VOLUME 71 • NUMBER 4 • OCTOBER/DECEMBER 2018 · 2019. 2. 18. · 12 Delta Road Blairgowrie Randburg PO Box 72366 Parkview 2122 Tel: +27 11 886-5985 Fax: +27 11 886-1332 Cell No:

VOLUME 71 • NUMBER 4 • OCTOBER/DECEMBER 2018

Published quarterly by the Mine Ventilation Society of South AfricaCSIR Property Cnr Rustenburg and Carlow RoadEmmarentiaP O Box 291521 Melville 2109Tel: +27 11 482-7957 Fax: +27 11 482-7959 / 086 6607171E-mail: [email protected]

[email protected]: http://www.mvssa.co.za

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Material in this publication may not bereproduced in any form whatsoever withoutwritten permission from the Editor.

Copyright © 2018 of the Mine VentilationSociety of South Africa

Contents

Cover Picture:

Journal of theMine Ventilation Society

of South Africa

Editorial: Who needs cooling? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

From the desk of the President - Year-end message . . . . . . . . . . . . . . . . .4

Developing a protocol to evaluate continuous miner heading ventilation systems using practical on-site measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

The Sibanye Gold Noise and Dust Management Strategy to achieve the revised MHSC Milestones issued to the mining industry on 19 November 2014 . . . . . . . . . . . . . . . . . . . . . . . . .11

Electricity savings in automated mines . . . . . . . . . . . . . . . . . . . . . . . . .16

In-Stope dust control at Beatrix Gold Mine . . . . . . . . . . . . . . . . . . . . .22

Prestigious recognition of MVSSA members . . . . . . . . . . . . . . . . . . . . .28

Outside Front Cover Picture: Photographer - Miguel Coelho. MVSSA PhotoCompetition Runner-up 2018. The photo shows the main fan station in theforeground and a headgear of a shaft that was constructed in the 1920s.

Journal of the Mine Ventilation Society of South Africa, October/December 2018 1

It has been a very hot start to Spring in thispart of the World. Judging by the long hot2018 Summer in the Northern Hemisphere, weare probably heading for a series of hot spellsand violent storms associated with them.Cooling of domestic, office, commercial environments is therefore increasingly popularto provide not only "comfortable" conditionsbut also to generate settings that are conduciveto safe and cogitative work.

This editorial was inspired by personal reflections of the levels of knowledge requiredfor students attempting Paper 2 (ThermalEngineering) in the Certificate in MineEnvironmental Control. The syllabus forThermal Engineering is unique in terms of itscontent matter and the level of proficiencyrequired for the detailed analysis of minerefrigeration and cooling plant performance.This is aimed, primarily to generating conditions conducive to safe and productivework while extracting the highest efficiencyfrom these energy-extensive systems.Ventilation engineers in deep level mining havemastered this science for at least the last fiftyyears during which the operation of deep andultra-deep gold mines constituted the backboneof this Industry and of this Country's economy– good or bad as these may be judged bytoday's critics.

The question has dawned whether today'sSouth African Mining operations still need andapply that specialised knowledge and thosespecialist analytical skills – in house. After all,not many mines operate refrigeration plants,many of those that did in the past have nowshut down, others, still in operation, have"retired" their refrigeration plants to cut production costs. Thirty years ago, any goldmine operator would budget for the operationof several such plants many of them withmulti-stage compressors (yes, what are they?),several of them located underground, withtheir associated, numerous operational issues,all linked to complex chilled water networksthat included a variety of energy recovery technologies – yes, some twenty years beforeEskom invented load shedding! And then cameice generation technology age...

Typically, ventilation engineers of the day were

Marco BiffiPr. Eng.

Honorary FellowHonorary Editor

Please send your comments and

opinions to [email protected]

required to use that requisite knowledge andexperience to assess the effectiveness and efficiency of those costly systems. Given today'sstate of affair does it make sense to have a specialist on the payroll who is able to calculatethe mass-flow of ammonia in an evaporator toachieve 7.5MW of cooling effect or to performan analysis of the plant's performance usingThorp and Bailey-McEwan? The "modern" wayof doing things is to bring in a consultant or anequipment manufacturer that will "deliver thegoods" and move-on. It's not important if thesystem is inefficient, "so long as it producescold water" and if it breaks, "we will get inanother lot to fix it". Of course, the situation isnot necessarily that bad, but somehow, we, theengineering profession across the spectrumseem to have lost "the art and science" of engineering. Today, more than ever, the driversare production and the costs associated therewith. Working conditions need to meetbare minimum levels of acceptability and ifthese are not legislated or enforceable thenthey are not a priority to be considered.

This somewhat cynical opinion has developedfrom observations of several, serious as well as"ordinary" incidents over several years thathighlight the helplessness of the situation inwhich the mine ventilation profession findsitself. Perhaps, more alarmingly, it is symbolicof the misunderstanding and misconceptionsthat our principals seem to hold in relation tothe value of this profession in modern mining,particularly in enabling the achievement ofzero harm.

Irrespective of these issues, the profession isfacing uncertain times starting from the questfor that "formula" necessary to revitalise itsvalue within the Industry. At the base of thismust be the dedication of individuals backed bya thorough knowledge of the subject matter, inall its complexities, and in its ability to adapt tomeet the challenges that this ailing Industry iscurrently experiencing. These are considerable for the new generation ofVentilation Engineers entering the ranks – thosewho still must pass Paper 2.

As we reach the end of this year, a time manybelieve to represent a period and opportunityfor renewal, let us pause, take a deep breath

Who needs cooling?

Editor’s Comment

2 Journal of the Mine Ventilation Society of South Africa, October/December 2018

THE MINE VENTILATION SOCIETYOF SOUTH AFRICA OFFICE BEARERS

President:Mr Marthinus van der Bank

Senior Vice President:Mr Ronald Motlhamme

Junior Vice President:Miss Julize van Niekerk

Honorary Editor:Mr Marco Biffi

Honorary Treasurer:Mr Wynand Marx

Honorary Chairman of Education:Mr Morné Beukes

Immediate Past President:Mr Kobus Dekker

COUNCIL MEMBERSMr Frans Cloete, Mr Frans Gume, Mr Johan Maass,Mr RH McIntyre, Mr Barry Nel, Mrs CeciliaPretorius, Mrs Glenda van der Westhuizen

PAST PRESIDENTSMr Bruce Doyle, Mr Len de Villiers,Prof Jan du Plessis, Mr James J van Rensburg,Mr Dries Labuschagne, Mr Henry Moorcroft,Mr Vijay Nundlall, Mr Andrew Thomson,Mr Frank Von Glehn

BRANCH REPRESENTATIVESThe Collieries Branch

Mr Neil McPhersonThe Free State Branch

Mr Johan Pienaar The Northern Branch

Mr Sydney MitchellThe Western Branch

Mrs Louise Kleynhans The Eastern Branch

Mr Paul BothaThe International Branch

Mr Frank von Glehn

EDITORIAL COMMITTEE MEMBERSMr Marco Biffi (Hon. Editor), Mr Bruce Doyle,Mr Frank von Glehn, Mrs Cecelia Pretorius,Mrs Debbie Myer

MVS Public Relations Committee - Communication Facility

The MVS Public Relations Committee would appreciate any feedback on any matter relating to the operation of this society. This facility has been initiated inorder to ensure that any matter that is raised is given due attention.

It would be appreciated that the questionnaire below be completed and faxedor e-mailed to any one of the person/s listed below:·• Marco Biffi on [email protected], or• MVS Office, Fax 086 660 7171, e-mail [email protected]

All communications will remain confidential in terms of identification of the communicator. You are welcome to remain anomymous.

Name:

Telephone number:

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E-mail address:

Nature of communication (please mark with an X)

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Details of communication:

SECRETARIAL

CSIR Property, Cnr Rustenburg and Carlow Road, EmmarentiaP O Box 291521 Melville 2109Tel: +27 11 482-7957 Fax: +27 11 482-7959 / 086 660 7171E-mail: [email protected]

[email protected]: http://www.mvssa.co.za

Secretary:Madelein Terre’Blanche

Assistant Secretary: Liezl Slabber


and rekindle those good intentions with a dash of ingenuity and enthusiasm. Let us hope for a serene and calm period that will enable usto stop, reflect and recharge – without the stress and anxiety associatedwith extreme weather conditions, uncertain times, crime, poverty...

May this be for you all, a peaceful, serene and joyous time. Best Wishes.

Footnote: In using the title of this editorial, I acknowledge but also apologise to Jimmy Page and Led Zeppelin as a whole.

Year-end message

From the desk of the President

As we reflect on another year that hasflown by with amazing speed we generally tend to dwell on our achievements and also on areas wherewe did not do so well both in our personal and professional lives.

The Mine Ventilation Society of SouthAfrica (MVSSA) has been involved,through its members, in variousendeavours to improve Health andSafety in the mining industry.

Regrettably, the year has been marredby a series of fatalities in the SouthAfrican Mining Industry, several ofthem as the result of disasters on ascale not seen in many years. Weremember the loss of our colleagues inthe hope that the lessons learned fromtheir sacrifices will ultimately bringabout a marked and profound improvement in the Health and Safetyof South African mining operations.

Also, in 2018, we experienced the passing of colleagues, who lost theirlives on the roads and through illness.The wellbeing of their families andloved ones remains in our prayers especially during this festive season.

Once again this year words such as"Downscaling, Voluntary Separation,Closure, Right-Sizing, etc." were part ofnearly every conversation on the SouthAfrican Mining Industry north of CapeTown. However, it is heart-warming tonotice and experience the unrelenting

resilience and positive attitude of ourmembers and our Industry Partners.

During my presidential address I poseda number of challenges to the currentMVSSA Council and Executive. It iswith pride that we can reflect on a few,and important milestones have alreadybeen achieved:

• After a very successful and well-attended national conference held inMay, planning of the 2019 nationalconference is already on the way;

• The structuring of our new qualifications is also well on track.

- The pilot course for the new NQF-3 Qualification (Mine Ventilation Observer) is scheduled to commence during first half of 2019;

- The new NQF 4 Qualification (Mine Ventilation Officer) is scheduled for 2020;

- The new NQF-6 Qualification (through Wits University) will also commence during 2019.

- The new NQF-7 Qualification (through the Quality Council for Trades and Occupations [QCTO]) has been gazetted.

Almost all new qualifications are therefore registered and the challengenow is to provide the input and supportnecessary to pilot and implement thesefully – a task on which many of us willbe required to support.

• Electronic circulation of the journalhas been piloted. A lot of praise hasbeen received so far from memberswho participated in the pilot.

• The Presidential roadshows to thebranches held so far were successfuland it was gratifying to see thesociety growing constructively andenthusiastically.

• The uplifting of our identity throughthe broader society branding is yet

another, real highlight.

• In August 2018, China Hosted, the11th International Mine VentilationCongress (IMVC) and by all accountsit was a successful event, with morethan 800 delegates registered andvarious papers being presented fromnumerous mining countries world-wide including the USA,Australia, China, India, South Africa,Canada, Germany, England, Japan,Poland, Peru, Tanzania and Chile.

• We as South Africa and specificallythe MVSSA were honoured to deliverone of the five Keynote addressesduring the opening day of the IMVC.

• The introduction of some prestigiousprizes and awards at the PresidentialBanquet was a great success storyand has taken the event to the nextlevel.

• The application for the registration ofthe MVSSA as a Professional Bodywith the South African QualificationAuthority is currently progressing andwill be expedited during the firstquarter of 2019.

