Occupational exposure limits
For most toxic substances, there is a close relationship between the amount of the substance absorbed by the body and its effects on health. By knowing this uptake-effect relationship, it is possible to evaluate the risk of exposure. This knowledge can be used to establish a safe limit of occupational exposure. This is called an exposure limit.
Below the exposure limit, there should be no health hazard for the average worker and no deterioration in the degree of comfort that is required to maintain production and to keep the risk of accidents to a minimum. The limit may, however, be expressed by different definitions. The legal status of exposure limits varies from country to country. Though the limit values are based on medical data, they are normally a compromise between different interests. Some countries establish the values as legal standards.
In practice every occupation in industry is exposed to some kind of chemical risk to health. Exposure to several kinds of risks is quite common. Sometimes different substances combine or reinforce one another.
The lower the exposure limit of a substance, the more dangerous it is usually considered to be. The limit values of some substances have been lowered based on new research results showing disorders and even cancer. Workplace monitoring is carried out by measuring the concentration of a certain substance in the air and determining whether it exceeds the limit. Certain substances cause irritation which result in coughing, running eyes or difficulty in breathing; others cause a general feeling of sickness. The majority of substances do not give such warning signals, and can therefore cause fatal injuries and diseases without anybody being aware of it. Measurements to ensure that the limits are not exceeded is the only way of preventing injury and illness.
When assessing the risk to health of a substance we should also remember that heavy work requires considerably more oxygen, i.e. air, than light work. This means that one potentially breathes in considerably more of the substance involved in heavy work than in light work.