Lane, UK. S37HQ.

Ewing, W.M. (1992).

Ewing, W.M. (2000). Further observations of asbestos dust in buildings: In Advances in Environ-mental Measurement Methods for Asbestos. ASTM, STP 1342, 403-409, AmericanSociety for Testing Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428.ISBN 0 8031 2616 6.

Fish, B.R., Walker, R.L., Royster, G.W. and Thompson, J.L. (1966). Redispersion of settled dustparticles. In: Proceedings of a symposium held at Gatlinburg, TN. Ed. Fish B.R., Bell andBain Ltd. 75 -83. 1967.

Guth, J.H. (1989) A guide to surface sampling methodology Presented as National AsbestosCouncil, Technical Conference Session No. 8. Interscience Research Inc. 2614 WyomingAvenue. Norfolk. Virginia. 23513

Hays, S.M. (2000) Incorperating dust sampling into the asbestos management program: InAdvances in Environmental Measurement Methods for Asbestos. ASTM, STP 1342,403-409, American Society for Testing Materials, 100 Barr Harbor Drive, West Consho-hocken, PA 19428. ISBN 0 8031 2616 6.

Health and Safety at Work Act 1974, HMSO 1974. ISBN 0 10 543774 3.

HSE, Guidance note EH 10 (1995). Asbestos exposure limits and measurement of airborne dustconcentrations. HSE Books . ISBN 0 7176 1113 2.

HSE, Guidance note EH 51 (1989). Enclosures provided for work with asbestos insulation,coatings and insulation board. HMSO. ISBN 0 11 885408 9.

HSC, L27 Approved Code of Practice (ACoP) for The Control of Asbestos at Work (third edition), HSE Books, London, 1999. (ISBN 0 7176 1673 8).


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HSE, L28 Approved Code of Practice (ACoP) : “Work with Asbestos Insulation, Asbestos Coating and Asbestos Insulating Board" (third edition), HMSO, London, 1999. ISBN 0 7176 1673 8.

HSE, MDHS 39/4 Asbestos Fibres in Air: Light Microscope Methods for use with the Control of Asbestos at Work Regulations. HSE Books 1995, ISBN 0 7176 0913 8

HSE, MDHS 77. Asbestos in Bulk Materials: Sampling and Identification by Polarised Light Microscopy. (ISBN 0 7176 0677 5).

HSE, MDHS 87, Fibres in Air: Guidance on the discrimination between fibre types in samples ofairborne dust on filters using microscopy. HSE Books 1998. ISBN 0 7176-1487-5.

HSE, INDG 288 “Selection of suitable respiratory protective equipment for work with asbestos”. HSE, HSE Books, PO Box 1999, Sudbury, Suffolk. CO10 6FS.

Hurlbut,C.S. and Williams, C.R. (1935) The mineralogy of asbestos dust, Journal of IndustrialHygiene, 17, 289.

IoH, Institute of Occupational Hygienists (1988) Operating code of practice for asbestos clearancecertification. OH, Edinburgh.

International Standards Organisation, (1998) Indoor Air: sampling strategies for the determinationof airborne asbestos and other mineral fibre concentrations. ISO/TC 146/SC6/WG4.

Jaffery, S.A.M.T., Burdett, G.J. and Rood, A.P. (1988) An investigation of airborne asbestosconcentration in two UK buildings: Before, during and after the removal of asbestos. Intern.J. Environmental Studies, 32, 169-180.

Kominsky, J.R., Freyberg, R.W. et al. (1991). AHERA clearance at twenty abatement sites.project summary’. Risk Reduction Engineering Laboratory United States. EnvironmentalProtection Agency, Springfield, Va., NTIS, 1991. 5pp. (EPA/60/S2-91/028).

Kominsky, J.R.; Freyberg, R.W. et al., (1990). observational study of final cleaning and AHERAclearance sampling’, United States. Environmental Protection Agency NTIS, 1990. 7pp. (EPA/600/52-89/047).

Lee, R.J., Van Orden, D.R. and Stewart, I.M. (2000) Dust and airborne concentration-Is there acorrelation. : In Advances in Environmental Measurement Methods for Asbestos. ASTM,STP 1342, 313-322, American Society for Testing Materials, 100 Barr Harbor Drive,West Conshohocken, PA 19428. ISBN 0 8031 2616 6.

Lichtenwalner, C.P. (1992). Evaluation of wipe sampling procedures for elemental surface contami-nation. Am. Ind. Hyg. Assoc. 53, 657-659.


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Millette, J.R., Kremer, T. and Wheeles, R.K. (1990). Settled dust analysis used in assessment ofbuildings containing asbestos, Microscope, 38, 215-220.

Millette, J.R. and Hays, S.M. Settled asbestos dust sampling and analysis. CRC press Inc., 1994.

Millette, J.R. and Mount, M.D. (2000) Application of the ASTM asbestos in dust method D5755. :In Advances in Environmental Measurement Methods for Asbestos. ASTM, STP 1342,366-377, American Society for Testing Materials, 100 Barr Harbor Drive, West Consho-hocken, PA 19428. ISBN 0 8031 2616 6.

Moorcroft, J.S. and Duggan, M.J. (1984). Rate of decline of asbestos fibre concentration in roomair. Ann. Occup. Hyg. 28, 453-457.

Nichols, G. (1985). Scotch Magic Tape - An aid to microscopist for dust examination, The Micro-scope, 33, 247-254,

Oberta, A.F. Manual on asbestos control, removal, management and the visual inspectionprocess.ASTM manual series MNL23, PCN 28-023095-10. American Society forTesting Materials, 1916 Race street, Philadephia, PA 19103.

Oldcrest, R.B. (1987) A radiological technique to quantitate asbestos decontamination. BrujosScientific Inc., 505 Drury Lane, Baltimore, MD 21229.

OSHA (1977) Wipe sampling policies and procedures, Industrial hygiene manual, 115-116,OSHA, Washington D.C.

OSHA, (1995) Occupational exposure to asbestos : Final Rule, 29 CFR Parts 1001, 1915 and1926, Federal register, U.S. Department of labor, Occuapational Safety and Health Admin-istration, 59 FR40964-41162, !0th August, 1994.

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Prentice, J.(1985). Rate of decline of asbestos fibre concentrations in room air. Annals of Occupa-tional Hygiene. vol.29, no.3, 439-440.

Prentice,J. and Webb (1988). Assessment of different dust disturbance techniques at clearancesampling after asbestos treatment. Dept. of Environment Contract PECD7/8/88.

Prentice, J. and Andersen, G. (1990). An investigation into the effectiveness of asbestos manage-ment anf removal programmes in buildings. Mc Crone Research Associates, London

Robbins, M.C. (1980). OSHA’s wipe sampling policies and procedures. sampling and analysis oftoxic organics in the atmosphere. ASTMS STP 721, American Society for Testing Materi-als, 48 -55.


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Rose, V. (1995) Analysis of PCM asbestos air monitoring results for a major abatement project.Paper submitted to OSHA (1995).University of Alabama at Birmingham.

Royster.Jr. G. W. and Fish, B.R. (1966) Techniques for assessing "removable" surface contamina-tion. Proceedings of a symposium held at Gatlinburg, TN. Ed. Fish B.R., Bell and Bain Ltd.75 -83. 1967. 201-207.

Ryan, G., Buchan, R.M., Keefe, T.J. and McCammon, C.S. (1997) An evaluation of the adhesivetape sampling method for estimating surface asbestos concentrations. Appl. Occup. Hyg.,12, 4, 288 - 292.

Sansone, E.B. Redispersion of indoor surface contamination and its implications, In: Treatise onclear surface technology vol 1. Edited by K.L. Mittal. Pleneum publishing Corperation,1987).

Schneider. T., Petersen. O. H., Kildeso. J., Kloch. N. P., Lobner. T., (1995). “Design and Calibra-tion of a Simple Instrument for Measuring Dust on Surfaces in the Indoor Environment.”Indoor Air.

Schneider. T., Petersen. O. H., Eriksen, P and Vinzents, P. (1989). A simple method for themeasurement of dust on surfaces amnd the effectiveness of cleaning. Environment Interna-tional, 15, 5653-566.

Schneider. T., Holm Petersen. O., Aasbjerg Nielsen, A and Windfeld, K. (1990). (1990). Ageostatistical approach to indoor surface sampling strategies. J. Aerosol. Sci. 21,4,555-567, 1990.

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Wheeler, J.P. and Stancliffe, J.D. (1998). Comparison of methods for monitoring solid particulatesurface contamination in the workplace. Ann. Occup. Hyg. 42, 7, 477-488.


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A1. APPENDIX 1: CRITIQUE OF CURRENT CLEARANCE PRACTICE

A1.1. Problems with the current advice.

Current HSE advice in the Approved Code of Practice (ACoP) for work with asbestos insulation,asbestos coating and asbestos insulation board (HSC, L28) refers to site clearance testing as anassessment at the end of a removal to check that the area is fit to be returned to normal occupation.It is described as a two stage process: clearance visual inspection and clearance air monitoring. Theresponsibility for the clearance is placed on the employer of those who carried out the work (usuallythe asbestos removal contractor) must ensure that the enclosure or work area and immediatesurrounding area is thoroughly cleaned and that, “A thorough visual inspection of these areas shouldbe carried out to make sure that all visible traces of asbestos have been removed as far asreasonably practical from the enclosure and the surrounding area.”

Once the work area and immediate surrounding areas have passed a visual inspection, wherereasonably practicable, the contractor is allowed to treat all removable internal enclosure surfaceswith a sealant to reduce the release of residual fibres during air monitoring. The enclosure should bechecked to ensure it is intact and the negative pressure unit switched off and the pre filter cappedand sealed. Clearance air monitoring should be carried out to check that the concentrations ofairborne fibres remaining in the areas affected by the work is as low as reasonably practicable. Theclearance air monitoring should be accompanied by activities which raise dusts from the surfaces, atleast to a level consistent with normal use of the area and possible future work activities. In mostcases it is reasonably practicable to clean the work area thoroughly enough for the airborne fibreconcentration in the work area after the final cleaning to be less than 0.01 f/ml when measured bymethods set out in separate HSE guidance (i.e.MDHS 39/4).

A1.2. Inspector, contractor, client relationships.

In any contractual system there is always a need for an arbiter. Clearly, the basis for an acceptablearbiter is that there is an independence between the contractor responsible for removing andcleaning up the asbestos and the inspector who is responsible for checking this has been achieved.In fact one would expect the inspector to be employed by and working directly for the owner of thebuilding and is ultimately there to ensure and safeguard the asbestos has been fully removed.

Unfortunately, in practice the clearance inspection is far from independent. Often the inspector issubcontracted and paid directly by the asbestos removal contractor. This creates a conflict ofinterest in that the contractor responsible for removing the asbestos employs the person / laboratorywho is supposed to be checking that all the asbestos is removed. The longer the time the inspector ison site and the greater the time taken to clean or re-clean, will be a direct cost to the asbestosremoval contractor. Also the laboratory and the on-site analyst, knows that their likelihood forfurther employment, depends on the opinion of the asbestos removal contractor on how little extracost they incurred. Until recently some of the laboratories or persons carrying out clearance wereactually directly owned or associated with the asbestos removal contractor.


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Even after the latest update of regulation this conflict of interest has not been properly resolved andan external air test is all that is required, as the contractor can carry out their own visual inspectionand collect samples for analysis. The only protection offered to the owner, is a requirement that thelaboratory should be EN 45001 accredited and this accreditation asks that the laboratory does notcarry out work where conflicts of interest may lie.

As most building owners who have an asbestos problem will contact an asbestos removal contractorto request a competitive bid for the work, it is likely the removal contractor will also arrange for theclearance testing. Therefore only a limited number of jobs are overseen by an independent clearanceinspection. The chance of detecting a poor job is minuscule, as few local authority inspectors orHSE inspectors will ever visit the site after the work has been completed. It is therefore left to thesubcontracting tradesman who is refurbishing an area, which has been certified as asbestos free, tochallenge both the building owner and main contractor who are employing him. It also requires thetrades person to have sufficient concern to bring it to the attention of an Inspector (usually at greatpotential cost of time and money to himself and his employers). Clearly, this situation gives only asmall chance of a poor removal job being notified from this source.


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A2. APPENDIX 2: REVIEW OF CURRENT HSE REGULATIONS, ADVICEAND GUIDANCE ON CLEARANCE ASSESSMENT

Somewhat confusingly HSE regulations, approved practice, guidance and advice on clearanceprocedures are set out in several documents: the control of asbestos at work regulations (CAWR1987, amended 1999), two approved codes of practice (ACOP’s L27 & L28 (1999),environmental hygiene notes (EH 10 and EH 51) and methods for determining hazardoussubstances, (MDHS 39/4, MDHS 87). The requirements of the above documents are reviewed.

