APIL Asbestos Conference Exposure from the Engineer’s Viewpoint Quantifying the Dose – how fleeting? Proximity, date and type Engineering issues arising

APIL Asbestos Conference

Exposure from the Engineer’s ViewpointQuantifying the Dose – how fleeting?

Proximity, date and typeEngineering issues arising from Asmussen v Filtrona and

Williams v University of Birmingham

Friday 21 September 2012

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Concentrations, exposures and doses – what does it all mean?

Low dose cases post Asmussen and Williams

A confusing array of terms …

• Dust concentration• Exposure • Dose • ‘A substantial quantity of dust’

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Dust concentration

• The amount of dust (or fibre) in the air• Units:– fibres/ml = fibres/cm3 = fibres/cc– Particles per cc

• Where/how was the measurement made:– Area test– Personal sample

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Dust exposure

• A measure of dust inhaled over a period of time, therefore …

• The average dust concentration in a person’s breathing zone over a period of time

• ‘Time weighted average’(TWA)

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Dust exposure - example

• A personal air sample records an average dust concentration for a task of 2 fibres/ml

• The person carries out the task for 2 hours (and then works in a dust free place for the remainder of the day)

• The person’s exposure will be:– 0.5 fibres/ml 8 hr TWA (2 hrs/8 hrs x 2 fibres/ml)

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What’s the significance?

• Standards are generally expressed as dust concentrations eg TDN 13 triggers Regulations when the average concentration of chrysotile or amosite over any 4 hour period is greater than 2 fibres/ml

• Exposure is required to calculate the dose (ie the total amount of dust to which a person has been exposed)

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Dose estimates

• Estimate of the total dust exposure over a period eg:– Over a working life– With a particular employer

• Required for:– Divisible diseases re causation– Apportionment

• Due to uncertainties will be indicative of the order of exposure, not absolute

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Dose estimates -units

• Typically:Dose (fibres/ml years) = (8 hour time weighted) exposure (fibres/ml) x (working) years of exposure

• Other units can be used eg– fibres/ml days– fibres/ml months

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Some examples

• 1 year @ 1 f/ml = 1 fibre/ml year• 25 years @ 1 f/ml = 25 fibre/ml years• 1 year @ 25 fibre/ml = 25 fibre/ml years

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Quantifying daily exposure

• Object is to estimate the average exposure concentration over an 8 hour shift (the 8 hour time weighted average (TWA))

• If exposure concentration is constant and the shift is 8 hours long then the 8 hour TWA exposure is the same as the exposure concentration.

• If not then:8 hour TWA (f/ml) = (C1T1 + C2T2 + … CNTN)/480

Where: C = the exposure concentration and T = the exposure duration in minutes for each period

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Example

• A person works at task A with exposure of 2 fibres/ml for 6 hours and task B with exposure of 4 fibres/ml for 2 hours.

• 8 hour TWA = (2 x 6)/8 + (4 x 2)/8= 2.5 fibres/ml 8 hour TWA

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‘a substantial quantity of dust’

• Factories Act 1937 and 1961• Not defined, no decided cases– Visible dust cloud, particularly if– Concentration greater than 10 – 12 fibres/ml

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Low dose cases

• Exposure is significant (in the context of causation) if it is: “above a level commonly found in the air in buildings and the general outdoor environment”ie above ‘background level’ which is of the order of 0.000001 – 0.0001 f/ml

• As cited, this is a concentration, not a daily exposure or a dose• Suggests dose may not be an issue in non divisible disease?

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What about short term exposure?

• Consider a person present for 5 minutes in an area where the concentration of asbestos dust is 0.001 fibres/ml as a result of dust originating from lagging in poor condition.

• The concentration is above background, so …• The exposure is ‘significant’.• (subject to foreseeability of risk) a duty holder

could be criticised in the above circumstances, BUT• Would it be causative? (a matter for the medics)

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Thermal insulation (lagging)

• 15 – 100% asbestos• Used up to the late 1960s /

early 1970s• All types of asbestos used• Mixed on site / pre-formed• Also includes rope, string,

yarn, mattresses and blankets

Image source – HSE

Proximity, Date and Type?

