Users of occupational exposure limits (OELs) often fail to distinguish between the complementary processes of risk assessment and exposure (risk) management. The former refers to those activities that lead to the selection of a reasonably protective exposure limit and often includes an analysis of exposure databases and an evaluation of group-based risk. The latter focuses on individual risk, and refers to those actions required of employers to ensure that each employee is unlikely to incur harm to health. This presentation focuses on how this failure to distinguish leads to misinterpretation and misuse of OELs. A typical OEL definition consists of at least three components: a concentration, an averaging time, and a target (usually the individual worker). OELs are occasionally improperly applied, resulting in a reduction of the expected level of protection. For example, sampling strategies proposed by the American Industrial Hygiene Association (AIHA) and Comite Europeen de Normalisation (CEN) permit workers to be aggregated into exposure groups. Under certain circumstances this practice can leave some workers unevaluated and unprotected. Protection is also reduced when the averaging time is extended from a single shift to multiple shifts. Frequently, OELs are misinterpreted as upper limits to exposures averaged over weeks, months, or even years, rather than a single shift. Much of this confusion can be traced to the desire of some to reconcile research (epidemiology) sampling strategies with compliance sampling strategies. But the two have fundamentally different goals and objectives. Others are simply attracted to alternative OEL interpretations that permit frequent overexposures (i.e., measurements that exceed the OEL), thus making compliance easier. Given the current limitations of industrial hygiene and occupational epidemiology, and the general unwillingness of employers to routinely collect exposure data, OELs should continue to be defined as upper limits for single shift exposures. The current OEL model, which permits the use of proximate risk management goals to realize long-range objectives, should be retained. There are, however, valid reasons for augmenting this model to include criteria for evaluating compliance with long-range objectives. The augmented OEL model would be applicable to future new and revised OELs. The author suggests that OEL setting organizations consider harmonizing definitions and statistical interpretations for both existing and new OELs, thus minimizing future misinterpretation and misuse.
Paul Hewett, National Institute for Occupational Safety and Health, Division of Respiratory Disease Studies, 1095 Willowdale Road, Morgantown, WV 26505