A2.1. CAWR (amended 1999)

Arguably, many of the difficulties with the current HSE advice stem from the regulation / statutoryinstrument, which was originally designed for the control of the asbestos manufacturing and it hasbeen adapted piecemeal to include asbestos removal and latterly asbestos maintenance. Theregulations have yet to be updated to reflect the situation that the importation of asbestos into theUK (and hence manufacturing) is now prohibited (except for a few special situations). The regulationtherefore has no specific mention of clearance or cleaning after a removal, and the regulation that hasbeen adapted for the purpose Regulation 12 on the duty to prevent the spread of asbestos says,“Every employer shall prevent or, where this is not reasonably practicable, reduce to the lowest levelreasonably practicable, the spread of asbestos from any place where work under his control iscarried out”. The regulation is poorly focused on the problems of leaving a clean environment afterthe removal work and does not give any single duty to remove all the asbestos and clean up allresiduals and debris. The duty is however placed on the employer, where work under his control iscarried out but is ambiguous whether it is the employer of the workers who normally work in thearea, or the employer of the removal workers (i.e. the asbestos removal contractor) who have beenemployed to remove the asbestos. The meaning of, ‘reasonably practicable’, which involves theinfluence of cost, does not in any way mean that all asbestos should be removed and cleaned-up andleaves it open to a very subjective interpretation.

Although the latest amendment of CAWR did not change regulation 12, it introduced a newregulation (15A), that required every employer who requests a laboratory to carry out anymeasurement of the concentration of asbestos fibres present in air, “shall ensure that that laboratoryis accredited by an appropriate body as complying with EN 45001”. If the employer themselves dothe air monitoring they have to meet criteria equivalent to those set out in paragraphs 5.1, 5.2, 5.3and 5.4.1 and 5.4.2 of EN 45001. Therefore for the first time it became necessary to use alaboratory for clearance air monitoring, which complied or was accredited to EN45001. Part ofEN45001 is a requirement that there should be an independence of the laboratory from the asbestosremoval contractor, and for the first time, introduced in the regulations an element of independenceinto the clearance assessment. However, it would be naive to assume that there remains noconnection between some asbestos clearance contractors and laboratories and in any case it isunlikely that any such connections would be apparent. This important but indirect move towardsindependence between the removal contractor and the laboratory is however less certain now thatthe EN45001 accreditation is to be superseded by the new ISO/IEC 17025 standard.


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A2.2. ACoP Procedure for site clearance testing

The poor precision and focus of the regulations for asbestos removal, mean that the ACoP mustinterpret the regulations and set the meaning and standards with which the contractor and the clientshould comply, unless they can demonstrate an equivalence. The ACoP says that,' it is importantthat the enclosure or work area is assessed to determine whether it is fit to be returned to normaloccupation'. The responsibility for the clearance is placed on the employer of those who carried outthe work (usually the asbestos removal contractor). He must ensure that the enclosure or work areaand immediate surrounding areas are thoroughly cleaned and, “A thorough visual inspection of theseareas should be carried out to make sure that all visible traces of asbestos have been removed as faras reasonably practical from the enclosure and the surrounding area.” The ACoP recommends atwo stage assessment: a clearance visual inspection and clearance air monitoring. These proceduresas described by the ACoP are reviewed below.

A2.2.1. Requirement before clearance testing can start

There are a number of important preconditions which should be met before clearance testing can beperformed:

v all the asbestos material and any asbestos-contaminated equipment, clothing etc.inside the enclosure and airlocks should have been removed;

v all surfaces from which the asbestos has been removed should have been thoroughlycleaned;

v there should be no visible debris or dust on surfaces, walkways, work equipment,cable trays etc.;

v the enclosure should be intact.

A2.2.2. Clearance visual inspection

The duty for the clearance inspection is placed on the employer of those who have carried out thework. He must ensure that the enclosure and immediate surrounding area, or work area where anenclosure has not been used are thoroughly cleaned.' A thorough visual inspection should then becarried out to make sure that all visible traces of asbestos and other debris have been removed asfar as is reasonably practicable from the enclosure and the surrounding area.' No advice is givenhow the visual inspection should be conducted.

After the enclosure has been found by the employer to be visually clean it is permitted to spray theplastic surfaces with a sealant to 'lock down' any remaining surface dust on the plastic enclosure.The areas where the asbestos has been removed and the existing plant should not be sprayed withsealant at this point.


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A2.2.3. Preconditions before clearance air monitoring

Following a successful visual clearance inspection but before the enclosure is dismantled, clearanceair monitoring should be carried out to check that the concentration of airborne fibres in the areaaffected by the work is as low as reasonably practicable. There are a number of additionalpreconditions to be met before air monitoring can be carried out:

v the area must have passed a visual inspection and there should be no visibleasbestos materials, asbestos debris or surface dust;

v the area should be dry;

v The negative pressure unit is switched off and the pre-filter sealed.

A2.2.4. Who should carry out air monitoring?

Employers and laboratories can carry out air monitoring. There is only one UK provider of EN45001 accreditation, the United Kingdom Accreditation Service (UKAS), so only laboratories whohave specific accreditation for air sampling and fibre counting analysis by the European ReferenceMethod can technically provide the service. Employers carrying out their own air monitoring shouldmake sure that there own employees carrying out this monitoring receive similar standards oftraining, supervision and quality control to those required by EN45001. (note: EN45001 will besuperceeded by ISO 17025 in 2002).

A2.2.5. Procedure for clearance air monitoring

The air monitoring should be accompanied by activities which raise dust from the surfaces at least toa level consistent with normal use of the area and possible future work activity.

Measures set out in EH10 should be used to determine that airborne fibre concentrations in thework area are less than 0.01 f/ml.

If values of 0.01 f/ml or greater are found an investigation will need to be carried out to discoverthe cause. If the enclosure has not been cleaned properly it will have to be recleaned, visuallyinspected again and re-sampled.

A2.2.6. Interpretation of clearance air monitoring

Clearance monitoring is seen as," a transient indication of site cleanliness, in conjunction with visualinspections and not an acceptable permanent environmental level". PCM monitoring itself is seen asa index of exposure and does not measure all the asbestos fibres that may be present. However,PCM only counts fibres and if other fibre types are present it may overestimate the asbestos fibreconcentration. In some circumstances if fibres are being drawn into the enclosure from outside it maynot be possible to obtain levels below 0.01 f/ml and further investigation is required (MDHS 87).


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A2.3. Guidance on clearance testing EH10

The environmental hygiene note 10 gives additional guidance on site clearance. It identifies clearancemonitoring as the last operation before a site is handed back to the occupiers (this may not be true).It makes the following points:

v the area should be thoroughly cleaned;

v if wet the area should be dried and any residuals removed;

v the removal contractor should make a thorough visual inspection, to ensure that allthe asbestos is removed as far as reasonably practical;

v the client may then want to arrange for a second inspection by a person ororganisation independent of the removal contractor;

v when the visual inspection has shown the site is sufficiently clean and free from allvisible traces of asbestos - the contractor can seal the inner surfaces (but not thestripped surfaces) with a sealant;

v inaccessible creases containing residual surface debris may be sealed with a sealantin exceptional cases,

v the pre-filters to the air movers should be changed, and the unit capped andswitched off,

v If the site is found clean and free from asbestos, clearance air monitoring isundertaken;

v activities designed to raise dust from the surfaces at least to the degree appropriateto any possible future activity in the area;

v while noting there are no standard disturbance techniques, suitable disturbanceactivities are: repeating banging of surfaces with a clipboard, brushing and vigorousdusting;

v a minimum volume of 480 L must be sampled onto one or more filters, with aneffective diameter > 20mm;


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v reassurance sampling can be carried out after enclosure is removed.

A2.4. Guidance on clearance testing EH51

This earlier (1989) guidance in EH 51 is more restricted and recommends:

v the enclosure should be dried and thoroughly cleaned with vacuum cleaners;

v a visual inspection should be made paying attention to areas where asbestos mayaccumulate or be difficult to remove (a list is given in an appendix);

v if clean the inner surfaces of the enclosure can be sprayed with sealant (but not thesurfaces from where the asbestos was removed);

v extraction equipment should be shut- off, cleaned and sealed;

v Air sampling carried out in accordance with ACoP and EH10.

v if asbestos found during the dismantling, further cleaning and air sampling should becarried out;

v limited reassurance sampling in difficult situations.

A2.5. MDHS 39/4

This gives practical guidance, aimed at laboratories, which make PCM air measurements ofasbestos fibres. It repeats the ACOP’s position that clearance air monitoring is, "a transientindication of site cleanliness, in conjunction with visual inspections and not an acceptable permanentenvironmental level ", and should be regarded as a "clearance indicator" and sets a standard ofcleanliness of <0.01 f/ml as measured by the present MDHS. Any variation from the methoddescribed must result in at least as high a standard of cleanliness, and be shown in properlyconducted and fully documented tests.

The MDHS has a number of other measurement strategies which may be applicable to clearance,including:-

background sampling is conducted to establish fibre levels prior to any activity which maylead to airborne asbestos contamination;


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leak (enclosure check) sampling is performed outside the enclosure whilst asbestosremoval work is in progress to check that the environmental control systems are adequate;

assessment of the suitability of respirator protection: this is monitoring insideenclosures whilst asbestos removal is in progress is conducted to assess the effectiveness of dustsuppression measures and the suitability of respiratory protection;

clearance indicator sampling (clearance testing): this requires air monitoring in a cleanedand visually examined enclosure from which asbestos has been removed or encapsulated;

Reassurance sampling: this is monitoring which may be conducted in certaincircumstances (such as when an enclosure has been removed) to confirm that the residual asbestosfibre concentrations are <0.01 f/ml.

MDHS 39/4 for sampling in relation to the clearance indicator, background, leak andreassurance samples uses flow rates of between 1 and 16 litres/min to generate a total samplevolume of 480 litres for each measurement. Sample volumes greater than 480 litres may reduce thefilter area to be counted and pooled samples can be used if below 480 litres.

Clearance indicator sampling should take place only when the enclosure is dry and a visualinspection confirms that it is free from dust. The filter holders should point downwards, be fixed1-2m from the floor and be distributed throughout the enclosure. In tall enclosures (for example,vertical pipe work or lift shafts) samplers should be placed at representative exposure heights,especially in areas where residual dust may be difficult to detect. There should always be at least 2measurements (unless the volume of the enclosure is less than 10m3, in which case 1 measurementis adequate). With that overriding condition, the number of samples should be at least the integer(whole number) next below (A1/3 - 1) where A is determined as follows:

(i) if the enclosure is less than or equal to 3m in height, or in enclosures which are higher than3m but where exposure is likely to be at ground level only, A is the area of the enclosure in squaremetres;

(ii) in other cases A is 1/3 of the enclosure volume in cubic metres; if there are large items ofplant (such as boilers) in the enclosure their volumes may be subtracted from the gross volumesbefore calculating A.

Clearance indicator sampling must be accompanied by activities designed to raise dust from surfacesat least to a degree appropriate to possible future activity in the area. Dust disturbance should beconducted in the vicinity of samplers and in areas where visual inspection or the original siting of theasbestos leads to any suspicion of surface contamination. A suitable activity is repeated hitting ofaccessible surfaces. Other activities may be appropriate: the purpose should be to ensure thatworkers or members of the public using the area in future are not exposed to asbestos unnecessarilyas a result of ineffective cleaning. These dust raising activities should take place for at least 5minutes near the start of each full hour of sampling, or each time a new filter is used in an area. Allequipment used for raising dust should be considered as being contaminated and therefore eithercleaned or disposed of as asbestos waste.


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MDHS 39/4 also gives guidance on how to interpret the results.

A2.6. MDHS 87

This method discusses analytical strategies to identify fibre types to complement the PCM analysiswhich counts but does not identify fibres. This method is important when clearance air monitoringproduces repeated failures and an external source of non-asbestos fibres is suspected.

A2.7. Assessment of HSE advice on clearance assessments

Overall, it is first worth noting that HSE does give a substantial amount of advice on clearance andmuch of it is helpful and relevant. The current ACOPs have an emphasis towards the removal ofasbestos, yet the proposed new duty to manage (CD 159) and earlier HSE advice on managingasbestos in workplace buildings (INDG 223) also recommends remedial actions such asencapsulation and enclosure, where the asbestos remains in place. Also, where only partial removalof ACMs is attempted (e.g. around a valve in pipe work for maintenance activity, or thereplacement of one or two pipes while leaving other pipes intact) it is not clear how the clearanceshould be carried out with some ACMs still intact and an ad- hoc system of conditional removal hasdeveloped.

HSE has no specific regulation to remove asbestos prior to demolition of a building and is onlymentioned in the Approved Code of Practice (see ACoP, L28, paragraph 41) in terms of choosingwork methods which present least risk. This makes it unclear as to what asbestos materials are to beremoved prior to demolition and what standard of clearance is required. There is also widespreadconfusion as to how asbestos removal prior to demolition interfaces with the Special Wasterequirements of the Environment Agency, which currently only applies to waste containing more than0.1 % of asbestos by weight. For instance should vinyl floor tiles and their chrysotile-containingmastic floor adhesive be totally removed from the building before demolition or is it permissible toleave these intact during demolition? It is known that these materials are unlikely to release airbornefibres and will constitute much less than 0.1 % of asbestos by mass of the rubble.

