EAS Inc. Technical Reports (no charge)
Hewett, P. (2005): Technical Report 05–03 - Performance-based exposure
assessment strategies for TWA exposure limits. Exposure Assessment Solutions,
Inc. (www.oesh.com).
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ABSTRACT
A procedure is proposed for designing a performance-based "exposure assessment"
strategy; that is, a strategy that is both effective (i.e., the strategy will
reliably achieve a specific objective), and efficient (i.e., the strategy requires
a minimum or tolerable expenditure of program resources). The objective addressed
in this paper is the detection of an unacceptable group exposure profile during
a baseline exposure assessment survey, although the design of a termination/reduction
strategy is addressed. The strategy "performance curve" (i.e., operating
characteristic curve) is used as the primary instrument for comparing the effectiveness
of different strategies. The strategy "sample size" curve, is used
to evaluate the efficiency of the sampling strategy.
Computer simulation was used to estimate the performance and sample size curves
for five off-the-shelf exposure assessment strategies. Two strategies - the
OSHA Inspector strategy and the OSHA-NIOSH strategy (used in the OSHA 6b standards)
- are highly efficient; that is, a decision can be reached on the basis of just
a few measurements. But neither are very effective; they do not have sufficient
power to reliably detect poorly controlled group exposure profiles. Consequently,
neither is suitable for baseline exposure assessments, but with modification
their performance can be improved. The default versions of the AIHA "Similar
Exposure Group" strategy and a similar two-stage corporate strategy are
both effective at detecting poorly controlled exposure profiles. Computer simulation
showed that modest changes in the corporate strategy will result in a substantial
improvement in efficiency, without compromising its effectiveness. Similar changes
could be applied to the AIHA strategy. The fifth strategy was taken from guidance
on exposure assessment published by the European Union. Decisions are made with
great efficiency, but computer simulation revealed that it was not sufficiently
effective. A simple change to the strategy improved the effectiveness without
changing strategy efficiency.
In summary, the author suggests that strategies for baseline exposure assessments
be purposefully designed to reliably detect poorly-controlled exposure profiles.
As demonstrated in this paper, computer simulation can be a valuable tool when
designing true, performance-based exposure assessment strategies.
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