The efforts and time devoted by eachand every Council Member, in ensuringpositive growth and progress towardsour strategic goals, is highly commended and their continual commitment is appreciated.

Through many planned activities, theMVSSA continues to demonstrate commitment to our members. Inexchange, the Society requires anequally dedicated involvement from themembers in its activities.

Lastly I want to say to everyone travelling during the festive season doso by driving safely, be aware of othermotorists and return home safely.

May you enjoy a blessed FestiveSeason.

Marthinus van der BankMVSSA President 2018/2019


ABSTRACT

More than 40 individual continuous miner heading ventilation tests have been completed in Anglo ThermalCollieries using practical on-site flow velocity and directionmeasurements to evaluate the ventilation systems beingused. These have been carried out on all coal winning operations of continuous miners and across all types of ventilation system.

The measured ventilation flows allow for the calculation ofscrubber fan recirculation, as well as identifying areas ofexcessive turbulent flow, or of very low flow.

Results have been used to identify acceptable or good conditions, along with unacceptable or poor conditions.

An Anglo Coal ventilation test protocol is being developedfrom the practical aspects of the SIMRAC COL518 protocoland from the individual heading ventilation tests carried outacross Anglo Thermal Coal collieries by from 2004 to 2015.

It has been derived in such a way that it enables senior ventilation officials to carry out the required measurementsand confidently evaluate the results. This allows for relatively quick identification of compliant or non-compliantheading ventilation systems, and to actively manage change.

1. INTRODUCTION

Heading ventilation test measurements have been made forpractical research and development purposes in AngloThermal Coal (ATC) Collieries over several years. The testsincluded all types of heading ventilation in use, typicallyscoop brattices, half brattices, free standing fans, and on-board scrubbers, or combinations of these. The headingsranged in depth from 12 metres to 41 metres, including boxing to the left or right. The continuous miners (CM)operated with and without shuttle cars (SC), and wereequipped with either single or double scrubbers.

Results have been used to identify acceptable or good conditions, along with unacceptable or poor conditions. Inparticular results have shown that scrubber fan recirculationcan exceed the permissible 50 %, and that in some circumstances it is impossible to accurately calculate therecirculation. Results also show that force intake ventilation

definitely improves intake penetration in all headings, however it would seem that that during pillar box cutting,ventilation penetration to the face is often reduced.

The work is concluding with the compilation of an AngloThermal Coal protocol for practical evaluation of a headingventilation system, which must be applied when anychanges or modifications are to be made to a heading ventilation system, or to existing dust scrubber fan and spraysystems installed on the continuous miners. This enablessenior ventilation officials to evaluate and quantify their current and future heading ventilation systems in aconsistent, repeatable and reliable method.

2. OBJECTIVES OF HEADING VENTILATION TESTS

The objectives of the testwork were to practically measureventilation flow directions and quantities in working continuous miner headings, and to use the ventilationmeasurements to determine the best practical operating ventilation systems for continuous miner headings, and toidentify difficult or inadequate ventilation conditions.

Additionally the practical measurements have been used toevaluate and calibrate and confirm the computer calculatedresults for the Computational Fluid Dynamics (CFD) headingventilation simulations in the Coaltech CM safety project(Meyer, 2015).

3. TEST SET UPS AND VENTILATION OPTIONS

Each test was carried out on-site in an operating continuousminer section, with the ventilation as per standard andimplemented for the operation.

Headings were cut and supported to allow for access asclose as possible around the continuous miner, and the testwas then carried out with the continuous miner and shuttlecar in position, and with all ventilation and spray systems onthe continuous miner in operation.

Numerous test set ups and options were carried out, toensure that as many as possible practical operating situa-tions were evaluated. These included:Mining operations:• Continuous miner operating• Continuous miner not operating• Shuttle car present• Shuttle car not present• Joy CM• Sandvik CM• FCT (flexible conveyor train)

CAS Thomson1, AP Cook2,RM Fourie3

1Anglo Thermal Coal, 2Latona Consulting, 3PanaramaTraining Systems

Developing a protocol to evaluate continuous minerheading ventilation systems using practical on-site measurements

Original paper presented at the 2015 MVSSA Conference


Ventilation mechanisms:

• Full height scoop brattices

• Half height scoop brattices

• Free standing fans

• On-board scrubbers,

- single and double

- straight, angled and right-angled discharge

Heading parameters:

• Long headings 30 m - 41 m

• Short headings 12 m - 24 m

• Box right

• Box left

4. PRESENTATION OF RESULTSVentilation results have been compiled in a comprehensiveinternal document for Anglo Thermal Coal. Ventilation flowmeasurements and results are given as a series of colourFigures, each Figure presenting results for a single test.These are drawn approximately to scale, and show for eachtest as may be applicable:

• the heading

• last through road

• box right or left

• continuous miner

• shuttle car

• fan

• scoop brattice type

• ventilation velocities and directions

• comments

The Figures show the results as measured ventilation directions and velocities represented by small arrows pointing in the direction of the measured flow, with themeasured velocity in metres per second (m/s) beside thearrow.

On the original comprehensive tests, where applicable, measuring positions included up to three readings for heightfrom floor or roof at that point vertically, so as to establishan averaged ¡§dimensional type ¡§ velocity profile.

In addition, each Figure contains main directional flowarrows, areas of turbulence or low flow velocities, and comments. The directional flow arrows are overlaid on theFigure as a semitransparent blue or red arrow, and the turbulent and low velocity areas are shown as semi-transparent ovals coloured yellow for turbulent flow andorange for low velocity.

Turbulent flow is defined as ‘not possible to determine aflow direction’, and low velocity as ‘below 0.1m/s’.

Where possible, the scrubber fan recirculation has been calculated, and this is also included as a comment on theFigures.

5. SCRUBBER FAN RECIRCULATION CALCULATIONS

The scrubber fan recirculation was calculated using the standard practice for the SA industry, derived from the DMRguideline (GME 16/2/1/20. 1994).This requires measurement of the scrubber fan intake quantities and the heading ventilation intake quantities.The calculation used is:Scrubber fan recirculation (%) =100 * [scrubber fan volume (m3/s) – heading intake air volume (m3/s)] / [scrubber fan volume (m3/s)]For example:Scrubber fan volume = 8m3/sHeading intake volume = 6m3/sScrubber fan recirculation = 100 * [(8 – 6)/8] = 2/8 =25%

This recirculation formula does not take into account that insome situations, it is likely that a significant portion of theheading intake air does not penetrate into the heading rightup to the position of the scrubber fan intake on the continuous miner.

Hence in some situations it probably underestimates thescrubber fan recirculation.

6. EXAMPLE RESULTS

There are more than 40 individual Figures from test results,and a few of these are given as means of example.

These Figures are intended as full colour and full page A4format, so some detail is unfortunately lost by reproducingfor this paper.

The examples have been selected to show both long andshort headings, as well as boxing, and different ventilationsystems.

Figure 1 shows a 32m heading, and CM with a straight single scrubber discharge of 4.6m3/s.

Auxiliary ventilation was by means of a half height scoopbrattice, a system that is no longer in use at ATC.

The intake quantity to the heading was estimated from themeasured intake velocities and the available intake cross sectional area as 2.6m3/s, which gives scrubber recirculationcalculated at 44 %.

Figure 2 shows a 32m heading, and a CM with a straightsingle scrubber discharge of 4.6m3/s. A jet fan was installedat 17 m upstream in the intake road from the LTR. The shuttle car was in the typical loading position behind theCM.

The intake quantity to the heading was estimated from themeasured intake velocities and the available intake cross sectional area as 11.2m3/s, which gives scrubber recirculation calculated at (negative) -114%, or as no recirculation.

There is turbulent flow to the intake and return sides of the


CM and at the shuttle car, and an area of turbulence in thefirst few metres of the heading.

Figure 3 shows a 22m heading, with a straight single scrubber discharge of 5.1m3/s. The CM was boxing to theright and a full height scoop brattice was installed.

The intake quantity to the scoop was measured as 3.7m3/s,which gives scrubber recirculation calculated as 28%. Thedischarge quantity from the scoop was measured as 2.9m3/s,which gives scrubber recirculation calculated as 42%.

Figure 4 shows a 25 heading, with a straight single scrubberdischarge of 4.9m3/s. The CM was boxing to the left with noscoop brattice or jet fan installed. The shuttle car was in theloading position behind the CM.

The intake quantity to the heading was estimated from themeasured intake velocities and the available intake cross sectional area as 4.6m3/s, which gives scrubber recirculationcalculated at 6%.

Figure 1. 32m long heading, with half scoop brattice

Figure 2. 32m long heading, with jet fan removed 17m backfrom the heading entrance

Figure 3. 22m heading, box right with straight discharge singlescrubber


several main or significant conclusions. These have beenused by Anglo Thermal Coal to already make informed decisions on their current and recent ventilation practicesforcontinuous miners, and to direct the future risk assessments and evaluations required before any changesare made to ventilation systems or modifications to CMscrubber systems.

The summary conclusions from all the tests are, in brief:

8.1 Headings (all headings beyond 12 m)• Ventilation penetration into any heading is dependent on

the LTR velocity.• LTR velocity should never be less than 1m/s.• Normal LTR ventilation flow penetration into any heading

without a scoop brattice or fan is only effective to a maximum distance of twice the heading width.

• The LTR ventilation penetration can be reduced when thescrubber fan is operating.

• Scoop brattices and / or fans improve the ventilation penetration in headings.

• Scrubber fan recirculation cannot always be confidentlycalculated.

8.2 Long headings (all headings beyond 30m)• All the conclusions for Headings also apply to Long

headings.• Long headings must have auxiliary ventilation, e.g. scoop

brattice, jet fan, force column.

There are areas of low velocity flow around the shuttle car,with the intake air crossing the shuttle car and flowingbelow the return air discharging from the scrubber.

7. COMPARATIVE CFD CALCULATIONS

Input from some of the measured on-site tests was used tocalibrate and verify the CFD results for the Coaltech CMSafety project.

Figure 5 (Meyer, 2014) shows and example of this, which isthe CFD simulation of the heading test shown in Figure 4with the CM boxing to the left. Ventilation flow velocities areplotted on the CFD representation, and some calculatedindividual flow velocities are given as comparisons withactual measured velocities for the same mining operation.

Results such as this have shown the CFD to be a reliable toolfor coal mine heading ventilation simulation.

8. SIGNIFICANT HEADING VENTILATION CONCLUSIONSTO DATE

Although only results from four examples have been given,from all the results to date it has been possible to derive

Figure 4. 25m heading box left with no scoop or jet fan

Figure 5. CFD representation of 25m heading box left with noscoop or jet fan


• Scoop brattices must be correctly installed to ensure thatno ‘flapping’ occurs at the discharge end when the scrub-ber fan is operating as this causes significantly fluctuatingdischarge air velocities.

• In long headings leakage from a scoop brattice is increasedproportionally due to the longer length.

• Scoop brattices achieve better intake air penetration if thebrattice discharge area does not exceed more than 25% ofthe average heading area.

8.3 Boxing right

• With high volume right angled scrubber discharge, the discharge is directly into the heading mostly towards theexcavated face area, resulting in increased scrubber recirculation at the advancing box cut face.

• Straight scrubber discharge, and reduced scrubber volume,combined with use of a scoop brattice, or force fan andduct,significantly reduces recirculation.