Each of the five published HSE documents dealing with clearance assessment, has a slightly differentstatus or intended audience and with publication dates ranging from 1989 - 1999, reflects a range ofinformation and emphasis, which when viewed together, can result in confusion. Independently, theyall tell only part of the clearance requirements and although cross - referenced, it would not be untilMDHS39/4 was consulted, that it would become apparent that only 5 minutes of dust disturbanceevery hour was required, and that repeated hitting surfaces would be an appropriate activity tosimulate future use. The MDHS however, gives no real advice how this should be done.

There is also potential confusion in the terminology and for instance in the ACoP the assessment maybe referred to as: clearance testing, clearance monitoring and clearance sampling, clearance visualassessment and clearance air monitoring, while MDHS 39/4 talks about clearance indicator


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monitoring. No explicit definitions are given. Clearly HSE’s intention over the last few years torationalise the advice on asbestos into a single package would help the situation. For the purposes ofthis document the assessment in the regulations is referred to as a clearance assessment consisting of a visual assessment and clearance air monitoring. The term ‘assessment’, is already over used inHSE’s asbestos guidance and often appears without a prefix (e.g. assessment and plan of work inthe ACoP, where in this case it means an exposure assessment and/or a risk assessment). Again toavoid confusion a prefix has been used to indicate that a ‘clearance’ assessment required.

Other than the use of the term ‘thorough’, no advice is given on how to make a visual assessment,although an appendix in EH 51, list some of the places where residual asbestos is most likely to befound. HSE advice gives no clear distinction that the visual assessment should first check that theasbestos has been completely removed from the surfaces as detailed in the plan of work. Only whenthis has been achieved should the clean up of dust and debris from the enclosure be carefullyassessed.

The guidance on the use of sealant to, 'lock down', residual materials is also a potential area ofconfusion. A more straightforward message is required. The current HSE approach is that no sealantshould be applied before a visual inspection is passed. Sealant can then be applied to the enclosuresurfaces but not any surface that will remain once the enclosure is removed. The sealents must beallowed to dry before a clearance air monitoring is carried out. Once clearance monitoring is passedthe remaining surfaces can be sealed. This to the asbestos removal contractor is both timeconsuming and often impracticable, if a deadline has to be met. It also carries greater risks of failingthe clearance assessment and the asbestos contractor will reduce his time on site and increase hischances of passing clearance air monitoring if a single all over spray is applied before the clearanceassessment. The end effect, is the same once the enclosure is removed.

A2.8. Recommendations for changes in HSE advice

� A clear duty to remove asbestos, so far as is reasonably practicable, before finaldemolition or major refurbishment should be introduced.

(A debate on whether all asbestos-containing materials should be removed is needed. Forinstance, is it necessary to remove the damp proof course around the base of the building,roofing felt from underneath slates, textured coatings or vinyl floor tiles? How does one do a riskassessment or cost benefit analysis to see if it is or is not, ‘reasonably practicable’?)

� HSE advice on clearance should be combined into a single document and updated toensure a consistent terminology is used.

� Clearance assessment should consist of a number of stages, starting with an initial reviewof what asbestos is present and finishing with a post-clearance assessment.

� More detailed guidance is required on how to carry out a visual assessment and the needto check against the plan of work, should be introduced.


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� A method of clearing an enclosure, although some ACM’s are left intact inside theenclosure, needs to be detailed.

� A method for visual assessment for asbestos debris and surface contamination is needed.

� A detailed method for the type of disturbance, is required.


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A3. APPENDIX 3: LITERATURE REVIEW OF VISUAL ASSESSMENT

A selected survey of other countries’ advice, showed that HSE is not alone amongst regulators ingiving limited guidance on how to carry out a visual assessment. The US which has a highlydeveloped litigation approach to asbestos has been the leader in developing clearance strategies.The US agencies (USEPA, OSHA and NIOSH) all published extensive advice on clearance airmonitoring but only the USEPA’s ‘Purple Book’ (EPA,1985) gave any detailed advice on visualassessment. This still remains the most comprehensive advice published by a US government agencyand is reproduced below.

‘First the inspector should confirm job completeness. If ACM has been removed, substrate surfacesshould be checked to be sure no ACM remains. Special attention should be given to pipes, beamsand irregular surfaces that may have corners and hard to reach areas. If the materials were enclosed,check the areas for tight construction (e.g. no stray drill holes or openings at corners). Inspectencapsulated surfaces to insure that the right amount of sealant has been used; there should be noholes, voids or cracks. Check surfaces behind obstructions (e.g. pipes or ducts) for these signs’.

Next the inspector should determine that the work site has been adequately cleaned. Any activitythat disturbs ACM will release fibres. Therefore work site cleanup after removal, repair, enclosure,or encapsulation is critical.

Examine all surfaces for dust and debris, especially overhead areas like tops of suspended lightfixtures. Use a damp cloth to collect dust from these surfaces and then inspect the cloth for evidenceof dust. This is a practical way to establish that the no dust requirement has been met.’

A more sensitive test for dust is to darken the room and shine a flashlight so that the beam justglances any smooth horizontal surface. Run your finger along the illuminated area. If a line is left onthe surface or if airborne particles shine in the light, dust is still present.

If dust is found by either of the two tests, the entire work area should be recleaned and the testrepeated.’

Further work on site clearance was carried out by the U.S. Environmental Protection Agency(USEPA), in response to the requirements of the Asbestos Hazard Emergency Response Act(AHERA, 1977), which lead to a programme of asbestos management in schools. AlthoughAHERA and the subsequent rule in the Federal Register (40CFRpt 763 part 3) required a thoroughvisual assessment, it did not give a method for this. Two USEPA studies on AHERA clearance(Kominsky et al. 1990 and 1991) tested improved visual assessment protocols and recommendedthe use of white cloths and gloves, as a qualitative method of detecting residual dust deposits.

The AHERA work also prompted an industry association effort to give improved guidance and aNational Asbestos Council task force was set up in 1986, this work was however continued in taskgroup E06.24.03 of the American Society for Testing and Materials (ASTM).


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A3.1. ASTM Approach

ASTM publishes consensus standards which are produced and reviewed on a voluntary basis byinterested participants, in a process that usually takes several years. A number of ASTM committeeshave worked on measurement methods for asbestos and a standard (ASTM, E1368-90) was firstproduced in 1990 and updated in 1995 with the launch of a more detailed manual (ASTM,MNL23) on asbestos, control removal, management and the visual inspection process . These twoASTM documents represents the most comprehensive review and attempt to standardize visualassessment procedures to date. As the committee and author have considerable experience ofmanagement of asbestos projects, their views should be given detailed consideration.

Four aspects of an asbestos removal operation, were identified as requiring visual inspection:

v the extent of ACM within the scope of the work;

v project work performance,

v completeness of removal,

v completeness of clean-up.

A3.2. Extent of ACM within the scope of the work

ASTM E1386 does not regard clearance as an independent procedure to be applied at the end ofthe removal - a more proactive approach to inspection is recommended. The clearance inspectionbegins with the initial building or site survey of ACMs, which locates and identifies the materials tobe removed. This provides answers to questions such as - has the building survey been doneadequately? Is all the asbestos found in the area to be removed? This is important, for if moreasbestos is present than was originally thought, the terms of the contract between the removalcontractor and the building owner will need to be changed. If this additional asbestos is onlydiscovered during the final clearance, or if more asbestos is present than was originally thought, itwill be very difficult to solve the situation, particularly if there is a deadline and time penalties. It issensible to check this before work starts. The removal contractor who has tendered for the work,also has responsibilities in identifying problems, and it is usually to their advantage to find anyadditional asbestos, both from obtaining a clearance, and also for extra payment for removing theadditional asbestos. From the point of view of the building owner, it is useful to have someone tocheck that what the asbestos contractor is contracted and paid to remove, represents all the ACM.

As site conditions may have changed since the original asbestos survey and contract document wasset up, a visual inspection is recommended, before any preparation work starts. For instance,subsequent maintenance work or water penetration may have result in a far greater release andspread of ACM debris and if this is not recognised and cleaned-up before starting to build an


66

enclosure, the site will be left contaminated, even though a perfect removal project was completed.The debris has simply been kept intact and hidden until the enclosure is removed.

Similarly, any ACM material or airborne fibres that can penetrate outside the enclosure may alsoescape detection, until after the contractor has left at the end of the removal.

A3.3. Project work performance

How the work is planned and carried out will largely determine whether residual materials are likelyto remain on the removal surfaces and whether asbestos debris has accumulated inside and outsidethe enclosure. The integrity of the enclosure will need to be maintained during the work and regularinspection will also prevent releases.

Asbestos can leave the enclosure in several ways:

v waterborne;

v airborne;

v on persons, footwear and clothing;

v on contaminated tools and ladders etc.;

v on, or in, sacks.

Asbestos suspended in water and surfactants have considerable abilities to penetrate the enclosure,unless suitable precautions are taken in advance to make sure the enclosure is sufficiently well-builtto contain most foreseeable spillages. Control of the amount of liquid used to remove the asbestos,will reduce the likelihood and amount of contamination that can occur. Surfactants, are particularlygood at penetrating through floors and horizontal joins and seams, and can reduce the effectivenessof adhesive tape. The consequences of water penetration may be to drip asbestos contaminationinto services and trunking and even into occupied areas below, causing extensive additional cleanup.

Airborne releases are minimised by maintaining a negative pressure inside the enclosure andmaintaining the integrity of the enclosure. Any entries and exits from the enclosure for workers andwaste materials are obvious potential routes for airborne leakages, as well as the air being removedfrom the enclosure.

Poor decontamination procedures and facilities also allow asbestos to be removed from theenclosure on a variety of substrates: clothing, footwear, respirators, skin, hair, waste bags, tools and


67

equipment etc. A leaking bag of wet asbestos once outside the enclosure has a significant potentialto contaminate.

The potential for airborne and waterborne asbestos to escape outside the enclosure can be reducedby surveillance during the initial preparation of the work area and by subsequent monitoring duringthe work. This should cover:

1. Construction and adequacy of the enclosure floor and critical barriers;

2. Special isolation requirements, safety issues;

3. Protection of surfaces inside the enclosure;

4. Overall design and build of enclosure;

5. Decontamination facilities;

6. Regular surveillance throughout the removal, to ensure integrity is maintained;

7. Leakage and compliance monitoring during the work;

8. Monitoring water usage, standard of cleaning and debris handling.

A3.4. Inside enclosure

The conditions inside the enclosure will also affect the likelihood and magnitude of any release.Conditions such as:

v the build-up of asbestos debris;

v the over-use of water or spillage;

v keeping large amounts of bagged wastes inside the enclosure;

v failure to clean enclosure on daily basis;

v use of procedures likely to puncture polythene on floor or walls;

v high temperatures (will soften adhesives and lead to seal failures)

will all contribute to a release.


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The floor however is the most vulnerable and this should be constructed from severalnon-permeable layers. Polythene is the usual material of choice but is slippery, particularly whenwet, and relatively easy to puncture. A resistant, disposable non-slip surface, may therefore berequired on top of the polythene. This surface (e.g. hardboard) is removed and disposed of ascontaminated waste as part of the initial site clean-up by the contractor.

A3.5. Completeness of the removal and clean-up

Visible material and debris on the removal surfaces will mean that the site will fail the visual clearanceprocedure. What is meant by visually clean will need to be clearly stated. E1368 suggests that theassessment should be without any magnifying aids. If some materials are to remain after the removal,they must be properly encapsulated or enclosed.

Inspection of all surfaces where the asbestos was removed should be carried out. The inspectorshould be close enough to touch the surfaces and will need to use the contractor’s equipment toaccess high areas. The removal contractor’s supervisor or representative, should accompany theinspector and a worker equipped with appropriate cleaning materials and vacuum equipment. Ifsmall amounts of residual debris are found, these should be cleaned up but if the amount is becominga time consuming final cleaning operation, the inspection should be terminated and a re-cleaning ofthe surface requested.

A range of qualitative techniques to determine whether the removal of residual material is completefrom the removal surfaces and the surface of the enclosure:

v Torch beam,

v Use of white cloth,

v Micro-vacuuming onto a white filter

The use of sharp probes and screwdrivers is advised to look in joins and around fittings on removalsurfaces. Attention should be paid to joins and seals in the enclosure.

A3.6. Completeness of clean-up

All surfaces must be visibly clean before any application of sealant. Often the plastic sheeting frominside the enclosure is sealed and removed before a clearance assessment takes place. Either asecond skin of polythene is present in open areas, or in closed spaces, only the critical barriers overthe doors, windows and vents remain. Therefore clearance largely takes place on clean polythene orthe room surfaces. Various final cleaning methods are used: HEPA vacuuming, tack rags andaggressive cleaning, which are designed to remove any residual fibres from the surface. Aggressivecleaning is used as a final cleaning action and is designed to simulate the disturbance method used


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during clearance air monitoring. In the US this usually means the use of a leaf blower to resuspendany dust. The material made airborne is then collected on the HEPA filter of the negative air unit.

Any signs of leakage should be looked for from the enclosure.

A3.7. Other guidance

OSHA (1995) does not give guidance for visual assessments but stresses the importance of cleaningup after an asbestos removal activity. It does give guidance on how to remove and clean up andstresses the importance of pre cleaning and covering non-removable furnishings and plant. The useof two layers of polythene to form the enclosure (or more) on the floor and the use of encapsulantsto lockdown dust onto the inner polythene sheets followed by their removal, helps ensure that mostof the asbestos dust and debris is removed from the enclosure.

