At higher concentrations, however, these same metals can produce toxic effects. Some chemicals apparently have no safe threshold levels, as in the case of carcinogens. Although this would lead to the conclusion that no exposure to carcinogenic materials should occur, in reality, it is impossible to achieve zero exposure. We come in contact with natural carcinogens daily, such as the sun's ultraviolet rays. Therefore, the only realistic course is to keep carcinogenic exposure to an acceptable risk level.
Thresholds are useful in determining safe levels of laboratory air contaminants.
TLVs have been established for many common laboratory chemicals. A booklet listing TLVs is published annually. TLVs have been found to protect nearly all workers, though the possibility of hypersensitivity always exists. Adequate laboratory ventilation and good employee practices will keep exposure to airborne chemicals well below safe threshold levels. To control exposure to airborne chemicals, consider the factors affecting airborne concentrations.