• With no CM operating, in an unventilated heading, thebox to the right reduces the ventilation penetration intothe heading to less than 12m - 14m from the LTR.

• Installing a half scoop brattice did not significantlyimprove the penetration from the LTR when boxing right.

• With no CM operating a full scoop brattice should beinstalled.

8.4 Boxing left

• With high volume right angled scrubber discharge, there isweak ventilation penetration from the LTR, and increasedscrubber recirculation.

• With no CM operating, in an unventilated heading, thebox to the left reduces the ventilation penetration into theheading to less than 12 m - 14 m from the LTR.

8.5 Scrubber fan recirculation

Recirculation calculations are possible in some but not all situations. In particular the recirculation cannot be confidently calculated where access to the scrubber fan isnot possible, e.g. cutting in the first or third ‘slot’ cuts, andalso where there are high degrees of turbulence, meaningthat ventilation directions cannot be determined.

9. DEVELOPMENT OF A VENTILATION TEST PROTOCOL

One foremost conclusion of the tests is that not all modifications or changes made to on-board or auxiliary ventilation systems, since the implementation of SIMRACCOL518 (Du Plessis et al, 1999), have resulted in improvements to heading ventilation conditions. This indicated the need for a systematic and repeatable approachfor senior ventilation officials to evaluate systems wheneverchanges have been made or are to be made.

An Anglo Thermal Coal ventilation test protocol is beingdeveloped from the practical aspects of the SIMRAC COL518protocol (Du Plessis and Belle, 1998) and from the individual on-site heading ventilation tests carried out acrossAnglo Thermal Coal collieries by from 2004 to 2015.

It has been derived in such a way that it enables senior ventilation officials to carry out the required measurementsand evaluate the results and relatively quickly identify compliant or noncompliant heading ventilation systems.

Each delivered test report must conclude if the ventilationsystem as tested is compliant or noncompliant, or if it isacceptable or not for the mining conditions tested.

A system is non-compliant and not acceptable if:

• The heading fresh air intake quantity (m3/s) cannot bedetermined.

• The calculated scrubber fan recirculation exceeds 50%.

• The calculated fresh air quantity is less than 0.2m3/sm2 offace area.

• There is excessive turbulent flow, and flow directions cannot be adequately determined.

• Methane concentrations regularly trip the CM

• Dust concentrations regularly exceed 5mg/m3.

The protocol includes all the requirements of the SIMRACCOL518 protocol, but modified to suit practical on-site measurements, and is intended as an support system to anyfinal evaluation system presented by the current CoaltechCM safety project.

10. ON-SITE HEADING EVALUATION AND CALCULATIONS

In addition to the test protocol, the need was identified for arelatively simple immediate on-site method to empower theteam working in a section to check ventilation conditions inthe heading.

As access to the immediate working areas around an operating CM is difficult, or impossible, or not permitted,full ventilation surveys as have been carried out for thesetests are only possible with special previous arrangements,and often only with specialised equipment.

For routine and practical on-site evaluations, two or three (2or 3) positions, depending on the auxiliary ventilation appliances, can be reasonably measured, and that these canbe used to make an immediate on-site evaluation of any CMventilation system.

The two or three measuring positions are:

• The intake quantity at the LTR (including scoop bratticeintake and discharge, scoop brattice with or without a fan,or fan only, or with force duct).

• The on-board scrubber fan intake quantity From these it ispossible to determine the scoop brattice leakage (if applicable) and the scrubber fan recirculation.

Figure 6 is given as an example that can be used to recordthe measured ventilation quantities, as applicable to anyheading, and then for calculations of leakages and recirculation. The example shows auxiliary ventilation with afan, and there are similar record sheets for auxiliary ventilation with a scoop brattice, a force column, or for noauxiliary intake ventilation.


11. REFERENCES

Du Plessis, JJL and Bell, BK. 1998. Mechanical miner environment tests protocol. COL518. SIMRAC.Johannesburg.

Du Plessis, JJL, Bell, BK, Vassard, PS. 1999. Mechanicalminer environmental control: evaluation of ventilation anddust control systems in a ventilation simulation tunnel.COL518. SIMRAC. Johannesburg.

Figure 6. Example of on-site heading ventilation calculation sheet

Meyer, CF. 2014. Verifying CFD simulation results with physical underground measurements. Coaltech Report.Johannesburg.

Meyer, CF. 2015. Optimizing ventilation systems in a coalmine heading for effective methane dilution and controlusing computational fluid dynamics. MVS Conference.Johannesburg.


DC van Greuning, Group Occupational Hygiene ManagerSibanye Gold

ABSTRACT

Sibanye Gold prepared a strategy document to enhance theexisting strategy for its Operations to achieve the MineHealth and Safety Council Milestones for Dust and Noiseissued to the mining industry on 19 November 2014 at theMine Health and Safety summit held in Johannesburg. Thisdocument will therefore discuss the current interventions inplace aimed at achieving the 2003 MHSC milestones as wellas additional interventions to be considered as part of theSibanye Gold strategy going forward to achieve the updatedMHSC milestones issued on 19 November 2014.

To be able to achieve the 2014 issued MHSC milestones by2024, focus needs to be placed on the current controlswhilst consideration will to be given to additional proposedas well as future interventions. With a target of 20%improvement per year, the MHSC target will be reached by2020 after which it can be maintained whilst furtherimprovements to exposure levels could be made. This paperwill discuss the Sibanye Gold strategy to meet the 2014milestones for respirable crystalline silica.

1. INTRODUCTION

The MHSC issued updated Health and Safety milestone targets, replacing the current 2003 milestone targets, to theindustry at the Mine Health and Safety Summit held on 18and 19 November 2014 which has been introduced inJanuary 2015.

The MHSC target for respirable crystalline silica is as follows:

• By December 2024, 95% of all exposure measurement resultswill be below the milestone occupational exposure limit forRespirable Crystalline Silica of 0.05mg/m3 (these results areindividual readings and not average results)

• Using present diagnostic techniques, no new cases of silicosis will occur amongst previously unexposed individuals(“previously unexposed individual” are those unexposed tomining dust prior to December 2008 i.e. equivalent to a newperson who entered the industry in 2009).

The MHSC expects the following activity from industry toachieve these targets:

i. Timely adopt identified leading practices in line with aguideline as per the Leading Practice Pillar of the Culture

The Sibanye Gold noise and dust management strategyto achieve the revised MHSC Milestones issued to the mining industry on 19 November 2014

Transformation Framework (CTF);

ii. Timely adopt identified research outcome in line with aguideline as per the Leading Practice Pillar of the CTF.

iii.Programme of work per objective to be identified, developed and implemented

(Adoption refers to the full process as per the defined MHSCGuideline for Adoption and must be fully inclusive of all stake-holders).

Sibanye Gold is committed to zero harm of its employeesand in so doing, endeavoured in achieving the occupationalhealth targets and milestones issued to the mining industryin terms of the 2003 MHSC milestones, which were prescribed to industry on the 15 June 2003, at the tripartitehealth and safety summit comprising representatives fromGovernment, Organised Labour Unions and Associations andmining employer groupings, and convened by the MineHealth and Safety Summit. This commitment is driven byrecognising that there is a need to achieve greater improvements in occupational health and safety in the mining industry than had been achieved in the past.

With the 2014 milestones being more stringent than thoseissued in 2003, renewed focus, commitment and work toachieve these revised targets is required.

2. SILICOSIS PREVENTION

Gravimetric dust sampling is the core of a silicosis management programme as its results firstly determines thedust dose which an employee as well as the HomogeneousExposure Group (HEG), represented by this individual willreceive. It furthermore also determines the effectiveness ofthe various control mechanisms in place to prevent exposureto silica dust.

Gravimetric dust sampling results provide the opportunity toobtain information related to exposures such as:• Occupational exposure trends• Level of exposure• Working place information• Ranking of exposures in terms of exposed occupations• HEG comparisons• Overexposure investigations could provide information as

to the reason for the overexposure as well as to the typeof control to implement.

• Type of control which could potentially be used.

Gravimetric dust sampling analysis is used to determine thetype of control which could be used to protect employeesagainst silica dust exposure.Original paper presented at the 2015 MVSSA Conference


2.1 Compliance to the 2003 MHSC milestones

Great strides were made towards achieving the 2003 MHSCmilestones, with Sibanye Gold collectively achieving therequired targets however there are some mining units acrossthe operations which had mixed results in achieving thesetargets.

2.2 Compliance to the 2014 MHSC milestones

To be able to achieve the 2014 MHSC milestones by 2024,focus needs to be placed on the current controls whilst consideration should to be given to additional proposed aswell as future interventions.

In 2012 Sibanye Gold introduced a self-imposed target of nomore than 20% of individual samples exceeding a silica dustdose of 0.05mg/m3. This target was adjusted to no morethan 15% of individual samples exceeding a silica dust doseof 0.05mg/m3 in January 2014.

In 2012 Sibanye Gold managed to achieve 15.9% whilst in2013 it achieved 22.5%. With the lowered target of 15% for2014, 18.6% was achieved by Sibanye Gold. As the requiredtargets could not be met it has been decided to use a stepdown approach with annual improvements of 20% to meetthe 2014 milestone target of no more than 5% of individualsamples to exceed the MHSC milestone of 0.05mg/m3 by2024, rather than to immediately attempt to achieve themandatory 2024 target of no more than 5% individual samples exceeding 0.05mg/m3.

The graph in figure 1 below depicts the required annualimprovement of 20% based on the achievement of 18.6%above 0.05mg/m3 for Sibanye Gold in 2014. This improvement target is in line with the MHSC requirementfor safety improvements, so as to ensure that compliance isachieved by 2024.

With a target of 20% improvement per year, the MHSC target will be reached by 2020 after which it can be maintained whilst further improvements to exposure levelscould be made. Individual mining units and metallurgicalunits will have their own targets to meet the annual milestone values as depicted in the graph in figure 1.Starting in 2015 some units however will have to meet amore stringent percentage improvement to meet the proposed 15% above the MHSC target of 0.05mg/m3 whilstthere are also units which are close to or already meetingthis requirement therefore having a required improvementof less than 20%.

2.3 Silicosis prevention interventions

Sibanye Gold has introduced a number of interventions toreduce employee exposure to respirable crystalline silicadust. There has been a downward trend in the TimeWeighted Average (TWA) concentration (dust loading) ongravimetric sampling dust filters per operation since 2008due to some of the silicosis reduction interventions whichwere introduced. The crystalline silica quartz concentration,which determines the dose to an employee, cannot be controlled and it is therefore important to control the liberation of dust underground to ensure that employee

exposure is kept below the occupational exposure limit andmore important the newly introduced MHSC milestone for respirable silica dust exposure.

Below is a discussion of the interventions introduced acrossthe Sibanye Gold operations to reduce exposure to silicadust as well as to meet the 2003 MHSC milestones.

2.3.1 Footwall treatment

The importance of footwall treatment in intake airways mustnot be underestimated. It prevents the liberation of dust intothe atmosphere and limits the exposure of employees toharmful silica dust. To remain effective footwall treatmentwith dust allaying chemicals, which was introduced in 2009,need to be applied on a scheduled ongoing basis. The totalnumber of metres planned to be retreated across all Sibanyeoperations during 2014 amounted to 963 262m.

2.3.2 Haulage sprays

There are various types of spray systems installed across theSibanye Gold operations where specific needs were identified. These sprays are mostly used in intake airwayswhere high velocities have the tendency to remove moisturefrom the footwall causing the liberation of dust into theatmosphere. It has to be properly maintained so as to ensureits ongoing efficiency. The decision whether haulage spraysare required is dependent on a risk assessment addressing aspecific situation or need.