In the UK the Institute of Occupational Hygienists (IoH, 1987) produced a code of practice forclearance monitoring and the British Institute of Occupational Hygienist (BIOH) runs a proficiencymodule P403 on clearance sampling.


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A4. APPENDIX 4: LITERATURE REVIEW OF CLEARANCE AIR MONITORING

A4.1. Review of current regulatory methods.

The UK is similar to many countries in requiring air monitoring as part of the clearance assessment.However, there is a wide range in recommended practices, which makes comparisons very difficult.For instance, in the UK a minimum of two air samples can be collected over a half an hour periodat a flow rate of 16 L/minute, sampling 480 L of air. A minimum of five minutes disturbance activityis carried out at the beginning of the sampling period, with the air extraction system in the enclosureswitched off. Samples are prepared and analysed on-site by clearing the sample filters and carryingout a PCM fibre count. Analytical results are available and a clearance certificate issued some 30minutes after sampling.

In France clearance monitoring is conducted with the air extraction systems left on, over a minimumperiod of 30 hours to collect 10,000 L of air. Initial disturbance of the area is required with the useof fans to keep material suspended. A minimum of two samples are analysed off site using anindirect sample preparation method to ash the filters and resuspend and refilter them onto a differentfilter type, which is then carbon coated and small sections cut out and placed on EM grids beforedissolving in chloroform usually overnight. The samples are then analysed by transmission electronmicroscopy before a decision to re-clean or to take down the enclosure is made.

Clearly the time take for clearance and the costs involved are quite different between the twomethods.

Interestingly, an even greater variety in practice can be seen in the US between different governmentagencies. OSHA did not included a provision for a specific ``clearance level'' in the latest revisedstandards (1995). In reviewing the record, OSHA decided that, ‘there was no clear evidence of alinkage between such a requirement and subsequent lessening of worker exposure. Clearly,regulated areas must be cleaned following asbestos work. However, designation of a specific fiberlevel which must be attained before an area can be reoccupied did not appear to be necessary forworker health when all other provisions of the standard were complied with’. In contrast theEnvironmental Protection Agency in the AHERA (1987) regulations requires extensive airmonitoring on the completion of an abatement action and carries out a TEM analysis at X20,000magnification with 5 samples collected inside the enclosure and 5 samples collected outside theenclosure plus two blanks. The inside and outside results are then compared using a Z-test todetermine whether there is a statistically raised level between the inside and outside air unless theresult are below the limit of detection (>3 asbestos structures counted).

The OSHA position brings into question whether clearance air monitoring requires quite so muchveracity, considering it is a temporary measure of the residual dust that can be made airborne in atemporary enclosure. The French rationale is based on early TEM asbestos mass concentration airmonitoring method used by a Paris laboratory to measure background levels in asbestos-containingbuildings, where a 5 day average exposure was taken. The USEPA method was deemed theminimum necessary by statisticians to tell whether the levels inside the enclosure was significantly


71

different from outside air. The TEM is used because of early work found that fine chrysotile fibreswill not be counted by PCM and few larger >5 um fibres are rarely found in building air. However,from a risk point of view it is only the longer fibres that are likely to present a risk.

A number of other EU countries (e.g. Netherlands, Germany, Austria) use scanning electronmicroscopy (SEM) with energy dispersive x-ray analysis (EDXA) to evaluate the fibres (VDI 3492parts 1 & 2). Although a vehicle portable SEM is now available the method usually requires samplesto be taken or couriered to a laboratory. In practice, SEM analysis offers little more than the PCMmethod in terms of the routine visibility of > 5 um long fibres but does allow limited classification offibre type, which means that some larger non-asbestos fibres can be discounted.

The indoor air sampling strategy being developed by the international standards organisationISO/TC 146/SC6/WG4 includes clearance sampling. This contains little different from HSEguidance but uses a concept of room units to divide up larger areas and to decide the number ofsamples required.

The current UK approach of using PCM as a clearance indicator seems to be both a sensible andefficient approach to check that airborne concentrations inside the enclosure are low before it can betaken down.

A4.2. Site studies

Karrafa et al.(1984), reported on an early EPA-funded study on the clearance of a site after theremoval of chrysotile sprayed fireproofing. Air sampling was carried out after polythene had beenremoved and surfaces sprayed with a sealant. Both static (no disturbance of surfaces) andaggressive sampling (a 1 hp leaf blower was used to sweep all surfaces every hour during a 8 hoursampling period), were compared along with PCM and TEM analysis of fibre concentrations fibrecounts to static was 3.4 for PCM and 6.3 TEM, average PCM concentrations during aggressivesampling were 30 f/L.

9.85.26.5Ratio TEM/PCM7256415TEM (S/L)2664213TEM (f/L)2782PCM (f/L)

Post abatementaggressive

Post abatement staticOutdoorAnaltical techniqueTable A1: Early EPA results for different methods of clearance testing.

Bailey et al. (1988) reported personal measurements on analysts from 100 routine clearanceassessments, which had an average sampling time of 39 minutes (range 5 -194 minutes). The highestvalue obtained was 0.4 f/ml with a group mean of 0.04 f/ml with a 4 hour time weighted average of<0.01 f/ml. Half of the individual samples were over 0.01 f/ml. The average 12 week work periodwas calculated as unlikely to exceed 4.8 f -h/ml, well within the action level and led to therecommendation that respirators with a nominal factor of 10 could be used.


72

Burdett (1988), evaluated aggressive sampling methods and decay times at a large multi-storey sitecontaminated with crocidolite after a poor removal action (shot blasting was used to removesprayed crocidolite from steel beams) repeated lock down using sealents had been attempted.Various types of disturbance sampling (compressed air blowing, sweeping and dusting) and werecompared using different a 10 m x 10 m test areas on different floors. Background samples with nodisturbance gave TEM concentration of >5 um long fibres of 1 f/L. As four of the five samples takengave fibre counts above the LOD (4 fibres) this was seen to represent a low residual concentration.Short term and long term samples were taken to measure the rate of decline of fibre levels afterdisturbance. The use of different areas meant that there was no way of knowing if a uniform amountof fibre was present and it was concluded that it was perhaps more important to disturb all thesurfaces (as small pockets of asbestos probably occur), than to be too concerned about the methodof disturbance. Two different areas disturbed using a compressed air line gave 7 and 2430 f/Lrespectively. It was not possible to directly compare the effectiveness of different disturbancemethods from the TEM study. Short term (30 minute) samples were used to monitor decay rate butsome air movement in building due to wind pressure may have increased the dilution. Increases inthe period directly after the disturbance were found, compared with during the disturbancesuggesting that there was a peak at the end of the disturbance period (approx. 30 minutes). A goodcorrelation between PCM and TEM counts were found, with about 3 times as many >5 um longTEM fibres seen.

Prentice and Webb (1988) used the same site to assessment of different dust disturbance techniquesusing 4 operators and four disturbance methods. Each operator used all four methods on different100 m2 areas close to each other. The results given in table A2 show that a comparison of the fourmethods on the same floor by the same operator, consistently gave compressed air as the mostefficient dust resuspension method. However, there is no guarantee that the area concentrationswere the same.

100670compressed air

1.510clipboard

640duster1.510BroomC

10050compressed air *

6030clipboard

10050duster

2010Broom

B

10090compressed air

22.220clipboard

55.650duster22.220BroomA

% of compressed airArea average (f/L)MethodOperatorTable A2: Results from comparisons of different disturbance methods at a test site.


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* Compressed air bottle ran out and only 2/3rds of resuspension time achieved.100557.5compressed air

25.175clipboard

41.145duster11.315BroomAll

1001,420compressed air

16.9240clipboard

2.840duster1.420BroomD

As there was no knowledge of the actual amount of contamination present in each test area it isdifficult to draw detailed comparisons. However, the compressed air consistently gave the highestairborne levels and appeared to be by far the most efficient method to re-entrain settled asbestosfibres. The duster was the next highest with the clipboard and broom giving lower results. It wasfelt that the smooth surfaces may have increased the amount of asbestos made airborne by blowingand the broom in particular suspended larger particles which may have reduced the fibre counts.

Booker and Purnell (1990), reported on removals from 12 sites, mostly AIB. One site was followedpost abatement and had measurable levels 1, 49 and 184 days post removal. It was concluded thefibres had been trapped underneath the enclosure in a carpet, no pre cleaning or post-cleaning wasdone. Five out of 11 sites showed post removal increases, ‘even though all the removal sites hadbeen cleaned to a high standard and on no occasion was asbestos debris found in what wasformerly the work area,’

Kominsky et al. (1991), reported on 20 school clearance sites to evaluate the AHERA protocol.Thirteen sites had sprayed insulation and 8 sites had thermal (pipe and boiler) insulation. Chrysotileonly was present at 17 sites, 2 sites had amosite and one site had both chrysotile and amosite. Theclearance assessment took place after the polythene tent was taken down but with the criticalbarriers still in place and the air extraction on. All sites were subject to a rigorous final cleaningwhich usually included vacuuming and wiping surfaces and mopping floors. The first visualassessment was carried out by the on-site technician representing the school board, 2 of the 20 sitespassed first time and 18 passed the second time, after recleaning. A separate visual inspection wasthen carried out by New Jerseys Dept. of Health Asbestos Control Service at 15 of the sites. Only1 site passed first time, 5 the second time and 4 each for the third and fourth time. The final siterequired 7 inspections to pass. The most common reason for failure (8 sites) was the presence ofdebris on pipes, pipe fittings and hangers. The next most common reason was the presence of debrison floors and horizontal surfaces. When suspect dust or debris was found by the inspectors asample was taken for bulk analysis and asbestos was present in approximately 90% of the samplestaken.

Clearance air monitoring was conducted at 18 sites using the AHERA procedure of aggressivesampling using 1 hp leaf blowers to resuspend the dust and stationary fans to keep the dustsuspended. It was found that 14 sites failed to meet the required amount of disturbance (5 minutesof leaf blowing for every 1000 square feet). Samples were analysed using the TEM AHERAprotocol. Fourteen sites were found to pass the AHERA clearance air monitoring first time, three


74

the second time. Only one site failed AHERA TEM clearance after passing the second thoroughvisual inspection.

Information supplied to OSHA (Rose, 1995) in which over 2000 sampling results were presented,taken over a five year period during which thermal system insulation was removed from a singlebuilding. This study provides very extensive data on closely observed work which the authorsdescribed as near ideal conditions existed to support the proper abatement of ACM are given intable A3.

0.005 - 0.0080.00694Mini-enclosure-clearance0.002-0.0030.002161Full enclosure-clearance0.025 - 0.0310.02386Glovebag- background0.034 - 0.0410.03430A glove bag0.13-0.0580.0238Mini-enclosure-background

0.016 - 0.0360.0235Mini-enclosure-entrance0.01 - 0.0250.02333Full enclosure-background0.021 - 0.0330.02303Full enclosure-entrance

95% Confidenceinterval

MeanConcentration (f/ml)

Number of samplesSample DescriptionTable A3: Data Supplied to OSHA

A4.3. Methods of dust disturbance

Generally, all clearance monitoring methods use some form of dust disturbance to make the settleddust fibres airborne. Again in the guidance, a wide range of dust disturbance methods are used.There appear to be two types of disturbances: those which are chosen to simulate a worst casedisturbance, or those which are used to simulate a representative routine disturbance. The worstcase is usually based on a leaf blower, while representative disturbance is much less standardisedand can vary from routine cleaning activities (e.g. sweeping with brushes or brooms and dusting) tomore vigorous play activities (e.g. bouncing balls and slamming doors). In some situations, activitieswhich are easier for sampling personnel to perform, as they only require equipment which is on hand(e.g. striking surfaces with clip boards, waving unused asbestos sacks in the air) have been adopted,more for convenience than their being representative of future disturbance activities.

The time and extent of the disturbance activity recommended also appears to be designed more foranalysts’ benefit, rather than as a representative future activities. For instance, most cleaners may beexpect to sweep or vacuum for more than 5 minutes, which is the period of time recommended byHSE for the disturbance procedures. Also, standard disturbance times do not take into account thesize of the enclosure and 5 minutes disturbance in a 25 m2 enclosure is unlikely to have a similardisturbance efficiency when used in a 2500 m2 enclosure.


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A4.4. Effectiveness of dust disturbance

A leaf blower appears to be the most efficient way to disturb a large (flat and non-flat) surface area.Whether particles are resuspended, or with what efficiency, is however dependent on the surface airvelocity, which will decrease rapidly with increasing distance between the outlet nozzle and thesurface. Therefore there is a balance to be struck, between the uniformity and the versatility of thedisturbance method and the size of the area to be disturbed Additionally, there is also a requirementthat the disturbance is not only sufficient to raise dust but there is an effective method for mixing anddistributing it inside the enclosure. A leaf blower has a high ability to suspended and mix the dustwith other air. A broom has much less of an ability and gives a more localised dust cloud. Somemethods recommend the use of mixing fans in larger enclosures or when sampling takes place over aprolonged period (e.g. USEPA and France) One possible compromise, is to use a (filter-less)vacuum cleaner with a floor brush head, which offers both a physical disturbance and standard airflow conditions across a flat surface, coupled with an effective air mixing system.

