An exposure-assessments strategy accounting for within- and between-worker sources of variability.

A strategy is presented for comparing exposures to an occupational exposure limit (OEL) and for suggesting appropriate interventions when exposures are unacceptable. The major departure from previous approaches is the explicit recognition that exposures vary both within and between workers in a given occupational group. The primary goal is to determine whether the probability of overexposure is acceptably small (a value of 0.10 or less is recommended), with overexposure being defined as the likelihood that a randomly selected worker's true mean exposure exceeds the OEL. The exposure-assessment protocol contains five levels. It is suggested that at least two shift-long measurements be randomly collected from each of 10 workers for preliminary analysis. If the logged exposure data appear to be appropriate for testing (Level 1), the probability of overexposure is compared to the pre-determined value via a rigorous test of statistical significance (Level 2). Based upon published data, this test is likely to classify exposures as acceptable with 20 measurements when the group mean exposure is less than one-fifth of the OEL. However, if exposure is found to be unacceptable, re-sampling can be considered to increase the power of the test (Level 3). Otherwise, it is necessary to reduce exposures and then to re-apply the protocol. If it appears that all persons in the group have essentially the same predicted mean exposures (Level 4), then engineering or administrative controls are recommended. If, on the other hand, substantial differences appear to exist amongst these predicted mean values, regrouping and/or modifications of tasks and work practices should be considered (Level 5). Application of the protocol is illustrated with samples of data from four groups of workers exposed to inorganic nickel in the nickel-producing industry.