Basic Concepts for Maximum Allowable Concentrations of Toxic Substances

Exact definition of basic concepts and terms is of paramount importance to the question of maximal allowable concentrations of toxic substances in industrial atmospheres. The differences existing in various countries are often due to differences in the interpretation of basic concepts. Mutual agreement on the question of basic concepts will facilitate a rapprochement of points of view, and, perhaps, even an agreement on specific problems and individual standards. The term maximal allowable concentration, (M.A.C.), should be used to denote such concentrations of various harmful chemical substances in the form of gases, vapours and dusts in industrial atmospheres, which, by their constant effect on workers during normal daily work over an indefinite period of time, can produce no pathological change or disease detectable by current methods of examination. M.A.C.'s, therefore, can produce neither acute, nor chronic occupational poisoning. The establishment of M.A.C.'s of toxic substances and the design of preventive measures against occupational poisoning under actual conditions must have regard to the possibility of penetration of toxic substances not only through the respiratory tract, but also through the skin and through the digestive organs. However, the respiratory tract is most important. Therefore the main preventive measure against occupational disease will be the avoidance of contamination of atmospheres with toxic substances, and the effort to preserve the highest possible cleanness of air in industrial plants is fully justified. The establishment ofM.A.C.'s as a fundamental element in legal provisions concerning occupational hygiene (which provisions are obligatory for all industrial institutions) pursues the humane aim of complete protection of the health of labourers working for many years in industrial plants. The establishment ofM.A.C.'s is intended for: (a) organizations and persons designing technological processes and production facilities, in order that these facilities may secure minimal escape of toxic substances into factory atmospheres; (b) calculating air exchange when designing ventilating systems for plants where toxic gases and vapours arise; (c) the medical inspection of the condition of the atmosphere in workrooms. In our opinion, the M.A.C.'s of toxic substances should not serve only for the narrow purpose of medical inspection of factory atmospheres, but should also become a primary governing factor in the design of technological