However, while seeking more efficient disturbance methods, account must be taken of the increasedrisk to the sampling personnel from the higher exposures generated. Also, whether the emissions canbe contained without the operation of the air extraction and the availability of a power supply arealso important considerations.

A4.5. Time of sampling

The time of sampling will affect the concentration measured. Fibres will settle out or be subject tointerception or electrostatic attraction effects in an enclosure. They may also be dilution effects to airexchange. These should be minimal at sites where the air extraction is switched off and sealed but insome countries where it is left running, five or six air changes per hour can be expected. In anunventilated enclosure fibre can be expected to settle out at a rate based on their aerodynamicdiameter, which is largely dependent on the fibre width / diameter and length and angle of fall areminor influences. Amosite usually generates the largest mean fibre widths and a 0.4 um fibre willsettle out at a rate of about 0.01 cm.sec-1 and chrysotile and crocidolite usually have small meanfibre widths 0.1 - 0.2 which will settle at a rate of < 0.001 cm.sec-1, or about 1 m.day-1. At theselow rates of sedimentation, the fibres are more likely to be removed by air exchange, diffusion,interception and electrostatic effects. The actual concentration measured will depend on the degreeof disturbance and mixing used to suspend particles. If a broom or brush is used, the disturbancemay not be particularly good at mixing the fibres and the use of fans should be considered. Eachasbestos disturbance method will produce different results.

In practice, it can be expected that airborne fibre concentrations will tend to reduce exponentiallywith time, depending on a number of factors. One important factor is the type of disturbance andactual measurements of the concentration are the best indicator to setting an appropriate samplingperiod. There are relatively few measurements in the literature of the rate of decline of asbestosfibre levels. Moorcroft and Duggan (1984) noted that in a sequence of three 1 hour samples takenbefore, during and after a period of disturbance for clearance air monitoring, that the fibreconcentrations returned close to the before levels sooner than would be expected from thegravitational settlement. They calculated that a drop in level during the third period of samplingshould be by less than a half but the measured values were reductions by factors of 2 - 15. It was


76

thought air exchange rates could not account for this and interception and electrostatic attractionwere thought to be increasing the removal of particles from the air. Prentice (1985) also observedthat particle concentrations on the surface of clearance filters rarely increased after sampling longerthan 80 minutes suggesting that fibres made airborne readily settle out and longer sampling periodsmerely reduce the calculated airborne fibre concentration.

Two unpublished reports also measured the rate of decline of measured concentration with timeduring clearance air monitoring. Burdett (1988) measured concentration v time in a series ofexperiments at a large removal site contaminated with crocidolite. The site was very large and 10 m2

areas were marked out for disturbance. No polythene containment was present and some airmovement through the large floor area due to wind pressure was noted. Samples were taken atapproximately 30 minute intervals during and after disturbance. It was found that with compressedair and dusting the 30 minute period immediately after disturbance gave the highest airborne levels,while the broom decreased immediately after disturbance. The amount of decrease in the 30 minuteperiod was about 66% for the compressed air and broom and about 20% for the duster. Thevariation between different disturbance methods made developing a predictive model difficult.

Ewing et al. (1992) measured the decline of chrysotile concentrations at eight separate abatementsites. The enclosures were reported to be well-sealed to give minimal air movement duringmaintenance and custodial activities but information about the size of the enclosure was given. Eachsite was sampled during the disturbance and one time interval (21 - 1155 minutes) after thedisturbance. Four to six samples were taken for each time point and the geometric mean calculated.Various sizes of structures were measured by the TEM analyses and were used to calculate the rateof decline of different fibre sizes, by plotting the percentage decrease in the initial airborneconcentration with each sample site. The data was described by a decay function of the form y =x/(1+t2 ): where x = mean airborne concentration, t = settling time (hours) and y = airborneconcentration after time t. This function gave a good correlation to the data, e.g. for >5 um longfibres the correlation coefficient was 0.98 (slope = 1.14 and intercept = -0.06). The two studieswere carried out under different conditions and with different fibre types and levels and types ofdisturbance but conclude that after about 1 hour after disturbance the concentration is about half ofthe highest value and longer sampling periods will only further underestimate the peak values.

There is no data for amosite asbestos which is likely to settle out at a faster rate, or the effect ofsmall enclosures with polythene sheeting.

A4.6. Post - Clearance Reassurance Monitoring

The efficiency and performance of different clearance air monitoring measurement methods becomesless of an issue, when it is considered that it is merely an indicator that it’s safe to take down theenclosure. Additional fibres may be released from covered debris and dust, which has been trappedunder the enclosure or has penetrated through the enclosure. However, it is extremely rare to sampleduring the removal of the enclosure or after the removal workers have left the site. Increasedairborne asbestos levels have been reported after asbestos removal when further maintenance work,refurbishment work and even during normal occupation, by a number of studies. A review anddetailed examples of two sites were reported by Jaffery et al. 1988. It was also documented that


77

when post removal disturbance sampling was used, the fine asbestos dust remaining, could if sweptwith a broom, easily exceed the clearance level and approach the 4 hour control limit.

It would therefore seem important to carry out a further assessment, after the enclosure has beenremoved but before reoccupation is allowed. This ‘reoccupation’ assessment would confirm that thesite is left clean, and the levels of asbestos debris and fine asbestos dust are low, even if the surfacesare disturbed. This would provide extra reassurance to the building user or owner, that all the moneyspent on removal has achieved the objective of reducing the risk.


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A5. APPENDIX 5: REVIEW OF SURFACE DUST SAMPLING METHODS

A5.1. Types of method

Sampling of settled dusts and fibres from surfaces has been widely practiced and various methodshave been described in the literature:

� excision sampling;

� scrape or brush sampling deposits into a suitable container;

� wipe sampling with a suitable substrate and liquid;

� adhesive tape sampling;

� strippable film sampling;

� vacuum/ pump sampling;

� air disturbance sampling.

Excision sampling is used mainly for sampling contaminated carpets (Wilmoth and Chatfield) andmay be used before or after a removal if a carpet is left in place under the polythene floor. Scrape orbrush sampling into a suitable container was the original method used to collect settled asbestos anddust from horizontal surfaces (Hurlbut and Williams, 1935). Another method is to use a sealableplastic bag, which first turned inside out and placed over the hand and drawn along the dust and thenreversed. Surface wipe sampling using a suitable filter substrate has also been widely used to collectsurface dust samples. Often a liquid is used to give improved pickup of the dust and multipleimpressions over a surface are taken to give a more representative sample on the filter (OSHA,Robbins 1980). Adhesive materials offer a better chance of picking up dust and the use ofhousehold tapes such as ‘Sellotape’ and ‘Scotch tape’ (Nichols, 1985, Ryan et al, 1997, Corriganand Blehm, 1997), Adhesive foils (Scheider, 1990), ‘Post-it’ notes (Millette, 1990) as well asforensic tapes (Ryan, 1997) have been used by various authors. A more efficient pickup of dustfrom rough surfaces can be achieved by using sprayed films which penetrate into the surface andthen set and can be peeled away. A direct pickup into a filter cassette (Royster and Fish, 1966) andby micro vacuuming the area has been described and standardised (ASTM method D5755).Indirect surface sampling is achieved by disturbance sampling and collecting the airborne dustgenerated, as used for clearance sampling at asbestos removal sites.

A5.2. Sampling variables

Although, all these techniques may prove to be useful, they will all have different collectionefficiencies and be influenced by a number of variables. The variables are of three types:


79

� variables associated with the surface (e.g. surface roughness, porosity, area sampled);

� variables associated with the contaminant (e.g. concentration, particle size, shape and density);

� variables inherent in the sampling procedure (e.g. for wipe sampling nature of wipe material, thesolvent used, the pressure applied, personal variations).

A5.3. Quantitative investigation - radioactive assessments

Several authors have compared the efficiency of different surface sampling techniques on a variety ofsurfaces. As microscopical evaluation of particle or fibre number is difficult to quantitate and haspoor precision, studies using radioactive dusts have been examined first. Royster and Fish used ~ 1um thorium dioxide particles on various surfaces (e.g. Polythene, glass, stainless steel, fibre board,floor tile and concrete) to test a filter wipe method, an adhesive paper method and a filter cassettemethod based on an adapted filter head (Smair sampler). The adhesive paper proved the mostefficient sampling method with 54.8 - 86 % of the dust sampled. The wipe sample collectedbetween 23.5 - 70.6% and the Smair sampler collected between 6.6% - 33%. Various surfacefinishes were also investigated and greased concrete gave the lowest pickup (excluded from theranges above) while waxed or painted surfaces increased the pick up. It was noted that the samplingefficiency of the adhesive paper, was correlated to the surface roughness and the sampling / removalefficiency of the Smair sampler increased with increasing air velocity and increasing particle size. Forinstance the Smair sampler used with velocities of less than 20 m/sec for 0.5 um particles removed<10% of particles, but when operated at 50 m/sec removed some 50% of the particles. This findingis also important when considering dust disturbance methods.

Oldcrest used neutron activated UICC chrysotile which was then applied to a variety of surfaces.The amount of gamma radiation was measured before and after the removal method to calculate thesampling efficiency and precision of various methods (see table A4).

86 (27)88.9096.5178.0694.364.05Wet

54 (2)63.29(17.2)

75.69(7.1)

86.00(13.2)

23.4(13.2)

2.02(2.9)

Scotch tape

15 (21)79.33(17.0)

82.83(5.4)

60.98(27.7)

51.11(7.0)

21.72(24)

High HEPAvacuum

95 (5)74.71(24.0)

86.81(6.3)

86.17(4.9)

95.25(3.4)

76.99(9.3)

Spray polywall type

100 (5.0)69.36(3.4)

85.9(11.4)

75.56(12.1)

95.52(6.3)

70.9(0.4)

Spray polyfloor type

Pyrexglass

Vinylfloor tile

Ceramictile

Pine woodred claybrick

Cinderblock

Removalmethod

Table A4: Results on collection efficiency of irradiated chrysotile on varioussubstrates. (average and standard deviation, based on 5 repeats).


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(3.3)(4.8)(4.0)(0.2)(5.7)polyurethanesponge

This quantitative data shows that both the cleaning and sampling are surface dependent. In terms ofdecontaminating a site if very rough surfaces are left uncovered inside the enclosure during theremoval or becomes contaminated, the HEPA vacuum and wet wipe methods will be relativelyineffective. However, wood and bricks appear to be cleanable by conventional methods.

A5.4. Whole surface analysis

Dost (1997) used an x ray fluorescent method to look at the sampling efficiency of wipe andadhesive sampling methods on a variety of surfaces containing different sizes and concentrations oflead oxide particles. Discs of material ( aluminium, perspex, silicon) as well as aluminium andplywood sheets were exposed to the lead aerosol and the amount of lead measured before and aftersampling to calculate the sampling efficiency. Wipe samples were collected with moistenedWhatman 540 filter papers wrapped around a glass rod, single wipes and multiple wipes over a totalarea of 100cm2 area were used along with Sellotape and forensic tape sampling. Wipe sampleswere seen to give improved efficiency and precision with increased pressure and repeated samplingfrom the same area. However, particle size, surface type and roughness and contamination level allhad substantial effects on the sampling efficiency. For adhesive tapes the particle concentration andsurface roughness had little effect and a good sampling efficiency and reproducibility was obtained,except for the very rough materials and was recommended as the preferred method for surfacesampling. Selotape was less effective. Field trials of various wipe methods (OSHA filter method,and adhesive tape methods were reported by Wheeler and Stancliffe, (1998) at 5 locations tosample lead processing, steel mills and one welding facility. Various surfaces were tested (e.g.Formica, vinyl floor tiles and painted surfaces). Adhesive tape methods were found to be the mostefficient and consistent method for surface sampling. The OSHA filter method was the least effectivemethod for wipe sampling and wet VDU wipes were the most efficient. No improvement usingsemi-automated sampling methods were found. The Smair sampler was the most inefficient methodoverall.

A5.5. Quantitative asbestos specific methods

In recent years surface sampling of fibres has been increasingly used for investigating contaminationlevels in buildings with asbestos containing materials (Millette et al. 1990; Hays, 2000). Much of thework was driven by US litigation strategy as the ambient measurements of airborne asbestos in thebuildings were generally the same as the urban background. The low levels of airborne fibres didhelp the case of the building owners who were attempting to prove a risk, so two types of samplingwere introduced; simulated disturbance sampling and surface dust sampling, to give higher numbers.Simulated disturbance sampling involves carrying out actions, which disturbs the asbestos materialdirectly (e.g. simulated maintenance work) or the surface dust (which may have accumulated overmany years or just a few days since the last cleaning). Surface dust sampling is used to argue that theasbestos in the building is a significant risk, firstly as the asbestos must have been released and been


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airborne to get to the surface and secondly now it is on the surface it can be resuspended and madeairborne again.

