2 fibres/ml - John Raper Consulting

APIL Asbestos Conference
Exposure from the Engineer’s Viewpoint
Quantifying the Dose – how fleeting?
Proximity, date and type
Engineering issues arising from Asmussen v Filtrona and
Williams v University of Birmingham
Friday 21 September 2012
Concentrations, exposures and doses – what does
it all mean?
Low dose cases post Asmussen and Williams
A confusing array of terms …
Dust concentration
‘A substantial quantity of dust’
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
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 weighted average’(TWA)
Dust exposure - example
• A personal air sample records an average
dust concentration for a task of 2
• 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)
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)
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
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
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
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
C = the exposure concentration and
T = the exposure duration in minutes for each period
• 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
‘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
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?
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,
• Would it be causative? (a matter for the medics)
Proximity, Date and Type?
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?
Sprayed Coatings
• Up to 85% asbestos
• Usually crocidolite (up to
• Amosite and chrysotile up to
the cessation of use in 1974
Image source – HSE
Proximity, Date and Type?
Asbestos Insulation Board (AIB)
• 16 – 40% asbestos (mainly
• Used from 1950s to circa 1980
• Numerous construction uses
• Fire protection
• Heat resistance
• Partitions
• Some ceiling tiles
• General building board
Image source – HSE
Proximity, Date and Type?
Asbestos Cement (AC)
• 10 - 15% asbestos (chrysotile)
• Early 20th Century to 1990s
• Numerous construction uses
• Corrugated and flat sheets
• Moulded products
Image source – HSE
Proximity, Date and Type?
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
Image source – HSE
Proximity, Date and Type?
Other products include (but not limited to):
Fire blankets, gloves, protective clothing
Flooring materials
Textured coatings
Liability in low dose cases
• Two issues:
– Foreseeability
– ‘Standards of the day’
Asmussen v Filtrona
“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?
Foreseeable risk
• 1965 ‘Sunday Times’ article, but …
• What exposure specific advice was available?
– Guidance Literature?
• In some instances long standing knowledge
(eg manufacturing, application/removal of
• In others less clear cut (eg presence of lagging,
brake servicing)
Asmussen v Filtrona
Standards 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)
Asmussen v Filtrona
Standards 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
‘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
‘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
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
• Now supported by Williams v University of
Williams v University of Birmingham
• Based on exposure, was there a risk that Mr
Williams would contract mesothelioma, five
– ‘Actual level of exposure’
– Knowledge in relation to that degree of exposure
– Was it reasonably foreseeable that injury would
– What steps should have been taken
– Were the steps actually taken
Compare this to practice
• Identify the hazard (asbestos dust) and
be aware of potential need for
• Consider the risk (possibility of fatal
injury with no known safe level of
• Consider the precautions (by reference to
knowledge of the day)
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
• 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)
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
John Raper
Consultant Forensic Scientist
Pragma Asbestos Ltd
2 Beacon Walk
Gringley on the Hill
DN10 4TD
[email protected]
(01777) 816506

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