Haulage sprays are site specific based on risk assessmentsand should not be installed on a general basis as it may notsatisfy the specific need which could be at hand.

2.3.3 Protection at main ore pass systems

Up casting ore pass systems, even with operational filtrationsystems, across all operations remain a problem. The reasonfor the up casting ore passes is mostly the lack of a plug ofore kept at the transfer chutes for later bleeding, or in someinstances the absence of transfer chutes causing ore pass systems to remain empty. Empty ore passes form a parallelairway to the downcast system allowing in some cases largevolumes of ventilating air to travel down these and thenentering into intake levels through the open tips. The problem of the up casting tips is aggravated when tippingoperations take place when the ventilating air with elevateddust levels enter into the intake airstreams. Tip covers havebeen installed at some shafts, in conjunction with tip filters,

Figure 1. Graph depicting the proposed annual target to meetthe 2014 MHSC milestones


which are a requirement at main ore passes, in an effort tocontrol this problem. A successful solution to this problemneeds to be further investigated as to the shaft specific reasons which need to identified and engineered out.

2.3.4 Winch covers

Winch covers were rolled out across the operations in orderto protect winch drivers against the liberation of silica dustin their breathing zone with the coiling and uncoiling ofwinch ropes on the winch drums. It has been found that thewinch covers are removed for various reasons with the resultthat some winch drivers are still exposed to silica dust. Thisproblem has been overcome with compliance checks beingdone at winches to ensure that the winch cover is present onthe winch drum guards.

Winch covers should be an item to be checked on the winchdriver’s checklist, whilst supervisors need to ensure thatthese are not removed.

2.3.5 Health Rooms

The Sibanye Gold operations have functional health roomsat the training centres of the various operations as part ofemployee education which includes noise and dust, howeverthere is still a perceived lack of understanding as to the dangers of respirable crystalline silica which is evident whenconsidering work practices in certain instances, for examplethe lack of watering down dusty areas. More work withrespect to employee education and awareness needs to bedone and will be discussed later in the document under section of new interventions.

2.3.6 Silver membrane filters

The accuracy of the gravimetric dust sampling process toultimately determine the dose of an individual is of utmostimportance as any error in the process will result in potentialincorrect dose allocations. Sibanye Gold resorted to the useof silver membrane filters at the beginning of 2013 as partof its drive to improve on the accuracy of gravimetric sampling results.

Until 2012 Micropore Membrane Cellulose Ester (MCE) fil-ters were used for gravimetric dust sampling purposes. Themain difference is that the MCE filters need to be acclima-tised and therefore poorly acclimatised filters may have aperceived higher mass due to the entrapment of residualmoisture in the filter. Silver membrane filters do notneed tobe acclimatised.

2.3.7 Stope atomising sprays

Stope atomising sprays are effective methods of wettingcomplete panels with a water spray after a blast. The spraywhich is installed at the toe of a panel can be installed by asingle person and has been implemented during 2014.

This system protects all persons during first entry after ablast, especially the night shift crew. The use of this is beingfollowed up upon during compliance audits or inspections.

2.3.8 Development waterblasts

Development waterblasts are important to protect

employees after the blast prior to entry into the developmentend. The use of this need to be enforced as it is normallyfound that the waterblast is present however in manyinstances it is not connected to the water supply.

2.4 Updating of silicosis prevention controls

A number of dust control systems are in place and are providing good results in the prevention of employeeexposure to silica dust. There must however be a renewedfocus placed on some of these control systems whilst workpractices as the way at which certain tasks are performed,need to be reviewed. Certain work practices have far reaching consequences in terms of the liberation of silicadust into the atmosphere with the resultant exposure ofemployees.

It is therefore also important for the various mining unitsand metallurgical units to track and manage silica dust exposure at their individual units. This document will provide some guidelines as to the management of dust andnoise at the units.

2.4.1 Dirty material cars

Material cars not being cleaned properly before loading anytype of material or equipment have proven that dust is liberated into the atmosphere when being off loaded fromthe cage on shaft stations. Systems to clean and in someinstances wet the material and the cars need to be employedto prevent this from happening. A typical example of wettingdusty material is the installation of bank sprays wetting thematerial before being loaded into cages.

2.4.2 Cleaning of shafts and shaft areas

Spillage falling down shafts has the potential to contaminatethe intake air flowing into the mine. Cleaning of spillage orthe use of water spraying systems to prevent the liberationof dust into the atmosphere is an important aspect in thedust prevention regime.

Shaft cleaning systems need to be operation specific.

2.4.3 Isolation of main transfer chutes

Bleeding of main transfer chutes has been observed toliberate silica dust into the atmosphere. It is important tohave these isolated as it causes direct contamination of theintake air. Enclosing of transfer chutes need to be site specific.

2.4.4 Dry spillage loading in haulages

Cleaning of mud in drains normally takes place by loadingand then accumulating the mud into small piles normally onthe side of haulage travelling ways. This mud is left in thesesmall piles to dry out after which it will be loaded into ahopper, creating excessive dust as these piles are not alwayswetted down before loading.

This practice needs to be re-assessed, by employing moreeffective ways, such as weeping bags attached to the sidewalls into which the mud can be deposited. It isimportant to discourage the double handling of the drymud.


2.4.5 Stope strike control

The importance of good ventilation must not be underestimated as high velocities carries dust away intoreturn airways before it has time to settle down.

It is therefore important to maintain strike control in stopesto ensure that velocities meet the Sibanye Gold target of1,0m/s to maintain conditions conducive to health and safety.

2.5 New silicosis prevention interventions

Every effort is made to prevent exposure to silica dust byusing tried and tested methods, however it is also importantto investigate interventions and new methods on an ongoingbasis to ensure that the best and latest practical technologyis employed to protect employees against exposure to silicadust.

The most important intervention is to ensure that employeestruly understand the dangers of silica dust and to create anattitude of “how will my health be affected when I need toperform a specific task at hand?”

2.5.1.1 Silicosis awareness month

To create an awareness of the danger of silicosis amongstemployees, a silicosis awareness month was held in April2015. The following formed the basis of the Silicosis awareness month:

• Weekly awareness topic. This was communicated bymeans of a comic system in the various languages used inSibanye Gold which were issued and discussed at all waiting places or meeting areas.

The topic was discussed with all supervisory personnel atthevarious weekly health and safety meetings in order toconvey the same message to their subordinates.

• The appropriate posters were displayed at notice boardsspreading the silicosis prevention message.

2.5.1.2 Silicosis awareness training

Training material at the various training centres are beingaudited and updated where necessary as to ensure thatemployees receive the best quality up to date training.

2.5.1.3 Silicosis Awareness posters

It is important to display awareness posters at conspicuousareas portraying messages concerned with employee health,these must be updated on a regular basis to ensure that itremains effective.

2.5.3 Reclamation in old areas

Gravimetric dust sampling results has indicated that thereare elevated dust doses in old areas where the reclamationof material takes place.

This is as a result of the areas being dry and that no water,in most instances, is available to wet the areas down wherereclamation and vamping are to take place.

Risk assessments with appropriate control measures need tobe done to address this matter and to find practical and

effective means to protect employees against silica dustexposures.

2.6 Silicosis Management

It is important to have systems in place to manage silica dustexposure prevention as the old saying of “if we do not measure, we do not know” is very true.

A system which works well is the establishment of NODUS(Noise and Dust) task team meetings held on a monthlybasis at the Sibanye Gold operations at which progress aswell as issues.

It is furthermore important to understand that there arevarying quartz concentrations at the different operations.

What is important is that based on the quartz concentrationfor a specific mining or metallurgical unit, the maximumTWA concentration (dust load) must be determined toensure that no dust dose above 0.05mg/m3 takes place. Thisneeds to be tracked to ensure that the various control measures remain efficient.

Compliance monitoring to ensure that the various controlmeasures instituted to control silica dust is critical to the success of the silicosis prevention programme.

2.6.2 Sibanye Monthly NODUS feedback meetings

A report is given to the Exec at the monthly NODUS feedback meetings which covers comprehensive informationwith regards noise and dust.The main topics covered are as follows:• Time weighted average concentration (dust load) of dust

samples• Dust sampling compliance• Dust prevention engineering controls• Engineering out the risk• Occupational health data

2.6.3 Monthly Review meetings

High level graphical feedback is given with regards noiseand dust exposure data during monthly Executive reviewmeetings.

2.6.4 Monthly Health and Safety meetings

A feedback presentation with regards the main aspects ofnoise and dust exposure, engineering controls and compliance to these is given on a monthly basis at theExecutive Health and Safety meeting.

2.6.5 Personal dust monitors

Personal dust monitors, which measure all aerosols, areexcellent management tools in identifying elevated dustlevels.

It has been successfully used in the past to identify areas ofconcern. These instruments will be issued to allEnvironmental Engineering staff doing routine undergroundwork. The instruments are used as management tools high-lighting areas of concern, whilst it will also measure the efficiency of controls.


2.7 New technology including new equipmentbeing developed and tested

New technology which may be fit for purpose is being investigated on an ongoing basis and applied should therebe a benefit.

At present, Sibanye Gold is testing the E-Sampler, which is areal time dust measuring instrument whilst a remotewaterblast for development ends is also being tested.Sibanye Gold together with WRE is investigating the manufacturing of a quick clip rose spray for watering down.

2.7.1 E-Sampler

The E-Sampler is a type of nephelometer which automatically measures and records real-time airborne particulate concentration levels using the principle of forward light scatter.

In addition the E-Sampler has a built-in 47mm filter samplerwhich can optionally be used to collect the particulate forsubsequent gravimetric mass or laboratory evaluation.

The E-Sampler combines the excellent real time response ofa nephelometer with the accuracy and traceability of a lowflow manual gravimetric sampler.

The E-Sampler which has the facility to be connected to themine’s telemetry system can be used as a management toolto monitor trends in order to design a dust prevention strategy or it could be used as a system which can start andstop dust allaying spray systems. Both these applications arecurrently being tested within Sibanye Gold.

2.8 MOSH initiatives

Sibanye Gold embraces the MOSH initiatives and is a participant of the MOSH initiative.

Where MOSH initiatives are applicable with value add to theSibanye Gold operations, such initiatives will be adopted.

3. SILICOSIS PREVENTION STRATEGY GOING FORWARD

Sibanye Gold has done much to reduce exposure of itsemployees to silica dust however focus must be maintainedon the task at hand to maintain the successes achieved tolimit the exposure of its employees to silica dust.

To comply with the 2014 milestones, the following strategyneeds be followed:• Maintain and comply with the interventions instituted to

date.• Ensure a proper watering down regime.• Ensure that work practices are such so as to prevent the

liberation of silica dust into the atmosphere.• Employees must be empowered to understand the

dangers and consequences of breathing in silica dust.• Implement additional interventions where applicable and

practical to apply with positive results.• Respiratory Protective Equipment (RPE). Although silica

dust must be controlled at source, there will be situations

where respiratory protection is required to protectemployees against the inhalation of silica dust. Dustmasks and in some instances, respirators, will be providedfree of charge to employees for respiratory protection.Respiratory Protection Equipment needs to be evaluatedon an ongoing basis as to ensure that the best protectionis afforded to Sibanye Gold employees at all times.