Many methods of surface dust sampling for asbestos have been used but two ASTM proceduresD5755 and D5756 for analysis of asbestos structure numbers (S/cm2) and asbestos mass (g/cm2)were the first to be developed and agreed by the various interested parties. The D5755 method isnow claimed to be in widespread use in the US (Millette and Mount, 2000) and this usage has foundthat a general background of <10,000 S/cm2 is present with levels above 100, 000 S/cm2 beingconsidered as high (Millette and Hays, 1994). Some authors (Eking, 2000) also consider a level of<1000 S/cm2 as ‘clean’.

However, it is important to recognize that both of the micro-vacuum methods are indirect andsuspend the dust in water, which can have a substantial influence on the fibre number, as solublecomponents of the matrix will dissolve and the shaking and ultrasonic treatment breaks up andreleases fibres (Chatfield, 2000). Various attempts have been made to estimate what the airconcentration might have been to give rise to the surface level found or to estimate what the airconcentration may be if it is disturbed. However, both of these approaches do not take account ofthe fact that the size distributions in settled dust and airborne dust differ substantially, as does theability of particles to be resuspended (Sansone, 1967, Chatfield, 2000). In practice, all sizes ofasbestos debris can be produced and may well not be inhalable, so indirect surface dust methodsare difficult to interpret. When the correlation between surface dust and airborne concentration havebeen examined, Lee at al. (2000), no correlation was found. Also, the samples taken may not berepresentative of the spatial distribution (Schnieder et al. 1991) of asbestos fibres elsewhere in thebuilding.

Other ASTM standards for tape lift and passive sampling are also under development.

A5.6. Recommended methods for surface dust sampling

Direct tape lift methods, which do not significantly alter the particle size distribution, give a bettermeasure of the amount of asbestos present and can be used to investigate the level of fibrecontamination. However, the sampling efficiency is surface dependent and the sample itselfrepresents an even smaller sampled area than micro-vacuuming. Therefore, while tape lift samplesanalysed by PCM for surface fibre concentrations can provide some useful measurement informationthe spatial variability is a problem and disturbance air monitoring which is designed to loft the settledfibres gives a better estimate of whether the surface contamination is a problem.

A visual surface dust assessment, of the dust collected on a white surface is probably all that isrequired for clearance sampling and only when assessing the site before or after the removal, woulda quantitative assessment be necessary. Various wipe methods have been described.


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A6. APPENDIX 6: SITE SAMPLING AND OBSERVATIONS

A6.1. Site A

AIB ceiling tiles containing amosite were removed from a store room on the first floor of a sportscentre. The enclosure consisted of two small square shaped rooms and was a maximum of 8 m2 but< 24 m3. A 3 stage air lock was attached to the door and the walls inside were covered in plastic.This lead to the main enclosure, the floor of which was covered with tiles and left unprotected. Theinner room had white wall and floor tiles. The analyst examined the area thoroughly using a torch butthe walls of the enclosure were visibly dirt. This was the first visit and not all the tests developedwere performed.

Wipe Test:- Both the walls and the floor failed this test producing a visible mark in 10 cm. Theresults are listed in the table below:

Visible dirtOuter room floorNot visible in 10 cm but visible in 20 cmOuter room wallDense visible dirtInner room floorVisible mark less dense than floor wipeInner room wallMedical and Whatman Filter WipesLocation

Results suggest that no attempt was made to clean the enclosure properly indicate than the floor wasmore dirty than the walls.

Torch Test:- The torch placed at an angle to the surface highlighted a lot of dirt on the plasticsheeting in the hallway. I was informed that this was not ‘locked down’ with PVA solution. Althoughthe air lock was well maintained and in good condition it was visibly dirty. However, the tiled floorof the inner room appeared relatively clean.

Vacuum Samples:- Sample taken from plastic wall gave a result of 1.9 f/mm2 that is equivalent to0.072 f/mm2 on the plastic surface. The floor gave a result of 65.6 f/mm2 that is equivalent to asurface concentration of 0.24 f/mm2.

Disturbance Test:- The air mover was sealed and the analyst wipes all surfaces at eye level with acloth for 5 minutes, but made no attempt to disturb the floor area. The HSL clearance involvedbrushing the floor for 5 minutes and the air was sampled for 60 minutes.

A6.2. Site B

The basement boiler room underneath a church had continually become flooded by a natural springand lagging attached to a boiler had become saturated with water and had disintegrated. Theworkmen were charged with removing the asbestos and had removed the boiler with any remainingasbestos. A 3 stage air lock was situated at the top of the stairs leading to the boiler. The whole area


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was segregated into two separate areas by a brick wall each about 5 x 5 m and about 4 m high.The total area of the basement was not more than 50 m2. One area was where the boiler had beensituated and the other was a more general area. The area where the boiler was situated was almosttotally covered by a water about 2 -3 cm deep in places. The floor area and walls of the other areawas also visibly wet. A sample of water taken at the site indicated the presence of about 4940fibres/ml. The analyst conducted a very thorough visual survey using a torch to examine areas.However, the area was visibly dirty with general dirt that had settled at the bottom of the pools.

Wipe Test:- Wipe test on the brick produced a visible mark in 10 cm.

Torch Test:- The area was so visibly dirty that there was no purpose in using the torch test.

Vacuum Samples:- Sample taken from a brick wall that had formed one of the supports for the oldboiler gave a result of 3.6 f/mm2 that is equivalent to 0.13 f/mm2.

Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes byfilling a large plastic sack with air and hitting the walls with the inflated sack. The HSL clearanceinvolved brushing the walls for 5 minutes and the air was sampled for 30 minutes.

A6.3. Site C

This site was located at a residential garage where ceiling AIB boards had been removed. The 3stage air lock was situated outside a door to the garage. Plastic covered the inside of the maingarage door and some other items that had remained inside during the removal. The floor area wasunprotected. All walls and plastic had been sprayed with PVA and small pools of wet PVAremained at the bottom of the plastic covering the garage door area.

Wipe Test:- Wipe test on the floor, ceramic tiled window sill and plastic covering some itemsremaining in the garage produced a visible mark in 10 cm. Although the wipe test produced only afaint mark on the window sill.

Torch Test:- The area was so visibly dirty that there was no purpose in using the torch test. Thetorch would not be able to distinguish the grave like concrete floor of the garage from other dirt.

Vacuum Samples:- These samples were too heavily loaded to provide a meaningful count.

Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes hitting the walls with a clip board. The HSL clearance involved brushing the floor for 5 minutes andthe air was sampled for 60 minutes.

A6.4. Site D

A enclosure was established outside to remove AIB boards containing amosite from windows at afarm house in Derbyshire. The enclosure was about 4.5 x 1.5 x 3 meters high. Wet PVA solutionremained in small puddles inside the enclosure. The floor area and walls were protected with a


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plastic covering. The analyst conducted a through visual assessment using a torch and calibrated hispumps corrected for temperature and pressure inside the enclosure. Some MMMF insulationremained in place along the top edge of the window sill. The analyst was cautious not to disturb thisarea during his air test.

Wipe Test:- Wipe test on the stone window sill and plastic covered floor produced a visible mark in10 cm.

Torch Test:- This was not practical as too much wet PVA remained on the plastic and the brickand concrete walls made it difficult to distinguish clean areas.

Vacuum Samples:- The sample on the floor gave a results of 18.56 f/mm2 on the filter whichequates to 0.69 f/mm2 on the surface and the sample on the window ledge gave a result of 44f/mm2 that equates to 1.26 f/mm2 on the ledge surface.

Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes byhitting the walls and plastic with a clip board. The HSL clearance involved brushing surfaces for 5minutes and the air was sampled for 30 minutes.

A6.5. Site E

Ceiling tiles were removed from a fire station in a area where the vehicles would usually be parked.The enclosure was about 30 x 20 x 6 m high and stretched from the floor to the roof. The ceilingtiles containing amosite had been attached to a grid like frame work. The analyst made a carefulexamination of the grid like framework that supported the asbestos boards vacuumed a largeproportion of the grids and knocking down some residual debris to the floor. The floor was coveredwith polished concrete that was smooth and visibly dirt even though it had been mopped andvacuumed.

Wipe Test:- Wipe test on the floor, shelf and window sill produced a visible mark in 10 cm. Thissuggests that mopping and vacuum cleaning combined are not particularly effective methods ofcleaning.

Torch Test:- Floor was visibly dirty.

Vacuum Samples:- The highest of the two samples from the floor gave a result of 32.76 f/mm2 onthe filter which equates to 1.2 f/mm2 on the surface. A sample from a shelf gave a result of 5.9f/mm2 which equates to 0.19 f/mm2 on the surface and a sample from the window sill gave a resultsof 18.1 f/mm2 which equates to a result of 0.69 f/mm2 on the surface.

Adhesive tape Samples:- Samples taken directly from the surface indicated between 206.3 and126.1 f/mm2 on the floor, between 14.3 and 29.7 f/mm2 on the shelf and 40.7 f/mm2 on thewindow sill.


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Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes byshaking a plastic bag in the air. The HSL clearance involved brushing surfaces for 15 minutes andthe air was sampled for 30 minutes.

A6.6. Site F

Asbestos board (AIB) containing amosite was removed from a kitchen in a public building. Theenclosure was about 84 m3 and included the area around the fryer. The area was enclosed withplastic, supported from the floor to the ceiling with wood, but the floor and cooking equipment wasnot protected from falling debris or inadvertent contamination. The analyst made a carefulexamination of the area where the asbestos had been present and removed any suspectcontamination using a H type vacuum cleaner. The floor was tiled and the smooth metal lids coveredthe fryers.

Wipe Test:- Wipe test on the floor, produced a visible mark in 10 cm.

Torch Test:- Visible contamination was only apparent on the plastic surface of the enclosure.

Vacuum Samples:- A sample from the floor gave a result of 3.02 f/mm2 on the filter which equatesto 0.12 f/mm2 on the surface. A sample from the grill gave a result of 0.92 f/mm2 which equates to0.03 f/mm2 on the surface and a sample from the air mover unit gave a result of 0.63 f/mm2 whichequates to a result of 0.02 f/mm2 on the surface.

Adhesive tape Samples:- Samples taken directly from the surface indicated between 108.1, 85.5and 81.5 f/mm2 on the floor, 202.7 f/mm2 on the fryer, 0.8 f/mm2 on the horizontal surface of atiled wall and 0.2 f/mm2 on the plastic sheeting.

Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes byshaking a plastic bag in the air, making no attempt to disturb the floor area where the adhesive taperesults indicate the majority of the free fibres rest. The HSL clearance involved brushing surfaces for5 minutes and the air was sampled for 30 minutes.

A6.7. Site G

Pipe lagging was removed from a boiler room. The enclosure was about 30 m3 and covered about a1/3 of the total area of the boiler room. The 3 stage air lock was located at the entrance to the boilerroom and inside the enclosure a single flap allowed access to boilers outside the enclosure. This 3stage air lock was constructed as separate plastic covered boxes.

Wipe Test:- Wipe test on the floor, produced a visible mark in 10 cm.

Torch Test:- Visible contamination was only apparent on the plastic surface of the enclosure.


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Vacuum Samples:- A sample from the floor gave a result of 12.5 f/mm2 on the filter which equatesto 0.46 f/mm2 on the surface. A sample from the grill gave a result of 18.4 f/mm2 which equates to0.7 f/mm2 on the surface.

Adhesive tape Samples:- Samples taken directly from the surface indicated between 131.6 and53.2 f/mm2 on the floor, between 17.8 and 18.4 f/mm2 on the plastic sheeting walls of theenclosure, 43.3 f/mm2 on the top of the 3 stage air lock inside the enclosure and

Disturbance Test:- The air mover was sealed and the analyst disturbed the area for 5 minutes bywiping surfaces at eye level with a cloth. The HSL clearance involved brushing surfaces for 15minutes and the air was sampled for 17 minutes. The contractors entered to remove the sheetingvery quickly.

A6.8. Site H

Amosite and chrysotile lagging was removed from pipe of an old decommissioned boiler in thebasement of a factory. Three separate layers of plastic sheeting were taped across the stairs leadingto the basement to form a rudimentary 3 stage air lock No plastic sheeting was present either toprotect the floor from further contamination or other items and equipment in the cellar. This sitefailed the visual assessment as asbestos was visibly present on the pipe and in debris on the floor. Asmajor work was required to clean the area the contractors were asked go into the enclosure again.A sample of debris remaining on the pipe showed the presence of amosite asbestos. The analystdemonstrated the technique he would have used to disturb the air. This involved waving a tray upand down vigorously.

A6.9. Site I

Decontamination and encapsulation work was carried out in a large area used for storing lockers onthe second floor of an office block. Some lagging containing chrysotile is thought to have beenremoved. The room itself was used as the enclosure and was approximately 1080 m3 in volume.Two 3 stage air locks existed and were positioned in door giving access to the room at either end.One of these 3 stage air lockers had attached to it a decontamination unit. Most of the windows inthe room were sealed with brown adhesive tape. The windows themselves were not covered with abarrier and the building was on the 4th floor. Also the radiators were not covered and werefunctioning. This made the work extremely hot and uncomfortable. The air extract pipes from the 2air extraction units in the room were placed through open windows taped up with brown adhesivetape. The two analysts carried out a through visual examination of the areas where the asbestos waslocated.

Wipe Test:- Wipe test on the plastic type tiled floor, the metal air mover top surface, woodenwindow sill and metal central heating pipe produced a visible mark in 10 cm. Again, moping andvacuuming were used at this site.

