24/01/2011

Evaluation of the Control of Substances Hazardous to Health (COSHH) Essentials model

The Control of Substances Hazardous to Health (COSHH) Essentials model was
evaluated using full-shift exposure measurements of five chemical components in
a mixture [acetone, ethylbenzene, methyl ethyl ketone, toluene, and xylenes] at
a medium-sized plant producing paint materials. Two tasks, batch-making and
bucket-washing, were examined. Varying levels of control were already
established in both tasks and the average exposures of individual chemicals
were considerably lower than the regulatory and advisory 8-h standards. The
average exposure fractions using the additive mixture formula were also less
than unity (batch-making: 0.25, bucket-washing: 0.56) indicating the mixture of
chemicals did not exceed the combined occupational exposure limit (OEL). The p
aper version of the COSHH Essentials model was used to calculate a predicted
exposure range (PER) for each chemical according to different levels of
control. The estimated PERs of the tested chemicals for both tasks did not show
consistent agreement with exposure measurements when the comparison was made
for each control method and this is believed to be because of the considerably
different volatilities of the chemicals. Given the combination of health hazard
and exposure potential components, the COSHH Essentials model recommended a
control approach ‘special advice' for both tasks, based on the potential
reproductive hazard ascribed to toluene. This would not have been the same
conclusion if some other chemical had been substituted (for example styrene,
which has the same threshold limit value as toluene). Nevertheless, it was
special advice, which had led to the combination of hygienic procedures in
place at this plant. The probability of the combined exposure fractions
exceeding unity was 0.0002 for the batch-making task indicating that the
employees performing this task were most likely well protected below the OELs.
Although the employees involved in the bucket-washing task had greater
potential to exceed the threshold limit value of the mixture (P > 1 = 0.2375),
the expected personal exposure after adjusting for the assigned protection
factor for the respirators in use would be considerably lower (P > 1 = 0.0161).
Thus, our findings suggested that the COSHH essentials model worked reasonably
well for the volatile organic chemicals at the plant. However, it was difficult
to override the reproductive hazard even though it was meant to be possible in
principle. Further, it became apparent that an input of existing controls,
which is not possible in the web-based model, may have allowed the model be
more widely applicable. The experience of using the web-based COSHH Essentials
model generated some suggestions to provide a more user-friendly tool to the
model users who do not have expertise in occupational hygiene.

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AplusA-online.de - Source: Annals of Occupational Hygiene