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Sprayed Coatings

• Up to 85% asbestos• Usually crocidolite (up to

1970)• Amosite and chrysotile up to

the cessation of use in 1974



18Image source – HSE

Asbestos Insulation Board (AIB)

• 16 – 40% asbestos (mainly amosite)

• Used from 1950s to circa 1980• Numerous construction uses• Fire protection• Heat resistance• Partitions• Some ceiling tiles• General building board


19Image source – HSE

Asbestos Cement (AC)

• 10 - 15% asbestos (chrysotile)• Early 20th Century to 1990s• Numerous construction uses• Corrugated and flat sheets• Moulded products


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Friction products

• Up to 50% asbestos (chrysotile) (as supplied)

• Majority converted to forsterite in use

• Use up to the mid-1980s• Brake and clutch linings



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Other products include (but not limited to):

• Millboard• Fire blankets, gloves, protective clothing• Flooring materials• Textured coatings


Liability in low dose cases

• Two issues:– Foreseeability– ‘Standards of the day’

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Asmussen v FiltronaForeseeability

“Even by [1972] the dire consequences of exposure to small quantities of asbestos was not generally recognised … foreseeability of injury is to be tested against the standard of the well informed employer who keeps abreast of the developing knowledge and applies his understanding without delay” (judgement paragraph 55)

• Implications regarding foreseeability?

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Foreseeable risk

• 1965 ‘Sunday Times’ article, but … • What exposure specific advice was available?– Guidance Literature?– HMFI?

• In some instances long standing knowledge (eg manufacturing, application/removal of lagging)

• In others less clear cut (eg presence of lagging, brake servicing)

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Asmussen v FiltronaStandards of the day

“Safety was to be judged according to the general knowledge and standards of the time.The best indication of the state of knowledge and standards of the time was … Technical Data Note 13. In the light of this guidance, an employer could properly infer that the Factory Inspectorate was indicating at what levels exposure to asbestos fibres was liable to cause danger… the Court was bound to apply the standards of the time” (paragraphs 66 – 67)

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Asmussen v FiltronaStandards of the day

Also reference to Baker v Quantum Clothing:“… statutory duties which refer to safety, injury and danger must … be judged according to the general knowledge and standards of the times”(my emphasis)Paragraph 69

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‘Standards of the time’

• 1937 – 1970: Factories Act ‘any substantial’ or ‘likely to be injurious’ dust

• 1960: American Threshold Limit Values (177 ppcc, arguably 5 - 30 fibres/ml effectively as an 8 hour TWA)

• 1970: TDN 13 (0.2 fibres/ml crocidolite; 2 fibres/ml other, 10 minute and 4 hour reference periods, subject to 12 fibres/ml maximum

• 1976: EH 10 similar to TDN 13 but qualified:“Exposure to all forms of asbestos dust should be reduced to the minimum that is reasonably practicable”

• 1983 on: various revisions to TDN/EH10 standards

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‘General Knowledge … of the time’

• HMFI annual reports• Guidance documents– DOE (Dust and fumes in factory atmospheres)– Asbestosis Research Council (ARC)– Asbestos Information Committee (AIC) (?)– HM Factory Inspectorate

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The implications

• Asmussen v Filtrona seems to me to support an argument that:– Risk must be foreseeable, and – Exposure below ‘the standards of the time’ will be

acceptable • Now supported by Williams v University of

Birmingham

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Williams v University of Birmingham

• Based on exposure, was there a risk that Mr Williams would contract mesothelioma, five steps:– ‘Actual level of exposure’– Knowledge in relation to that degree of exposure– Was it reasonably foreseeable that injury would

occur– What steps should have been taken– Were the steps actually taken

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• Identify the hazard (asbestos dust) and be aware of potential need for precautions

• Consider the risk (possibility of fatal injury with no known safe level of exposure)

• Consider the precautions (by reference to knowledge of the day)

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Compare this to practice

Some observations • Should the first consideration be the level of exposure? • There is (and was) no known safe level of exposure to asbestos dust• The risk under consideration is death (v NIHL in Baker)• The pre 1970 standard was to reduce exposure ‘as far as practicable’ – could

the intention of TDN13 have been to dilute this standard? • For other dusts (not associated with such serious risk) the standard

remained to reduce exposure ‘as far as (reasonably) practicable’ – was the intention a less onerous standard for a more dangerous dust?

• The TDN 13 standards were based on perceived risk of asbestosis NOT mesothelioma.

• The asbestos industry were consulted in the standard setting process and therefore could be argued to have influenced the standards (interesting comments of Lord Dyson at paragraph 101 of Baker v Quantum – standards can be compromised by lobbying)

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Low dose cases: Conclusions

• Each case on its merits• Liability may not necessary follow from

‘significant’ exposure post 1965• Carefully consider exposure AND:– Whether or not a risk was foreseeable– What the duty holder could reasonably be

expected to do about the exposure

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John RaperConsultant Forensic ScientistPragma Asbestos Ltd2 Beacon WalkGringley on the HillDoncasterDN10 4TD

[email protected]

www.pragmaconsulting.net

(01777) 816506

Documents

APIL Asbestos Conference Exposure from the Engineer’s Viewpoint Quantifying the Dose – how fleeting? Proximity, date and type Engineering issues arising