Torch Test:- The floor was visibly dirt without the need to use a torch.


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Vacuum Samples:- Three samples from the floor gave results of 4.94, 4.14 and 1.91 f/mm2 on thefilter which equates to a concentration on the floor surface of 0.19, 0.16 and 0.07 f/mm2.

Adhesive tape Samples:- Five samples were taken from the floor. These gave results of 46.9, 2.2115.3, 29.6 and 123.6 f/mm2 and shows that the distribution of asbestos contamination on the floorsurface was uneven. A sample taken from one of the central heating pipes gave a results of 37.7f/mm2 and two samples from the window sills in the centre of the enclosure gave results of 43.3 and15.6 f/mm2.

Disturbance Test:- The two air movers were sealed and two analysts disturbed the area for 5minutes by hitting surfaces with sealed plastic bags full of air. The HSL clearance involved brushingsurfaces for 5 minutes and the air was sampled for 30 minutes. About 40 % of the area wasdisturbed with the hand brush and a broom would have been more effective with this size of area.

A6.10. Site J

Ceiling tiles containing amosite and chrysotile were removed from an enclosure approximately 300m3. The enclosure included separate 3 rooms, a small cupboard area, and a corridor. A single airextraction unit was located and one end of the corridor and the entrance to the enclosure at theother. The corridor stretched for about 10 m past the rooms where the asbestos was removed andone of the analyst’s pumps was placed near the air mover unit. Unusually, a large proportion of thefloor was protected with plastic, however, this was solely to protect a carpet underneath and theplastic was cut to cover only the area of the carpet. The analyst carried out a thorough examinationof the areas where the asbestos was removed and some areas on the floor and cupboard space.Other doors entering into the enclosure area were sealed with tape. Some MMMF insulationremained in place during the air test.

Wipe Test:- Wipe test on the plastic covered floor , window sill produced a visible mark in 10 cm.However a draining board next to a sink in one of the rooms did not produce a mark on the filterpaper. This smooth surface is very easy to wipe and clean down.

Torch Test:- Two different HSL personnel performed this test and the results are listed below:

YesYesSwitchesNoNoRadiator

YesDifficult toassess

FloorYesYesShelvesNoYesWindow sill

HSL 2HSL 1Location

The results are not consistent, possibly as operator 1 had less experience than operator 2. Operator1 reported that lighting problems made some areas difficult to see. The shelves had small pieces of debris on them that were later found to contain amosite.


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Vacuum Samples:- Samples from the three rooms gave results of 66.57, 3,53 and 29.47 f/mm2 onthe filters. These figures are equivalent to a surface concentration on the floor of 2.53, 0.13 and 1.12f/mm2. A sample taken from one of the shelves in the cupboard area gave a results of 13.63 f/mm2on the filter which is equivalent to and concentration on the shelf of 0.56 f/mm2.

Adhesive tape Samples:- Duplicate samples within 50 cm of each other were taken in from thefloor space in each of the room and corridor. The results for all the adhesive tape samples are listedbelow:-

5.4ShelfCupboard42.5FloorCupboard

10.822.8FloorCorridor107108.1FloorRoom 3

7.6Bench near sink85.5178.4FloorRoom 232.864FloorRoom 1

Result 2 f/mm2

Result 1 f/mm2

LocationArea

The floor area is the area with the most contamination of ‘free’ asbestos fibres.

Filter swab samples:- The results listed in the table below are counts obtained from air filterswhen pressed directly against, applying as even a pressure as possible, suspected contaminatedsurfaces. Again, duplicate samples, within 50 cm, were obtained of the floor area.

2.9ShelfCupboard7.613.7FloorCorridor5080.6FloorRoom 3

2.3Bench near sink28.512FloorRoom 26.522.2FloorRoom 1

Result 2 f/mm2

Result 1 f/mm2

LocationArea

These results appear more variable and in almost all cases are lower than those taken with theadhesive tape.

Disturbance Test:- The air mover was sealed and the analysts disturbed the area for 5 minutes byhitting surfaces with a sealed plastic sack full of air. The HSL clearance involved brushing surfacesfor 5 minutes in each room and the air was sampled for 30 minutes.

A6.11. Site K

This operation involved the removal of an asbestos board (AIB) attached to a door to a riser in asports building. The volume of this enclosure was approximately 10m3 however the added area of


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the riser increased the volume by about 200 . The door was on the first floor of the building. Theworkers had enclosed a small store room without removing its contents. An air mover was placed inits centre and nearly filled the whole area. Neither the floor or any of the contents remaining in theroom were protected from possible contamination. The workers had removed the whole door withthe asbestos board attached, wrapped the whole object in plastic and planned to dispose of thiswithout separating the board from the door. This remained in the room during the whole clearanceprocess. The exact nature of this removal operation was not known until the author arrived at thesite and its suspected that it is not a typical type of work. On a visual inspection it became apparentthat the workers had previously removed the door from the floor below and that this had effectivelycompromised the integrity of the enclosure since any asbestos debris or fibres falling would haveentered the room on the floor below. The analyst examined the area of the door and found somedebris still attached to the door frame. Having seen that the enclosure was compromised the analyststated that he would not do a clearance assessment. The air test was performed on the basis that theanalyst was performing a reassurance test.

Wipe Test:- Wipe test on the floor, and on the shelf produced a visible mark in 10 cm. Howeverthis could have been due to dust deposited before the removal operation.

Torch Test:- Areas examined by the torch are listed in the table below:

NoYellow painted metalAir moverYesPlastic Air lockDifficult to assessConcreteAir riserYes (Grains of material)Grey metalShelfYesTilesFloor DirtyType of Surface Location

These results suggest that either a vacuum cleaner is not the most efficient way of cleaning a surfaceor that the workers did not make any serious attempt to clean the area.

Vacuum Samples:- Results from the vacuum samples are listed below:

0.4611.98Grey metalShelf

0.4211.14Smooth tilesSecondStep

0.174.46Smooth grey tilesFloor

Concentration on surfacefibres / mm2

Concentration on filterfibres / mm2

Type of Surface Location

Surface Samples:- Results for the samples taken with the adhesive tape are listed below:

2.9Smooth grey tilesFloor 26.7Smooth grey tilesFloor 1




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3.2Plastic3 stage airlock floor

2.5Grey metalShelf5.4Smooth tiles1st Step

Filter swabs:- Filter swab samples were also taken at this site, from similar locations as theadhesive tape samples and the results are listed below.

11.4Plastic3 stage airlock floor

0.6Grey metalShelf0.3Smooth tiles1st Step2.2Smooth grey tilesFloor 1



Disturbance Test:- The air mover was sealed and the analysts disturbed the area for 5 minutes bybrushing surfaces with a square piece of cardboard. The HSL clearance involved brushing surfacesfor 5 minutes and the air was sampled for 30 minutes.

A6.12. Site L

Sprayed asbestos was removed from 3 concrete columns inside a first floor room of a corner shop,being converted into a hairdressers. The enclosure covered only part of the first floor room and wasapproximately 30.6 m3. This is only a very rough estimation of the volume since the enclosure wasoval in shape. Unusually, most of the area of the floor, except for the wooden window sills and theimmediate area around the columns was covered by blue plastic. However, areas of the floor plasticwere visibly wet. The analyst conducted a very brief visual assessment. The columns appearedvisually clear of asbestos.

Wipe test:- Although visibly clean, both the plastic floor covering and the enclosure walls produceda visible mark in 10 cm.

Torch test:- It was difficult to determine from the blue glare of the plastic if the material was dirty. Itwas also difficult to differentiate parts of the exposed wooden floor planks from any dirt.

Vacuum samples:- Two vacuum samples were taken of the plastic floor covering. The first was inan area identified as sampling area A and was in the centre of the enclosure the second was in areaC and was nearer the entrance to the 3 stage air lock attached to the enclosure. These two samplesgave results of 17.04 and 56.27 f/ mm2 on the filter which is equivalent to a surface concentration of0.65 and 2.14 f/mm2.

Surface samples :- Results for the surface sample techniques are compared in the table below. Alldifferent sample groups were taken within very close proximity from each other. Three samplegroups were taken from the plastic sheeting on the floor. Those designated as area A were taken in


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the centre of the enclosure, those designated as Area B were taken close to one of the columns andthose designated as area C were taken in a location closer to the 3 stage air lock.

544.4238.164.3Varnished woodWindow Sill81.88015.3Plastic floor3 stage air lock143.984.741.2PlasticFloor Area C475.3223.85.4WoodFloor Area B85.2124.38.3Plastic Floor Area A

Forensic tapeAdhesive tapeFilter swabsSurface Concentration (f/mm2)Surface TypeLocation

Disturbance Test:- The analysts disturbed the area for 5 minutes by wiping surfaces at eye levelwith a cloth. However the air mover was unsealed during this time. Despite the presence of waterinside the enclosure it failed the clearance air monitoring. The two results obtained by HSL indicatethat the concentration of asbestos fibres in air was between 0.06 ad 0.07 fibre / ml. The HSLclearance involved brushing surfaces for 5 minutes and the air was sampled for 16 minutes giving aresult of 0.18 fibres /ml. The air mover was switched on for a hour and the area was re-disturbed bythe analyst. The author was not present to view the second 5 minutes disturbance by the analysthowever a pump placed inside the enclosure just afterwards recorded a result of < 0.01 fibres/mlconfirming the analyst’s clearance results. After the area was declared clear a vigorous disturbancewith a hand brush was performed for 5 minutes and the air sampled for 60 minutes. The twosamples gave values 0.13 and 0.14 fibres/ml. Return visit

The area was revisited the next day after the workers had removed the enclosure. After 4 minsdisturbance with a brush and 60 minutes sampling results of 0.04, 0.08 and 0.03 fibres / ml wererecorded from 3 pumps placed in the room. The room was very dusty and the filters heavily loaded.This may have resulted in an under count of the ‘true ‘ concentration of fibres collected. Twoadhesive tape samples were obtained, one from the wood around the pillar and the other from theconcrete pillar. These samples were counted and results of 75.5 fibres were found on the adhesivetape from the floor and 47.7 fibre / mm2 on the pillar. Again this demonstrates that the area wascontaminated despite being protected with plastic and that the area which is not disturbed by theanalyst (the floor ) has the highest concentrations of free fibres.

A6.13. Site M

Asbestos AIB boards were removed from the ceiling of an old boiler room in a basement. The wallswere covered with plastic and the floor covered with hard board. I was informed that the floor wascovered with plastic and the hard board placed on top. Gaps between the hard board were sealedwith tape. The room was separated into one major and one minor compartment and wasapproximately 54 m3. This is only a rough estimation as the enclosure was not shaped in a uniformmanner. Pools of almost dry PVA remained on the floor through out the assessment. Small pieces ofdebris were visible but further analysis found these to contain vegetable fibres. This was the only sitewhere the firm contracted to remove the asbestos was a subsidiary of a company dedicated tocleaning services.


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Wipe tests:- The following wipe tests were performed:-

Only a faint mark visiblePlastic walls of enclosureOnly a faint mark visible Floor - Tape between hard boardOnly a faint mark visibleFloor - Tape between hard boardMark in 10 cm wipeTest Area

The wipe sample did not work on the hard board as the friction between the two materialsdeteriorated the structure of the Whatman filters.

Torch test:- It was very difficult to apply the torch test to the brown coloured hard board. Althoughthe light, shone at an acute angle to the floor, did pick out some specks of debris these were laterfound to contain vegetable fibres.

Vacuum samples:- Two vacuum samples were taken of the hard board floor. These producedresults of 2.27 and 1.23 f/mm2 on the filter which is equivalent to a surface concentration of 0.086and 0.047 f/mm2 on the floor surface.

Surface samples:- Results from the 3 other surface sampling techniques tested are shown in thetable below. Again the particular group of samples were tested within close proximity of each other.The adhesive tape samples were sampled on the plastic tape between the board to avoid collectingthe paper like hard board surface. The forensic tape samples were sampled directly on the hardboard without any difficulty. The sample labeled AC was taken in the smaller area and the sampleslabeled RC were taken in the main area.

8.1Plastic floor3 stage air lock1.612.31.9Floor RC 25.1752.9FloorRC 18.312.79.9FloorAC 1

Forensic tapeAdhesive tapeFilter swabsSurface Concentration (f/mm2)Surface TypeLocation

Disturbance Air Tests:- The air mover was sealed and the analysts disturbed the area for 5 minutesby hitting surfaces with an inflated plastic sack. The HSL clearance involved brushing surfaces for 5minutes and the air was sampled for 30 minutes.

A6.14. Site N

A6.14.1.First Enclosure

This enclosure involved the removal of sprayed asbestos from around metal beams placed on pillars supporting the ceiling. The enclosure was built on metal poles and had a wooden floor covered withcard board and sealed together with tape. It was a very large enclosure with a low ceiling andbeams and poles, supporting the floor, restricted the movement space. The enclosure was ‘L’shaped, about 10 m wide at one end, 50 - 60 m long and about 20 m long at the other end, and lessthan 2.5 m high in most places. Without the equipment or time for accurate measurement I estimated


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the volume to be between 1870 m3 and 1562 m3 . One of the pillars spread along a wall that spreadalong the whole length of the enclosure. At one point there was a space between the bricks of thewall and the metal beam (about 4m long and the height of a brick). Another smaller enclosure couldbe seen on the other side but this enclosure was not assessed during this visit.

