6.2.1 Introduction

The harmful effects of an environment in which certain chemical agents are present in the air inhaled by employees have been known for a long time. A person may be exposed to many potentially harmful chemical, physical, and biological agents during his or her working life and, depending on the magni­tude of the dose, the result can be disease and even death.

In this chapter we will consider only exposure to chemical agents in the air. We will not address other risks that do not influence the dose received by a worker.

These chemical agents can be any chemical element or compound, on its own or mixed, as it occurs in the natural state or as produced by any work ac­tivity, whether or not produced intentionally, and whether or not it is placed on the market. According to EINECS (European Inventory of Existing Commercial Substances) and the ELINCS (European List of Notified Chemical Substances), the number of such substances, not counting their mixtures or preparations, is well over 150 000. To these single agents we must add mixtures and solutions composed of two or more substances, intermediate substances formed during chemical reactions, and by-products formed during chemical reactions that re­main at the end of the reaction or process. Fortunately, only a few hundred of these chemical substances are used regularly on a commercial basis.

Thus, it can be said that in practically all activities there are risks to health related to the presence of chemical agents. To evaluate their severity we should consider whether the exposure occurs continuously or at irregular intervals, the possible entry routes to the body, the concentration changes with time and place, as well as the aggregation state of the contaminant in liquid, dust, mist, fume, or vapor form.

The mechanisms behind the different types of risks are also quite varied, because manufacturers may apply different conditions and agents, and each manufacturing stage may involve different job functions and therefore differ­ent exposure conditions. Distance to emission sources and physical parame­ters such as rate of release, air currents, and meteorological variations have a profound influence. The variability of exposure conditions is made even greater by work patterns, individual practices, and simultaneous exposure to several substances acting together.

Thus, there is a clear need to establish the relationship between the health effects of hazardous chemical agents in the environment and the level of occu­pational exposure to the body by means of an occupational exposure limit, in which a reference figure for the concentration of a chemical agent is set. In fact, occupational exposure limits (OELs) have been a feature of the industri­alized world since the early 1950s. They were introduced, primarily in the United States, at a time when measures to prevent occupational diseases were considered more beneficial than compensating victims, and in this sense OELs have played an important part in the control of occupational illnesses.

The idea behind OELs is to identify the highest level of exposure concen­tration and the corresponding reference time period for which we can be con­fident that there will be no adverse effects on health. However, the concentrations and lengths of exposure at which the presence of airborne chemical agents could damage health have not been clear for many years, and even today there are many questions to be answered.

Generally, OELs are set in reference to the airborne route such that expo­sure, even when repeated on a regular basis during the working schedule throughout the working life of a normal worker, will not lead to adverse ef­fects on the health of exposed persons or their progeny for any time—short term, long term, or beyond the end of the working life—as far as can be pre­dicted from the state of knowledge.

One problem rnay arise in defining who is a normal worker. This means taking account of the variability in biological response together with the uncertain environmental data. A small percentage of workers may experience discomfort from some substances at concentrations at or below the OEL. Moreover, some may be affected more seriously by the aggrava­tion of preexisting conditions or the development of an occupational ill­ness. Therefore, OELs should not apply to special-risk workers, those who are hypersusceptible or otherwise unusually responsive to industrial chem­icals because of genetic factors, age, personal habits, medication, or previ­ous exposure.

Usually, OELs are stated as the eight-hour time-weighted average concen­tration of exposure to a substance in gaseous, vaporous, or suspended form in the air at the workplace. Later on we will give a more precise formula.

With all this in mind, OELs should be regarded as an important part of the overall approach to ensuring the protection of health in the workplace, providing a criteria by which decisions can be made as to whether the airborne concentra­tion of a given substance is sufficiently low to avoid adverse health effects.

In essence, OELs may be used for a number of purposes, for which the principal objective is to provide standards or criteria against which the results

Of environmental monitoring in existing workplaces may be compared to en­sure that, as far as the current state of knowledge permits, control is adequate to protect health. They may also be used for design purposes, to ensure that new plants and process are engineered in such a way that exposures can be controlled at levels that will not damage health. They should not be used as a basis for assessing the acceptability of nonoccupational exposure, for compar­ing the toxicity of one substance with that of another, in the evaluation or control of community air pollution nuisances, or as proof or disproof of an existing disease or physical condition.