Page 379 - Industrial Ventilation Design Guidebook

334 CHAPTER 5 PHYSIOLOGICAL AND TOXICOLOGICAL CONSIDERATIONS

dustrialized countries, whereas food additives or pesticide residues are not
causes of concern. Nonetheless alcohol use is considered a minor risk com-
pared to the nonsignificant effect of food additives or pesticide residues.
Similarly with occupational health risks, exposure to chemicals in industrial-
ized countries is in most cases a minute hazard when compared to lifestyle
factors. This does not mean, however, that one should not always strive to
prevent industrial exposures and accidents at all times. Perception of risks is
important because it ultimately determines how effectively the knowledge
produced by toxicological research can be utilized in the protection of hu-
man health in the occupational setting and the general environment.
5.3.6.4 Special Considerations
After the use of a chemical becomes widespread, new deleterious effects
on human health may be observed. In such situations, the occupational limit
values will have to be modified. Usually the OELS tend to decrease when more
52
information on the toxicity of a chemical is obtained. Knowledge of the spe-
cific features of various chemicals is thus extremely important for planning
ventilation of industrial premises. It is important to be especially aware of
those chemicals that may cause long-term effects without causing any acute ef-
fects. There are also compounds such as isocyanates that are extremely irritat-
ing at concentrations as low as 0.5 ppm. However, some workers may become
sensitized to isothiocyanates at a concentration of 10 ppb, and therefore this
has to be taken into consideration when planning the industrial ventilation.
Thus, one has to plan against compounds that can cause serious health effects
at concentrations at which their presence cannot be observed by the human
senses, i.e., irritation or odor.
Ultimately, the final stage of risk assessment, risk characterization, aims at
achieving a synthesis from data gathered in steps 1-3. The goal of such a synthe-
sis is, in addition to qualitative risk assessment, quantitative risk assessment.
This implies that the outcome of the process should be numerical, e.g., a num-
ber or other estimate which indicates how many extra cases of a deleterious
health outcome are produced due to exposure to a given exposure level in a
49
given population. Decisionmakers demand that toxicologists be able to come
up with a reliable estimate of the relative importance in terms of severity of the
health outcome or the number of new cases of disease. This would then allow
them to prioritize the health hazards, and also carry out the kinds of expense/
benefit analysis usually utilized in these situations. It would then be easier to
make decisions on which chemical problems to tackle first, and at which con-
centration level the occupational limit value of a given chemical should be set.
These measures are important for the preventive measures to be undertaken.
An important issue in the toxicity of chemicals and in assessing their risks is
the inherent toxicity of a chemical. This implies the potency, i.e., the magnitude of
the dose, at which the chemical can induce a toxic effect, whether cancer, liver
damage, or nervous dysfunction. One example of a characteristic of a chemical is
its reactivity, which may markedly affect its potential to cause allergic reactions or
cancer or to induce irritation of the respiratory tract. Thus, detailed information
on the characteristics of a compound is of major significance in understanding the
mechanisms of the effects that it can induce in humans and in other living organ-
isms and in understanding the effects themselves. 87