4. SUCCESS OF THE SILICOSIS PREVENTION PROGRAMME

The MHSC target which requires that by December 2024,95% of all exposure measurement results will be below themilestone occupational exposure limit for RespirableCrystalline Silica of 0.05mg/m3 is attainable. The SibanyeGold operations have taken great strides in reducingemployee exposure to silica dust and not much more isrequired to be done in terms of controlling the liberation ofsilica dust into the atmosphere.

What is important, however, is that every employee takeresponsibility to ensure that any control measure institutedto prevent the liberation of silica dust be applied and maintained in order to prevent exposure to silica dust. Thesuccess of the Sibanye Gold Silicosis prevention programmeis therefore dependent on the participation of all its employees.

REFERENCES

MHSC milestones issued in November 2014.


Mine Ventilation Society of South AfricaTel: +27 11 482-7957 /

Email: [email protected]

all the workings were ventilated and cooled all the timeeven when there were no employees or activities being performed underground. However, an increasing cost ofelectricity and issues such as load shedding compels theindustry to look closely at means to save on electricity costs.Automation could well be a means of achieving considerablereductions in these costs.

2. BACKGROUND

The year 2008 can be seen as a defining point for a new era,where the electricity supply and low tariffs could not beguaranteed in South Africa any longer. The tariffs increasedby more than 200% and are expected to increase further infuture (figure 1). This is becoming a threat to the economicviability of mines, especially underground precious metalmines.

Figure 1. Average electricity price in South Africa (Ramayia,2013)

The mining sector is the second highest consumer of electricity with precious metal mines being accountable for80% of the total power (figure 2&3).

Figure 2. Energy consumption by sector (Thopil and Pouris,2013)

The shortage of electricity and increasing tariffs will rendersome of the mining project unviable, especially undergroundprecious metal mines. This will have a snowball effect on theeconomy, which relies heavily on mining to earn foreignexchange.

Furthermore, more emphasis is placed on the responsibilityand accountability of mine owners in terms of health andsafety of which a healthy working environment is a vital

Electricity savings in automated minesE.M. Mochubele1, D. Bakker1 and D. Farlam2

1School of Mining Engineering, University of theWitwatersrand, 2South Deep Gold Mine

ABSTRACT

Reducing electricity costs of ventilation and cooling in deepprecious metal mines through automation was investigated.The reason for this is that automated mining machinery mayendure higher rejection temperatures in production zoneswhere only equipment operates. This increase reduces theheat conduction transfer as the difference in temperature ofthe airway surface and the rock would be smaller whichreduce the amount of air and cooling required.

The study looked at power demand for automated mine(unmanned) where only equipment operates and the rejection temperature in production zones was set at 40oC(db). This was compared to power demand in similar mechanised (manned) operations where the rejection tem-perature was set at 27oC (wb) to create a thermally accept-able environment for workers.

These parameters were applied to a theoretical gold minedesigned using VUMA software package. The modelled minewas set to have a maximum depth of 2800 metres and aproduction rate of around 200kt per month with similardesign environmental conditions as the South Deep Mine inthe Westonaria area.

The results showed that increasing the rejection temperatureto 40oC in an unmanned scenario theoretically reduced theelectricity cost for cooling and ventilation by more than 50%compared to the manned scenario, translating in an annualsaving on ventilation and cooling costs of R71 million.

The capital cost of automation was beyond the scope of thiswork. However, it suffices to say the savings realised in ventilation and cooling costs will reduce the payback period.

1. INTRODUCTION

A compelling reason for considering automation is the possibility of achieving considerable savings in electricitycosts.

South African precious metal underground mines need touse electricity efficiently in order to reduce current energydemand, rising cost and associated carbon footprint. Mineventilation and cooling systems require electricity to moveair and cooling fluids in underground workings to createacceptable environmental standard for workers. These systems account for a significant portion of energy consump-tion. Historically, electricity cost was low and did not have anegative impact on the operating cost of a mine. Hence, themines could use “brute-force” ventilation strategies, where



component. These challenges and others are forcing themining industry to look at automation.

One of the major day-to-day challenges facing South Africanunderground mines is heat. The temperature increases dra-matically as the mining depth increases.

This causes great difficulty in creating and maintaining comfortable working conditions for both humans andmachines (Eskom & Gold Fields, 2010). Hence, the deeplevel mines adopt unique cooling methods which requirepower to function. Typical electricity cost drivers in gold andplatinum mines are illustrated in Figure 4. It is clear fromthe graph that ventilation and cooling combined is thelargest contributor to electricity cost. This is the reasonmines are looking at initiatives to reduce power demand dueto ventilation and cooling.

Figure 4. Distribution of energy costs between the various mineprocesses (Anon., 2008)

There are two common strategies to address this challengenamely Ventilation on Demand (VOD) and Cooling onDemand (COD). These strategies aim to supply air and cooling when required. This means that when air or coolingis not required there would be cost saving as power requiredto drive fans and refrigeration plants would be reduced.Both VOD and COD need a very strong communication andtracking system whereby workers and equipment locationare known on a real time basis. Over and above to this, sen-sors must continuously feed into the communication systemto inform environmental condition of working areas. When

all this information is known then VOD and COD can beapplied optimally and safely.However, full potential has not been realised due to the fol-lowing reasons:• Initiatives not being suitable in the South African context• Inability to reduce amount of air ventilation and cooling

because of the presence of employees in production areas.

The second reason led to this research whereby a fully automated mine was modelled to explore the possibilities ofreducing the electricity demand in underground mines.

In the context of this paper the much higher operatingequipment temperatures are the main reason why mines areconsidering automation, as ventilation and refrigerationcosts can be cut considerably. The recent available data supplied by leading equipment manufactures indicate thatthe design operating temperature can go up to 55OC.

3. METHODOLOGY

A hypothetical mine was modelled in collaboration with theSouth Deep Gold Mine ventilation specialist to quantify thebenefits of increasing rejection temperatures in automatedmines. The model focused on massive ore-bodies wheremechanisation has been proven. The modelled mine wasbased on a simplified version of South Deep Mine. Two scenarios were simulated namely mechanised (manned) andfull automation (unmanned), and a comparison was madein terms of ventilation and cooling required. The mechanised scenario takes into account that there areemployees operating equipment in production areas while inautomation only machines are in the production areas.

The software used to develop this model was VUMA. Thisplanning tool is important to predict and optimise futureventilation and cooling requirements. It is especially usefulwhen dealing with complex networks that cannot bereduced to simple series or parallel circuits. However, it mustbe noted that VUMA is not a magic panacea. It does notreplace a good working knowledge of basic ventilation theory and practice.

The planning of ventilation in this report followed a systematic approach. This approach is made up of six phasesin order to develop optimum ventilation system (Figure 5).The critical phases for the study were phase 1- 4 in order todemonstrate the cost saving on electricity demand on ventilation and cooling due to automation.

3.1 Mining Method

The mining method chosen for this study was geared for athick deposit on the eastern part of the Witwatersrand basinas shown in figure 6. There are two production sectionstermed corridor 1 and 2. Typical ore extraction in corridorsincorporates a number of mining methods such as de-stress,long-hole stoping and bench and drift. Backfilling is usedextensively to address rock mechanics challenges but alsoassist in increasing air utilisation and efficiency (Chadwick,2011).

Figure 3. Energy consumption in the mining sector (Deloitte,2009)


Phase 1: Determine mining method and rate of production

Phase 2: Define acceptable environmental standards

Phase 3: Calculate heat increases, gas emissions and dust production

Phase 4: Calculate air and refrigeration requirements

Phase 5: Optimise alternatives (ventilation and refrigeraion system)

Phase 6: Select system

Figure 6. Generalised Witwatersrand East-West section showingthe stratigraphy of the ore-body (Jones, 2003)

The model takes a snap shot at a steady state production ofaround 200 000 tons per month including development tonnage for both manned and unmanned scenarios. Themodel assumes the following assumptions shown in Table 1for mining.

Table 1. Mining assumptions

Figure 7 shows the designed mine layout with intake air-ways shown in blue and return airways in red. The mechanical workshop and control room for both scenarios,manned and unmanned, were placed underground at level90. The refrigeration machines, using refrigerant R134a, forboth scenarios were placed closer to the up-cast shaft toavoid leakage of a refrigerant which could eventually findsits way into the combustion cycle of diesel engines and produce toxic gases.

According to Brake (2001) when the diesel engine intake airis mixed with refrigerant R134a and gets into the combustion chamber, it has a potential to be converted intoa highly toxic and corrosive gas, hydrogen fluoride.

Figure 7. Schematic drawing of modelled mine- air-intakes(blue) and RAW (red)

3.2 Model validation

The hypothetical model of the underground operations wasvalidated by comparing the results generated by VUMA software and calculated figures of the VRT and auto-compression. It was also validated by using actual measuredvalues from South Deep Mine.

The air velocities in various airways were gauged against therecommended criteria. The percentages of heat sources inthe model were compared with the ones in South DeepMine.

3.3 Acceptable environmental conditions

The project focuses on a thermally acceptable environmentfor both mechanised and automated scenarios. The rejectionwet bulb temperature (wb) for the mechanised mine (i.e.manned) is set at 27.5OC and 32OC dry bulb (db). The automated mine (unmanned) rejection temperature was setat 40OC (db) in the working areas as the machines are notaffected by wet-bulb temperatures provided that the air isnot saturated. However, the temperatures in the travellingways to the workshop and the workshop itself have been setat 27.5OC (wb) and a 32OC (db) because of two reasons,namely; employees working in the workshop and for equipment in the control room.

South African mines are required to draft and implement amandatory Code of Practice (CoP) based on guidelinesissued by the chief inspector of mines in terms of section 9.2of the Mine health and Safety Act. A summary of the thermal stress CoP showing temperature ranges, interpretation and actions required is shown in Table 2.

The mandatory CoP on thermal stress is a measure to indicate what steps have to be taken in order to avoid riskassociated with heat.

3.4 Heat increases

The total heat load for manned and unmanned mining scenarios obtained from the model were around 48 000kW

Parameters Dimensions

Depth (km) 2.8

VRT(average in OC) 50

Steady state Production per corridor (kton/month) 98.5

Number of corridors 2

Steady state production (kton/month) 197

Tunnel sizes (m) 5.5 x 5.0 and 5.5 x 5.5

Figure 5. A systematic approach to ventilation planning(Burrows et al., 1989)


and 40 000kW respectively. Both manned and unmannedscenarios had the same heat sources with varying degrees ofcontribution as shown in Figure 8 below and reasons for thedifference are provided.

Figure 8. Heat load sources and contribution for manned andunmanned

The difference in auto-compression heat contributionbetween manned and unmanned scenarios was due to thefact that heat generated by autocompression is a function ofmass of air taken underground.

The rock geothermal temperature also contributed differently towards heat load for both scenarios because ofthe different prevailing surfaces of airways temperatures forboth scenarios. The difference of temperatures of the rockand surface of airways is a function of heat conductiontransfer. Hence, there is a difference of heat load contribution due to rock geothermal temperatures.

The difference in heat load contribution by to vehicle(s) wasdue to the assumption made in the model that the shifteffective utilisation and machine utilisation would be higherin an unmanned scenario compared to manned scenario.

3.5 Air and cooling required

3.5.1 Air required

The total amounts of air required to create a thermallyacceptable environment were 923kg/s (1000m3/s) at a pressure drop of 5.3kPa for the manned scenarios and 652 kg/s (706m3/s) at a pressure drop of 2.2kPa for theunmanned respectively. The pressure drops and associatedair quantities assisted in validating the model as they obeythe fan law, P = RQ2.

