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Equations for calculating exposure management objectives for single shift, long-term average, and dual exposure limits.

Hewett D
American Industrial Hygiene Conference and Exposition, June 1-6, 2002, San Diego, California. Fairfax, VA: American Industrial Hygiene Association, 2002 Jun; :52
The majority of exposure limits for gases, vapors, and particulates have as their implicit or explicit goal the control of exposures for each employee. A measure of noncompliance for a typical single shift, TWA exposure limit (or for a 'long-term average' exposure limit) is the probability that a randomly selected worker has a 95th percentile exposure (or mean exposure) greater than the single shift limit (or long-term average limit). The goal of an exposure management program should be to ensure that this probability is small, say 0.05 or less. One method for determining if this goal has been achieved is to directly estimate the probability of noncompliance through the application of resource intensive, repeat sampling of randomly selected workers, followed by components-of-variance analysis. Equations will be presented for calculating site specific exposure management objectives, that if met will help ensure that the exposure management goal is achieved. These equations were derived from a statistical model (which will be briefly discussed) designed to be applied to both conventional, single-shift TWA exposure limits and the less common 'long- term average' exposure limits. The objectives include a target group exceedance fraction, an alternative single shift limit, a target group geometric mean, and a target group mean. Each of these objectives can be evaluated using off-the-shelf sampling strategies, tolerable sample sizes, and robust data analysis procedures. If the site-specific control objective is met, the overall goal of exposure control for at least 95% of the employees is likewise achieved. Examples will be presented for single shift exposures limits, 'long-term average' exposure limits, and for dual limits, where both a single shift and 'long-term average' limit apply.
Exposure-levels; Exposure-limits; Gases; Vapors; Particulate-dust; Particulates; Workers; Sampling
Publication Date
Document Type
Fiscal Year
NIOSH Division
Priority Area
Research Tools and Approaches: Exposure Assessment Methods
Source Name
American Industrial Hygiene Conference and Exposition, June 1-6, 2002, San Diego, California
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division