Exposure to chemical substances of many kinds and at many categories of workplaces has become a common situation of societal life and is a global phenomenon. Whether it causes short-term or chronic harm to us depends on the quantity, duration, and frequency of exposure and the toxicity, as well as the sensitivity of the individual. The amount may be minute, but some chemicals accumulate in the body over long periods. Some hazardous chemicals have been known to cause delayed and deleterious effects many years after the exposure. Although the duration and period of exposure may be short, exposure may occur frequently and in excessive concentrations. Children, the aged, pregnant women, and those weakened by disease may be more susceptible than a healthy adult.