The ventilation factors for the manned scenario were

determined as 4.7kg/s/kt/month and for the unmanned2.2kg/s/kt/month.

3.5.1.1 Main fans selected

Four main fans were selected with twin speeds to be able tosupply air for both manned and unmanned scenarios andwere located on top of the up-cast shaft.

This is different from the current practice of installing fixedflow main fans. This would ensure air flow at all timesunderground as the likelihood of all four fans mechanicallyfailing at the same time would be unlikely. Centrifugal fanswere chosen for this study as they have a reputation of beingrobust and reliable. These fans are designed to cater for boththe manned and unmanned scenarios. This would be ofadvantage especially for the unmanned scenario in an eventof emergency whereby workers are expected to enter theproduction zone. The fan speed would be increased to thetop to create an acceptable environment for workers. Thefan speed for manned and unmanned scenario was found tobe 740 rpm and 510 rpm respectively. The results are asexpected as they are in line with fan laws when connectedin parallel. The pressure remained the same and the sum ofair volume of all fans correlated with the volumetric flowrate of the system operating point for both scenarios. Whenplotted on a graph, it was confirmed that the calculations forelectrical power required were correct.

3.5.1.2 Auxiliary fans

In addition, auxiliary fans were installed in working areas toensure a supply of adequate air. The manned scenariorequired a total number of 79 auxiliary fans with total inputof 3985kW while the unmanned required 108 fans with atotal motor rating of 2940kW. The higher number ofauxiliary fans required was due to the number of workingareas and use of smaller fans in the unmanned scenario.

3.5.2 Cooling required

The results from the model revealed that the manned scenario required a total cooling capacity of 36 000kW andthe unmanned 11 000kW. The strategy that was adoptedwas to first cool the bulk of the air on surface (primary cooling) to overcome auto-compression and create winterconditions during summer.

Secondly cool the air underground to derive maximum ben-efits of positional efficiency (secondary and tertiary cooling).The cooling stages and splits of the cooling are shown inTable 3.

Table 3. Cooling stages and capacities

The surface refrigeration plant was meant to only operate inhot seasons as the winter season provides cold air for under-ground mine. This means it operates for nine months and isswitched-off for three months. A similar cooling system wasused for unmanned though with a smaller capacity.

Cooling stages Manned UnmannedPrimary(kW) 25 000 10 000Secondary (kW) 10 500 1 000Tertiary (kW) 500 0Total 36 000 11 000

Category Temperature Interpretation General Actionrange (OC)

A twb>32,5 Abnormally hot. Risk assessmentUnacceptable risk required before allowingof heat disorder work

B 29 < twb [ 32.5 Potential heat Heat stressdisorder Management (HSM)

mandatory

C 27.5<twb [ 29 Economic range for HSM mandatoryacclimatized workers

D twb [ 27.5 Risk of heat disorders No special precautionsis minimal for both Temperature monitoringunacclimatised and acclimatised workers

Table 2. Thermal stress Code of Practice (DME, 2002)


4. ANALYSIS

4.1 Effect of automation on ventilation costs

In this paper the impact of increasing the rejectiontemperature to 40OC was assessed in an automated(unmanned) scenario at a maximum depth of 2800 metres.Then the power demand was compared with a conventionally manned scenario.

The results proved that automation in an underground minehas the potential of reducing electricity cost of ventilationand cooling by more than 50%. For example, the productionrate of about 200 kilo-tons per month yield an annual costsaving of R71 millions on electricity. The overall results ofthe calculated costs of electricity required in relation to thetonnage are shown in Table 4 for the two scenarios.

The annual tonnage of manned scenario was 2.36 milliontons at an average cost of R40.93/ton of ventilation andcooling electricity cost. This translated to annual cost ofaround R97 million. On the other hand, the annual tonnageof unmanned scenario was 3.54 million tons at an averagecost of R11.04/ton of ventilation and cooling electricity cost.The paper looked at how much would the annual cost ofproducing 2.36 million tons in an unmanned scenario. Theannual ventilation and cooling electricity cost came toaround R26 million. Hence, there would be a saving of R71million on electricity.

5. CONCLUSIONS

The power crisis and corresponding rising cost thereof experienced since 2008, created a ‘paradigm shift’ in termsof electricity use in South Africa. An underground preciousmetal mining business model is sensitive to electricity availability and tariff increases. Apart from this, there are anumber of challenges facing the mining industry such asproductivity, environmental impacts, skills, standardisation,costs and health and safety. Hence, the industry around theglobe is pursuing automation to address these multiple challenges.

Though automation has been a highly topical issue in recentyears, no one has seriously looked at how it will impact onthe electricity demand on ventilation and cooling. This studyhas presented a different approach in reducing electricitycost in underground ventilation of gold and platinum mineby looking at the introduction of automation and increasingrejection temperature.

The study has shown hypothetically that the ventilation andcooling electricity cost could be reduced by more than 50%in a precious metal mine producing 2.34 million tons perannum at a maximum depth of 2800m. The electricity costsaving for this study was R71 million.

It is important to note that the overall profitability of a minecannot be based on this study alone because it excludes thecapital cost of the automation system.

However, it suffices to say the payback period will be shortand profitability will be improved.

6. RECOMMENDATIONS

The South African mines need to adopt automation in orderto realise cost saving and improve productivity. There is nodoubt that automation will affect jobs. It is imperative toengage with the workers unions in terms of automation andhow it will affect employment. Implementation of automation needs a gradual approach as this will providetime to the upskilling of employees and to consult and negotiate with all the stakeholders.

7. FUTURE WORK

While this report demonstrates the cost saving benefits ofincreasing rejection temperature and that the model is ableto predict power requirements, the study is only a first steptowards the development of an accurate full dynamic modelof an underground automated mine. The first priority infuture work is to evaluate the automation sensors and communication systems in South African mining environment. Secondly work must be done on tribology toassess wear and tear of equipment in a hot environment.Thirdly detailed study must be done in terms skill and training required prior to the implementation of automation.

8. REFERENCES

Anon., 2008. Mine Energy Guidelines. [Online] Available at:

Manned

SUMMARY Power manned (kW) Manned Annual cost (ZAR)

Surface Main fan 6705 37 900 049

Underground auxiliary fans 3985 22 526 520

Surface BAC 5938 19 921 488

Underground BACs 4896 16 428 118

Total Annual cost 96 776 174

Average monthly cost 8 064 681

Average electricity price (R/kWh) 0.65

Average kWh per month 12 407 202

Tonnage per month 197 054

Average kWh per ton 63

Elec. Cost per ton 40.93

Unmanned

SUMMARY Power unmanned (kW) Unmanned Annual cost (ZAR)

Surface Main fan 2037 11 513 034

Underground auxiliary fans 2940 16 619 314

Surface BAC 2792 9 369 183

Underground BACs 484 1 622 802

Total Annual cost 39 124 333

Average monthly cost 3 260 361

Aver electricity price( R/kWh) 0.65

Average kWh per month 5 015 940

Tonnage per month 295 379

Average kWh per ton 17

Elec. Cost per ton 11.04

Table 4. Summary of ventilation and cooling electricity costsfor all scenarios


http://conferences.ufs.ac.za/dl/Userfiles/Documents/00000/556_eng.pdf [Accessed 1 April 2014].

Burrows, J., R, H., Holding, W. & Stroh, R., 1989.Environmental Engineering in South African Mines. s.l.:TheMine Ventilation Society of South Africa.

Brake, D. J., 2001. The application of refrigeration in mecha-nised mines. Australia, AusIMM.

DME, 2002. Thermal stress guideline for the compilation ofa mandatory code of practice, Pretoria: DMR.

Eskom & Gold Fields, 2010. Case Study Mining fans.[Online] Available at:http://www.ameu.co.za/Portals/16/Documents/EEDSM%20and%20Renewable%20Energy/Eskom%20Case%20Study%20129938%2020Mining%20Fans.pdf [Accessed 21 May 2014].

Deloitte, 2009: The Economic Impact of Electricity PriceIncreases on Various Sectors of the South African Economyhttp://www.eskom.co.za/CustomerCare/MYPD3/Documents/Economic_Impact_of_Electrcity_Price_Increases_Document1.pdf [Accessed 21 May 2014].

Eskom, 2014. Electricity Tariff and charges, Johannesburg

Ramayia, J., 2013. NERSA allows yearly 8% electricity priceincrease for 2013-2018. Urban Earth, 7 March.


Thopil, G. A. & Pouris, A., 2013. International positioning ofSouth African electricity. South African Journal of Science,Volume 109.

Mine Ventilation Society of South AfricaTel: +27 11 482-7957 /

Email: [email protected]

In-Stope dust control at Beatrix Gold Mine

ABSTRACT

The risk of silicosis associated with the South African goldmining industry has been well documented over the pastcentury. In recent studies silicosis was also identified as acontributing risk factor to other health-related illnesses.Workers suffering from silicosis and HIV have shown a significantly increased risk of TB - as much as 15-fold compared with healthy workers. As part of the resolutionsmade at the 2003 elimination of fatalities milestone settingand as required by the revised 2014 Mine Health and Safetymilestones, continued efforts must be made to implementimproved dust control measures. Through the years variousmeans of dust control within our mines have been identifiedand implemented. The basis of many of these controlsremains the use of water to either suppress airborne dust orprevent dust from becoming airborne.

One of the more difficult areas in which the risk of airbornesilica dust remains significantly high is within the stope areaof a mine. The risk of dust exposure in stopes was identifiedin most of the studies completed by the Industry, and onmines. Most mines still recommend watering down at thebeginning of a shift and during a shift within the stope horizon as the main control. At the Beatrix operations thesepractices remain key to safe work practices, although additional controls have been investigated and implemented.One of these controls is the provision of winch covers andthe second identified control is the use of stope atomisersprays.

In this paper the use of a stope atomiser spray is describedtogether with a preliminary quantification of the impact thishas on worker exposure. From personal exposure concentrations obtained during the control study it is clearthat a significant reduction in worker exposure is possiblewhen effective in-stope dust control is implemented. Anaverage reduction of between 72.6 and 85.3% in the time-weighted average (TWA) quartz concentration was observedduring the trial. The combined average reduction in theTWA quartz concentration across all occupations was calculated to be 79.2%. When comparing the different occupations, in-stope team members are the occupation withthe highest average exposure, although this is still well within the currently legislated occupational exposure limits(OELs).

It was also concluded from the results and the physicalobservations made that the application of this technologywill be beneficial not only for operational stopes, but alsoduring vamping operations. It is therefore anticipated thatthe use of stope atomiser sprays should also reduce the

potential exposure of vamping crews to respirable dust significantly.

1. INTRODUCTION

The risk of silicosis associated with South African gold mining industry is well documented and many studies havehighlighted the continued presence of silicosis, as well asadditional associated health risk factors that are unique tothe South African gold mining sector. Silicosis is an incurabledisease with a number of recognised complications such astuberculosis (TB), loss of lung function, severe lung fibrosisand lung cancer. Exposure to silica dust alone is a risk factorfor TB and the presence of human immunodeficiency virus(HIV) and silicosis has been shown to increase the risk of TB15-fold, this being a serious health concern given the prevalence of HIV in South Africa (National Institute forOccupational Health, South Africa, http://www.nioh.ac.za/?page=dust_projects&id=144).As part of the tripartite initiatives, the mining industryagreed to a new set of industry milestones in 2014 to beachieved by 2024 (Mzisa, 2014). The milestones applicableto the hard rock gold mines are stated below:• By December 2024, 95% of all exposure measurement

results will be below the milestone level for respirable crystalline silica of 0.05mg/m3 (these results areindividual readings and not average results).

