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362 CHAPTER 6 TARGET LEVELS

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6.2 OCCUPATIONAL EXPOSURE LIMIT VALUES

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 magni-
tude 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 ac-
tivity, 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 re-
main 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.