Hazards of Chemicals and Gases
Hazard is the possibility that a material will cause injury when a specific quantity is used under
specific conditions. Several key elements are considered when evaluating a health hazard.
Toxicity of the materials used
Physical properties of these materials
Absorption probabilities of these materials by individuals
Extent and intensity of exposure to these materials
Control measures used
Toxicity is relative. It refers to a harmful effect on some biologic mechanism. The term toxicity
is commonly used in comparing one chemical agent with another, but such comparison is
meaningless if the biologic mechanism, and the conditions under which the harmful effects
occur, are not specified.
Although the toxic effects of many chemical agents used in industry are well known, the toxic
effects of many other commonly used chemical agents are not as well defined. The toxicity of
a material is not a physical constant (such as boiling point, melting point, or temperature);
therefore, only a general statement can be made concerning the harmful nature of a given
Many chemical agents are nonselective in their action on tissue or cells; they may exert a
harmful effect on all living matter. Other chemical agents may act only on specific cells.
Another agent may be harmful only to certain species; other species may have built-in protective
The degree to which a substance will affect living cells can be measured only after recognizable
changes have occurred following absorption. Some changes (impaired judgment, delayed
reaction time) may be produced at levels too low to cause actual cell damage. Toxicity is
dependent upon the dose, rate, method, and site of absorption, and many other factors including
general state of health, individual differences, tolerance, diet, and temperature.
In general, industrial poisonings usually result from inhalation, ingestion, and absorption.
The inhalation and absorption of toxic agents by the lungs is dependent upon the
solubility in body fluids, the diffusion through the lungs, the volume of
inhalation, the volume of blood in the lungs, and the concentration gradient of
vapors between the inhaled air and the blood.
Ingestion of the toxic agent can occur to some extent; however, there would
generally be considerable inhalation of the material where such conditions exist.