• Using present diagnostic techniques, no new cases of silicosis, pneumoconiosis or coal worker’s pneumoconiosiswill occur among previously unexposed individuals.

Where “previously unexposed individuals” are those unexposedto mining dust prior to December 2008, i.e. equivalent to anew person who entered the industry in 2009.In the SIMHEALTH 606 study conducted during 2000 and2001 (Churchyard et al. (2003) the exposure of workers wasinvestigated. It was concluded from this study that the following occupations, in descending order of risk, weremost at risk:• Mining crews in stopes• Team leaders• Drill operators• Scraper winch operators• Loco drivers and crews

In this study (Churchyard et al., 2003) stated that theirresearch supported the conclusions of Hnizdo and Sluis-Cremer (1993) that a reduction of the quartz OEL from0.1mg/m3 is required to reduce substantially the risk of silicosis. The researchers in this case study concluded thatthe earlier (1993) South African studies and their findingsboth suggest that a reduction of the OEL for exposure toquarzitic dust to at least 0.05mg/m3 would be necessary toachieve such protection.

A summary of the shift exposures for different occupationsfrom this study is shown in Figure 1.

JJL du Plessis1, MI van der Bank2

1Associate Professor, University of Pretoria, Department ofMining Engineering 2 Environmental Engineering Manager,Beatrix Gold Mine



Figure 1. Findings from SIMHEALTH 606 - Shift exposures(courtesy of Churchyard, et al. 2003)

From Figure 1 the range of exposures (minimum to maximum exposures) reported for some of the occupationsis evident and as such the employees associated with theseoccupations can be deemed to be at risk. Alternatively, thereported concentrations indicate that during different activities within an occupation there is a potential risk ofoverexposure. These findings also indicate that the controlsimplemented at the time did not reduce exposures effectively throughout a full mining cycle.

In a follow-up study by Biffi and Belle (2003) the quantification of dust sources in underground mines wasattempted. Table 1 summarises their findings in the goldindustry.

Table 1. Dust concentrations in stope faces (Biffi and Belle,2003)

From the table it is clear that the concentrations measuredduring the study covered a wide spectrum, with the minimum and maximum concentrations differing considerably. The quartz concentrations reported in thisstudy were also significantly different for the differentregions.

Unfortunately, no measurements were done during thisstudy in the Free State gold fields, which are the focus of thepresent study.

In this study they also attempted to quantify the dust concentration associated with scraping (dust source) activity.These were unfortunately only done for the two platinumoperations included in the study. The results are shown inTable 2.

Although this study was not conducted in a gold mine it isincluded to demonstrate the potential additional dust levelsassociated with scraping. This indicates that scraping canresult in an increase of between 0.54 and 1.19mg/m3.

A master’s study was conducted by Mike Kemsley (Kemsley,2008) on two Free State gold mines focusing on the exposure of rock drill operators. Results indicated that rock

drill operators using pneumatic percussion rock drills areexposed due to the very nature of the drilling process whererock is pulverised and dust liberated, even when wet drillingis practised.

In this study it is reported that the TWA dust concentrationvalues found were between 0.69 and 0.22mg/m3 for mines1 and 2 respectively, with an average of 0.46mg/m3 forboth. The average quartz percentage was determined to be25.45% for mine 1 and 38.49% for mine 2, resulting in anaverage of 30.67% for both mines. The study was concludedby comparing the results obtained against the different OELlevels set for quartz. When comparing the individual samples against the OEL of 0.1mg/m3 it was found that 32%of all rock drill operators sampled were potentially overex-posed. When using the proposed OEL level of 0.05mg/m3,potentially 72% of the rock drill operators sampled wereoverexposed. Based on these results, the study concludesthat rock drill operators working without appropriate respiratory equipment will be overexposed and thereforepotentially suffer ill health as a result in the long term.

Through the years a variety of dust control methods havebeen identified and implemented to suit South African goldmines. Stanton et al. (2006) identified industry’s best dustcontrol practices for different commodities. In this study, abrief overview of the major dust sources is given and appropriate dust control measures and practices aredescribed. The basis of many of these controls remains within the context of using of water to either suppressairborne dust or prevent dust from becoming airborne.

The outcomes form these studies support the view that stopeareas of gold mines pose a higher risk of exposure to air-borne silica dust. In most of the studies presented so far, thisrisk was identified despite the fact that most of the minesstill required watering down at the beginning of and duringa shift as the main control. At the Beatrix operations thesepractices also remain in place, although additional controlshave been identified and implemented over the recent past.From previous studies at Beatrix operations it is clear thatwatering down of the stope and development areas, especially during re-entry examination and face scrapingoperations in stopes, remains ineffective. In a presentation ofthe results from one such study, Van Greuning (2013) listedthe top 20 most-exposed occupations at the Beatrix operations as shown in Figure 2.

From this figure it is clear that the top five occupations listedas potentially being exposed to silica dust are within thestope area, indicating that further and additional controlswithin this area need to be investigated, trialled and implemented. There is also still a very good correlationbetween these findings and those reported in the

Stope face Min Max Ave Quartzconcentration concentration concentration concentration(mg/m3) (mg/m3) (mg/m3) (%)

West Wits 0.57 1.40 0.9 9.92Vaal 0.41 4.22 1.69 39.05

Stope face Min Max Aveconcentration concentration concentration(mg/m3) (mg/m3) (mg/m3)

Platinum 1 0.71 1.51 1.19Platinum 2 0.25 0.92 0.54

Table 2. Dust concentrations from scraping (Biffi and Belle,2003)


SIMHEALTH 606 (Churchyard et al., 2003) study, as shownin Figure 1. Thus although the level of exposure may havereduced over time, the at-risk occupations have remainedthe same for more than a decade.

Mines have implemented a number of initiatives over theyears in an attempt to improve the effectiveness of dust controls implemented and thus reduce the potential of worker exposure.

Some of these initiatives implemented at the Beatrix Mineare listed below (Van Greuning, 2013):• Establishment of the Project 4 M (Du Plessis and Pienaar,

2009), which was an attempt at the holistic managementof identified occupational hygiene risks as described by theMine Heath and Safety Council Industry Milestones of2003 (Pienaar and Du Plessis, 2009)

• An improved gravimetric dust sampling strategy, including increased and improved silica content measurements

• Increased silicosis awareness

• Improved dust control measures:

. Tip filtration

. Footwall treatment

. Introduction of winch covers

. Use of tip covers

. “Boxing” of transfer chutes

. Use of water prays:

- Shaft bank sprays

- Haulage sprays

. Improved watering-down regime during the shift

. Development and implementation of water-blasts

. Use of stope atomiser sprays

In an attempt to alleviate the identified dust problem withinthe stope area, it was decided to conduct a study to identifythe more effective practices, as well as to identify additionalcontrols that could be used within the stope area. During thesecond part of the study, the value of implementing an in-stope water-blast was investigated. The study included afield trial to determine the effectiveness of in-stope water-blasts in reducing worker’s exposure to silica dust in thestope face environment.

2. UNDERGROUND STUDY

As part of this study underground in-stope visits were under-taken and observations were recorded listing the methodsand practices currently employed during first-entry examinations and during the shift, especially with respect towatering down.

From the historical and current exposure measurement datathe constant overexposures of winch drivers were identified.These overexposures were noted mostly during the nightshift.A summary of the observations made during the under-ground site investigations is given below:• In most cases watering down is done with an open-ended

hose, which can result in dust being liberated into the atmosphere during the watering-down activity.

• The “watering-down tool” (spray gun) currently in use, iseffective when used correctly, but is very time-consuming,and for this reason, watering down is not always done effectively.

• The night-shift crew normally consists of only two or threewinch drivers and a team leader. Their normal modusoperandi is to first get their rigging installed and in anumber of instances started work without watering down.When questioned they claimed that to water down effectively is too time consuming.

• The perception of the crew members is that as they arepositioned on the intake-air side of the panel beingcleaned, they are not exposed. They do not consider thatthe liberated dust could contaminate downstream workingpanels (working in the stope return air) as stopes are oftenventilated in series.

• When watering down is done before scraping is started,there is limited benefit, and after scraping has been donefor a few minutes there is very little evidence of any benefit or for that matter of any watering down havingbeen done at all.

• Watering down during scraping and loading operations isvery seldom practised underground.

With this in mind it was decided to use the water-atomisingdevice, similar to a development water-blast, as a means ofwatering down before and during dust-creating and liberating activities underground. This will also remove theadditional human/equipment interface requirement foreffectiveness.

3. DESCRIPTION OF THE STOPE ATOMISER SPRAY

The device chosen for use in the trial study as a water-blastwas a TerrablastTM unit. For its operation the unit uses bothwater and compressed air to atomise the water droplets.One of the identified advantages of the device is that it usesan 8 mm nozzle, therefore not requiring additional finewater filters. The manufacturer claimed that none of theoperational units at other operations was blocking and thatthe large aperture of the actual nozzle being used did notrequire additional filtration.

Figure 2. Top 20 exposed occupations (courtesy van Greuning,2013)


In general water atomisers in use in mines require goodquality water, high water pressures and filters to preventblockage. The deployed unit requires a water flow rate of0.75l/s and normal mine water pressure, and connectionthrough using a standard 25mm PVC hose connection provides sufficient flow and pressure for effective operation.The photos in Figure 3 show the venturi water-blast (single-nozzle unit) with the individual water and air inlets,each with its own valve.

Figure 3. Venturi water-blast (single-nozzle unit) - Water andair inlets

Figure 4. Performance curve for the single-nozzle stope atomiser spray (courtesy Terramin, Van Schoor 2014, personal communication)

Figure 4 shows the optimal operating point. This is when thecompressed air supply is between 4 and 6 kPa, with waterconsumption of between 250 and 500l/h (maximum). If awater flow rate of 250l/h and 500l/h (See Figure 4) isassumed, it can be calculated that the associated water flowrate will be 0.069l/s and 0.139l/s when a single-nozzlewaterblast is used.

4. UNDERGROUND SITE

During the experimental design it was decided to identify aworkplace that could be considered as the potential worst-case scenario to trial the unit’s effectiveness. The positions ofthe individual venturi water-blasts were chosen to ensureproper watering down of all areas in the stope without wasting any resources through overdesign. The main objective was to demonstrate that one could achieve thedesired dust concentration results within the whole of thestope area.

The identified workplace consisted of a stope area with twomining panels, using six winches to clean the two stope faceareas.

The plan view of the trial site with the position of the installed winches is shown in Figure 5.

Figure 5 Plan view of the underground trial site In the planview the positions of the stope atomiser sprays, ventilationcontrols and winch positions are shown. The airflow direction is shown by the blue arrows. The specific layoutchosen is typical of an old mine where numerous old remnants are being mined and is definitely not an ideal sitewhen ease of operation and potential product success areconsidered. In total, three stope atomiser sprays wereinstalled, assisting airflow as well as providing effective areacoverage.

Figure 5. Plan view of the underground trial site

Figure 6 shows a photo of a typical installation of an atomiser spray in a stope at the underground trial site. Theease of installation, as well as both the water and compressed air pipes is, shown. The atomised water mistleaving the water-blast is clearly seen. This type of water-blast has the additional benefit of inducing airflow by meansof the venturi design, utilising the compressed air and waterpressure effectively.