Wipe tests:- Wipes on the metal grids only showed the colour of the rust from the metal. A singlewipe from the floor area showed a dark line in 10 cm.

Torch test:- Speckles of debris could be seen on the floor and on the cables held in trays attachedto the ceiling. All torch tests showed speckles of white debris.

Vacuum samples:- Not taken at this site

Surface samples:- - Results from the 3 other surface sampling techniques tested are shown in thetable below. Again the particular group of samples were tested within close proximity of each other.

155.5Plastic coverLight Cable 2118.724.912.7 Floor

8580.66.7Plastic coverLight Cable 118.18.55.1Metal girder C 144.7612.7Floor boardB

811.21.6Metal girderA Forensic tapeAdhesive tapeFilter swabs

Surface Concentration (f/mm2)Surface TypeLocation

Disturbance Air Tests:- The two air movers placed at one end of the enclosure nearest the air lockwere sealed and the analysts disturbed the area for 5 minutes by hitting surfaces with an inflatedplastic sack or waving it about in the air. The area failed the initial clearance air monitoring. The 7pumps used by HSL during the analysts disturbance assessment recorded one value of 0.13 anotherof 0.04 and the rest were all 0.01 fibres / ml. A comparative brush test was performed where thefloor area and girders were brushed for 20 minutes. This test found that 4 out of 6 results recordedresults higher than 0.1 fibres / ml. The highest was 0.23 and the lowest was 0.05 fibres / ml and themedian result was 0.11 fibres / ml. Many of these filters were heavily loaded with debris makingthem difficult to count and the HSL analyst may have under estimated the ‘true’ number of fibres onthe filter. One pump was withdrawn because of a failure.

A6.14.2.Examination of area after 1st enclosure was removed

The area under the 1st enclosure was examined after the workers had removed the plastic sheetingand scaffold. Fibrous debris containing amosite and chrysotile asbestos was found on a woodenpallet propped up against the wall and on the concrete floor. The concrete floor was visibly dirty.The foreman stated to me that it was possible that the asbestos debris was present before theremoval operation. Workers were seen cleaning this area on subsequent visits. Surface sampleswere taken on several locations underneath the area were the enclosure had been and the results areshown in the table below:


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6.71.30.6ConcreteC1A Floor underbeam

1.52.24.1Concrete CE ½ FloorForensic tapeAdhesive tapeFilter swabs


A vacuum sample from the concrete floor gave a result on the filter of 5.7 fibres/mm2 which isequivalent to a surface concentration of 0.22 f/mm2. All the results suggest a low level of ‘free’fibres on the surface. However, it is possible that the dirtiness of the floor affected the efficiency ofthe surface sampling techniques.

A6.14.3.2nd Enclosure area

This second area was just as large as the first and was approximately 324 m2. In some parts the roofwas less than 2.5m high and in others more than 4 m. The volume was estimated to be between 810and 924 m3. The enclosure walls were double sheeted and the floor consisted of planks coveredwith a thick cardboard or hard board like material. The cardboard sections were sealed togetherwith tape. There was a small tear in on of the sections of cardboard and the concrete floor, about 5m below, was visible. Metal poles from the scaffold supporting the floor protruded through the cardboard. The open ends of these poles were taped over but this tape had been removed or split onsome of them. A large number of boards in the centre of the enclosure were damp, possibly fromthe spraying of PVA, and had swollen. This enclosure didi not pass the visual assessment. Debriscontaining amosite and chrysotile asbestos were found in the duct carrying electric cable along theceiling and small pieces of debris were seen on the floor. An unsealed air vent was found in theenclosure and a smoke test indicated a flow of air into the enclosure when the air extraction fanswere working. This enclosure failed the analyst’s visual assessment several times before an air test.

Torch test:- Small specks of debris were visible on the floor area when the torch was shone at anacute angle.

Vacuum samples:- Two vacuum samples were taken from the floor, the first in a location identifiedas RC 1, 4 m from the enclosure entrance and the second at a location identified as RC 2, on thefloor relatively close to a bare metal supporting beam. These samples recorded a concentration of 11.37 and 104.14 f/mm2 on the filter which are equivalent to a concentration on the surface of 0.44and 4 f/mm2.

Surface Samples:- Results from the surface samples are shown in the table below. All groups ofsamples were taken in close proximity to each other. The adhesive tape samples from the floor weretaken on the surface of the tape holding the boards together rather than the card board surface.

42.417.1PlasticOV Grill on air vent126.8118.110.8Floor RC 2 (on floor near beam)91.17.5Floor RC 1 (4m from enclosure entrance)

Forensic tapeAdhesivetape

Filter swabsSurface Concentration (f/mm2)Surface TypeLocation


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The results in the table below are from a return visit after the cleaning operation was completed. It isknown the floor was vacuumed with a H type cleaner. Samples labeled RC 3 were taken in almostthe same area as those labeled RC 1 in the previous table.

61.5PlasticFloor of 3 stage air lock44.68.611.5Metal BeamM1147.3112.87Floor RC 4 (on floor near beam)195.340.178.3Floor RC 3 (5m from enclosure entrance)



The vacuum cleaning in this case has not made an impact on the surface concentration of fibres onthe floor.

Vacuum samples taken in locations RC 3 and RC 4 gave results of 53.59 and 30.48 f/mm2 on thefilter which equate to a surface concentration of 2.03 and 1.15 f/mm2.

Disturbance Air Tests:- The four air movers placed at one end of the enclosure were sealed andthe analysts was observed, through the plastic walls of the enclosure, disturbing the area for about 5minutes by hitting surfaces with an inflated plastic sack or waving it about in the air. The HSLclearance involved brushing surfaces for 15 minutes and the air was sampled for 30 minutes.

A6.15. Site O

This site also involved the removal of sprayed asbestos from structural metal beams. It was a verylarge enclosure of about 8 m high. I estimated the area to be between 800 and 1080 m2 and thevolume to be between 6000 and 8640 m3. The ceiling or one of the pipes was leaking and there wasa large puddle of water near the centre of the enclosure. The floor surface was road quality tarmacand the analyst examined this, marking off areas to be cleaned with brushes and vacuum cleanerswith chalk. I was informed that the floor had been protected with two layers of plastic and this hadbeen removed prior to the clearance test. A wet injection technique had been used on the materialbut the fluid from this had leaked under the sheeting.

Wipe testing:- It was found impractical to perform the wipe test on the rough tarmac surface.

Torch test:- A fine sludge was settling in some of the small pools of water and the edge of theplastic appeared dirty in places.

Vacuum samples:- The following vacuum samples were taken:

Surface Concentration(Fibres/mm2)

Concentration on filter(Fibres/mm2)

Surface TypeLocation


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0.256.82PlasticTop of Banister2.0152.91TarmacTop of scaffold14.8389.73TarmacFloor (Centre)

Surface sample:- The table below shows the results from the 3 surface techniques tested.

155.7RubberPlatform 2285.49.2RubberPlatform 184.965.3PlasticBanister1348422.8TarmacFloor Edge After Scrubbing

1,021.89.80.6Tarmac Floor (Centre)



Disturbance Air Tests:- The two air movers placed at one end of the enclosure were sealed andthe analysts disturbed the area for about 5 minutes by hitting the walls of the enclosure with anplastic sack in which he had placed a roll of tape. Once the air was declared cleared a comparativebrush test was performed and the floor area was brushed for 15 minutes and the air sampled for 30minutes. Of the seven samples taken six results 0.06 fibres/ml or over. The maximum was 0.09fibres and the minimum 0.02 fibres/ml. The median value was 0.06 fibres / ml. This area failedHSL’s clearance air monitoring.

A6.15.1.2nd Enclosure

This area was in a similar location and almost as large as the first. About a 1/5 of the enclosure wasdamp with pools of water present.

Wipe test:- Not practical to perform on a tarmac surface.

Torch test:- Silt was settling in the pools of water and the edges of the plastic walls of the enclosurewere visibly dirty in places.

Vacuum test:- A single sample from the tarmac floor gave a result of

Surface tests:- Only the forensic tape samples were used as, from the results on the first test, thesewere more efficient on a tarmac surface.

1,021.8TarmacFloor (Top Left) S8Too much debris to countTarmacFloor (Bottom Right) S3

185TarmacFloor (Centre Right) S2375.1Tarmac Floor (Top right ) S1

Forensic tapeSurface Concentration (f/mm2)Surface TypeLocation


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216.1ConcretePillar (Not flat surface)566.4Plastic Enclosure wall (flat surface)377.1Plastic Plastic cover (Doctors couch)

417.2RubberScaffold 213.1ConcretePillar base S4483.1TarmacFloor (Centre) S9

1,403.7TarmacFloor (Centre Left) S7

Results show that the right hand side of the enclosure area is the most heavily contaminated. Thelowest results was obtained from a pillar and emphasises the importance of disturbing flat surfacessuch as the floor rather than the walls or ceiling from where the asbestos was removed.

Disturbance Air Tests:- The two air movers placed at one end of the enclosure were sealed andthe analysts disturbed the area for about 5 minutes by hitting the walls of the enclosure with anplastic sack in which he had placed a roll of tape. Once the air was declared cleared a comparativebrush test was performed. The floor area was brushed with a broom for 15 minutes and the airsampled for 30 minutes. Results from the 6 pumps in the enclosure ranged from 0.18 to 0.23fibres/ml, well above the clearance indicator, despite the amount of water present.

Site P (Post removal investigation)

A visit was made to a school where asbestos panels and boards were removed from a room. Therewere two floors and stairs led from the first floor to the second and would have probably beenincluded in the enclosed area. The visit took place on the day following the asbestos clearanceassessment. The area would have had a volume of approximately 450 m3.

Visual assessment:- A large number of boards had been thrown into a room. They appeared to beof glass fibre. Fragments of debris were found on the floor and attached to nails still in the woodenframe. The fragments of debris were found to contain chrysotile asbestos and the debris of the floorcontained amosite asbestos. All areas appeared to show dirt and a torch or wipe test would haveproduced a positive result.

Surface sampling:- The following results from the surface tests were recorded.

14.5Floor 2 (Area A)1.90.91.3Varnished wood Floor (Area C)

10.5150Floor (Area B)0.636.10Vinyl Tile Floor (Area A)




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Results indicate that apart from a the scattered pieces of debris containing asbestos very few ‘free’fibres had contaminated the floor. A possible scenario for this is that the floor area was probablyprotected in some way and the debris ‘fell’ onto the floor area when the sheeting was removed asthe majority of the free fibres may have remained in contact with the sheeting by their electrostaticattraction.

USE OF WIPE TESTS IN INCIDENTS

During this project there were a number of occasions where HSL has been asked to support FODenforcement action and access the level and extent of asbestos contamination. Tape samples haveproved to be a very useful tool in these investigations and are described in the two section below.

Site Q

A room in a city council house had been partitioned into two. A cabling for the computers had beenrerouted through a service duct in a false ceiling above a corridor. Access to the service duct wasobtained by drilling through an asbestos wall panel. Dust from the drilling had been discovered onthe floor and the area was suspected to be contaminated. Samples of dust were collected from thedrilling on the wall panel, behind the door and the dust bag of a vacuum cleaner. Filter and adhesivetape samples were taken of the same areas and the results are compared below:-

5.72.9 Vacuum cleaner393.11,189.3WoodDoor frame

Too dense to count1,279.6Not knownFloor behind doorAdhesive tapeFilter swabs


Both the tape and filter swabs around the door area had a high density of free asbestos fibres. Theadhesive tape samples had many larger asbestos fibres on them than the filter samples.

Site R

An area in a hospital had under gone an asbestos removal operation and had been given aclearance. The polythene sheet had been retained in place for the benefit of painters. Adhesive tapesamples were used by HSL to determine the spread of the contamination. The adhesive tape can beremoved by plasma ashing and the fibres positively identified using polarised light microscopy. Aportion of the tape is placed on a glass slide and plasma ashed for about 4 - 7 hours. Theappropriate refractive index liquid is then placed on top of the debris and a cover slip placed on topof the liquid. The fibre is then identified by its dispersion colours under phase contrast conditions.The results from the adhesive tape samples are listed below:-

Concentration of fibresIdentificationLocationHEALTH AND SAFETY LABORATORYAn agency of the Health and Safety Executive

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5.1Asbestiform fibre presentTape sample of polythene outsideroom in corridor

107.5Amosite asbestos presentTape sample from polytheylene abovesink

1.6Asbestiform fibres Tape sample from polythene sheet inroom

Amosite asbestos presentTape sample of partition wallon surface (Fibres/mm2)

The adhesive tape samples showed heavy asbestos contamination and taken from the polythenesheets covering the sinks and furniture inside the room where the asbestos removal operation hadtaken place and samples taken of the polythene sheeting on the floor outside the room showed verylittle surface contamination.


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Documents

Improved Methods for Clearance Testing and Visual ... · 5. To prepare a draft MDHS on clearance sampling and testing and publish results. Main Findings 1. Laboratory investigations