5. METHODOLOGY

The methodology used to evaluate the effectiveness of theimplementation of the stope atomiser spray was to do acomparative study of the personal respirable dust exposurelevels of the different occupations of in-stope workers beforeand after the installation of the in-stope waterblasts.

The personal exposure measurements of several occupations(Beatrix Mine Mandatory Code of Practice) were taken usingstandard on-mine sampling and analytical techniques for atrial period of eight weeks.

The definition of personal sampling is when the dust samplecollected in the breathing zone of a worker performing occupational duties during a work shift. The worker wearsthe sampling train (cyclone, pump, tube and sample filter)for the entire shift (bank to bank). In this study, for practicalreasons, no the personal sample was collected (Biffi andBelle, 2003).

The airborne dust concentration is expressed as mass percubic metre (mg/m3) of air and referred to as sample dust


concentration in the air. Using the sampling period, flow rateand mass of sample collected on the filters, the sample concentration is obtained as follows (Du Plessis and Belle,2014):

(mf-mi)Sample concentration(c) = ––––––– ....... eq 1V x t

wherec is the dust concentration measured in mg/m3

mi is the corrected initial filter mass in mgmf is the corrected final filter mass containing dust in mgV is the sample flow rate in m3/minuteT is the sampling time in minutes

If the sampling period is not an 8-hour period, a calculated8-hour time-weighted average dust concentration (TWA-8 h)is obtained as follows:

(c x t)TWA – 8 hconc = –––––– ........... eq 2480wherec is the dust concentration measured in mg/m3

t is the sampling time in minutes

When silica dust concentration is calculated, an adjustmentis made by determining the actual quartz content (% quartz)on the filter by doing, for example, X-ray diffraction analysis.

The correction made is as follows:

TWA – 8 hquartz = TWA – 8 h x % quartz..........eq 3

The concentration is in mg/m3, with the South AfricanOccupational Exposure Limit (OEL) being 0.1 mg/m3 (MineHealth and Safety Act, No. 29 of 1996). Personal exposuremonitoring was conducted on both the day shift and nightshift using gravimetric sampling pumps. A total of 20 personal exposure samples was collected over the 8-week period. Team leaders, winch drivers, stope teams and rockdrill operators were measured and observed during the studyperiod. The areas monitored during the project focused onthe occupations that are mostly deployed in the stoping faces,strike gullies, centre gullies and back area sweepings.

6. FIELD TRIAL RESULTS

The personal sampling determining exposure measurementsfor the rock drill stope operator (RDO), winch operators andthe in-stope crew are shown in Table 2 (van der Bank,2013). The mass concentrations were calculated using equations 1 and 2 and averaged for the number of measurements.

Table 2. Average measured dust concentrations

From Table 2 it is clear that the average respirable dust concentration as determined from personal exposure monitoring results decreased significantly, with the lowestreduction being measured for the stope team workers at78.1% and the highest reduction of 85.3% being measuredat the winch operator.

In previous studies (See Figure 2 above) the winch operatorswere found to be more exposed than other in-stope workers,but these measurements showed that the general stopeworkers and RDOs were more exposed than the winch operators.

The time-weighted average (TWA) quartz corrected exposure measurements for the RDOs, winch operators andin-stope crew are shown in Table 3. The TWA concentrationswere calculated using equation 3 and averaged for thenumber of measurements. The historical average quartz percentage for Beatrix is between 22 - 28% (personal communications, Van der Bank, 2015) but for the projectaverage quartz percentage was between 11 - 18.8%. Thiswas attributed to the fact that mining had just started in theshaft pillar area.

Table 3. Average measured TWA quartz dust concentration

From Table 3 it can be seen that an average reduction ofbetween 72.6 and 85.3% in the TWA quartz concentrationwas achieved during the trial, with the highest reductionbeing achieved for winch operators. The combined averagereduction in the TWA quartz concentration across all occupations was calculated to be 79.2%. When comparingthe different occupations, the in-stope team members arenow the occupation with the highest average exposure.Although this is still well within the current OEL, it is closeto the new proposed OEL of 0.05mg/m3.A summary of additional field observations made during thestudy within the study area is as follows:• Water covers the total face area from a fixed point.

Occupation Before After Exposure reductionconcentration concentration (%)(mg/m3) (mg/m3)

RDO 1.163 0.231 80.1Winch operator 1.358 0.200 85.3Stope team 1.450 0.317 78.1

Figure 6. One of the underground installations at the trial siteat Beatrix Gold Mine

Occupation Before After Exposure reductionconcentration concentration (%)(mg/m3) (mg/m3)

RDO 0.129 0.02 79.8Winch operator 0.249 0.0366 85.3Stope team 0.168 0.046 72.6


REFERENCES

Beatrix Mine Mandatory Code of Practice for the OccupationalHealth Programme on Personal Exposure to AirbornePollutants. Code of Practice drawn up in accordance with therequired guideline by the Department of Mineral Resources,Reference No. DMR 16/3/2/4-A1, issued by the Chief Inspectorof Mines.

Biffi, M. and Belle, B.K. 2003. Quantification of dust generatingsources in gold and platinum mines. SIMRAC (Safety in MinesResearch Committee), Project GAP 802.

Churchyard. G., Pemba, L., Magadla, B., Dekker, K. Vermeijs,M., Ehrlich, R., te Water Naude, J., Myers, J. and White, N.2003. Silicosis prevalence and exposure response relationships in older black mineworkers on a South Africangoldmine. SIMRAC (Safety in Mines Research Committee),Project SIMHEALTH 606.

Du Plessis, J.J.L. and B.K. Belle, 2014. Sampling of airbornedust and diesel particulates. In Du Plessis, J.J.L. (Ed.),Ventilation and Occupational Environment Engineering inMines, 3rd ed., Chapter 14. Johannesburg: Mine VentilationSociety of South Africa.

Du Plessis, J.J.L. and Pienaar, G. 2009. Gold Fields Project 4M.Document management guidance manual. Internal Gold Fieldscontrol document.

Hnizdo, E. & Sluis-Cremer, G. 1993. Risk of silicosis in a cohortof white South African gold miners. American Journal ofIndustrial Medicine, 24: 447-457.

Kemsley, D. K. 2008. Respirable dust and quartz exposure ofrock drill operators in two Free State gold mines. Master’sThesis, University of the Witwatersrand, Johannesburg, SouthAfrica.

Mzisa, D. 2014. The road to zero harm new milestones.Presentation given at the Mine Occupational Health and SafetySummit, 19 November 2014.

Mine Health and Safety Act, No. 29 of 1996. South Africa.

National Institute for Occupational Health, South Africa.Available at:http://www.nioh.ac.za/?page=dust_projects&id=144

Pienaar, G.J. and du Plessis, J.J.L., 2009. Meeting and exceed-ing the occupational hygiene milestones. First Hard Rock Safe¡V Safety Conference, Sun City, Southern African Institute ofMining and Metallurgy.

Stanton, D.W., Belle, B.K., Dekker, J.J. and du Plessis, J.J.L.2006. South African mining industry best practice on the pre-vention of silicosis. Mine Health and Safety Council, Safety inMines Research Advisory Committee.

Van der Bank, M.I. 2013. Beatrix operations case study: In-stopewaterblast. Mining Unit 2, Beatrix Operations, Sibanye Gold,Internal Report.

Van der Bank, M.I. 2015. Beatrix Mining Operations, Personalcommunications.

Van Greuning, D. 2013. Dust control at Beatrix Gold Mine.Presentation given at the Association of Mine ResidentEngineers (AMRE) Safety Seminar, 16 July 2013.

Van Schoor, M. 2014. Terramin, Personal communications.

• There is no need to enter into any unsafe area to waterdown.

• The water spray washes the blasted face, assisting inexposing misfires.

• Induces airflow with a measured air quantity of up to2.5m3/s.

• There is an increased face velocity measured 15m fromthe water-blast of 3.3m/s.

• There is an increased face velocity measured 30m fromthe water-blast of 1.6m/s.

• The measured water flow rate was 0.75l/s or 45l/min.

• No additional watering down was done during the trials.

No compressed air measurements were taken during thestudy. It is the opinion of the authors that it is important tomeasure the compressed air use at different air pressuresand the impact on water use with different water pressuresavailable. This should be done independently as well aswhen both of the feed components will be entering the nozzle at the same time as the usage will be influenced bythe entering pressure of each other. This will greatly assist inestimating the operational cost associated with the implementation of the intervention.

7. CONCLUSION

The Mine Health and Safety Council Milestones includes areduced level 95% of all individual exposure measurementresults to be below the milestone level for respirable crystalline silica of 0.05 mg/m3. For the industry to meet thisexposure level, significant and focused efforts will berequired and alternative dust control methods will have tobe developed and implemented.

In this paper the use of an in-stope water-blast was investigated and the impact on worker exposure was quantified. From the worker dust exposure concentrationsobtained during the control study it is clear that a significantreduction in worker exposure is possible when effective in-stope dust control is implemented.

An average reduction of between 72.6 and 85.3% in theTWA quartz concentration was recorded during the trial.The combined average reduction in the TWA quartz concentration across all occupations was calculated to be79.2%. When comparing the different occupations, the in-stope team members are now the occupation with thehighest average exposure, but this is still well within the current OEL. The reported worker exposures were achievedduring an 8-week trial period.

It was also concluded from the results achieved and thephysical observations made that the application of this technology will be beneficial not only for operational stopes,but also during vamping. It should also significantly reducethe potential exposure of the vamping crews.

It is anticipated that the impact of the large scale use of thistechnology in the future will be reflected in a reductionstope workers exposure levels.


This year's Mine Occupational Health and Safety Council(MHSC) Summit was held on the 18th and 19th of Octoberunder the theme: "Continuation of the MHSC journey toZero Harm: Every mineworker returning from workunharmed every day".

The summit, which included keynote addresses by theHonourable Minister of Mineral Resources, Mr GwedeMantashe, the Honourable Minister of Health, Dr AaronMotsoaledi, the Chairperson of the Parliamentary PortfolioCommittee on Mineral Resources and several representativesfrom Mining Companies, Labour Organizations and theDepartment of Minerals Resources, was attended by sevenhundred and twenty-eight delegates from across theIndustry and stakeholder groups.

In addition to the keynote addresses and discussions, fourteen, well attended breakaway sessions aimed at theprevention of fatalities and injuries, were tasked to defineways forward in these areas of interest and indicate furtherinterventions.

Of interest to our discipline were the sessions dealing withNoise-Induced Hearing Loss, Occupational Lung Disease,Fires and Explosions and the MHSC Levy Model.

During the Gala Dinner held on the evening of the first day,a special ceremony was held to recognise individuals in theIndustry who made significant contributions to the MHSC inthe last twenty years. Three Fellows of the Mine VentilationSociety of South Africa were amongst the recipients of theCertificates of Recognition awarded by the HonourableMinister, Mr Mantashe in appreciation for their commitmentand contribution to the Journey to Zero Harm. The MVSSAFellows are Mr Bruce Doyle (past President), Mr RalphMcIntyre and Mr Vijay Nundlall (past President),

The President, Executive and Council of the MVSSA expresstheir heartfelt congratulations and gratitude to these threestalwarts, all currently members of Council, for their unfailing efforts and participation in the activities of theMVSSA.

Prestigious recognition of MVSSA members
