(1) Gases. A gas is a fluid that has neither independent shape nor volume,
but tends to expand indefinitely. Some examples are air, oxygen, chlorine, and the gas,
which constitutes one of the most serious occupational hazards, carbon monoxide.
(2) Liquids (liquid itself, vapors, and mists). Liquids are fluids characterized
by particles that move freely, without a tendency to separate from one another as in the
case with a gas. Examples of liquids are water and most insecticide formulations.
(a) Vapors. Vapors are gaseous forms of substances that are normally
liquid or solids at normal temperature and pressure. Vapors can be changed to liquids
and solids by increasing the pressure or decreasing the temperature. Among the
vapors, the solvents are particularly hazardous, since they tend to vaporize easily and
contaminate the work atmosphere. Benzyl, carbon tetrachloride, and trichloroethylene
are examples of organic solvents that vaporize readily.
(b) Mists. Mists are airborne droplets formed by the breaking up of a
liquid, as by splashing, foaming, or atomizing. Mist particles can also result from vapor
condensation and are generally larger than vapor particles. Mists are particularly apt to
form over hot solutions and can spread throughout an area if ventilation is poor. Acid
mists are primarily respiratory irritants; however, chromic acid mists are suspected of
causing lung cancer.
(a) Dusts are finely divided solid particles formed by the crushing,
grinding, or abrading of solid materials. Dusts settle to the ground at variable rates
depending on their size and mass. Dusts may cause pneumoconiosis (a chronic
inflammation of the lungs after continued inhalation of dusts after a period of time). The
most common reaction is fibrosis. Silicosis is the predominant form of fibrosis that is
known to cause disability. Systemic poisons in the form of dusts are common, and
some need not be inhaled to cause damage. Skin absorption may be the route of entry
for some toxic dusts. Examples of toxic dusts are those formed from lead, antimony,
(b) Fumes are very small-suspended solid particles generated by
condensation from the gaseous state usually evolved from heated metals or other
materials to form metallic oxides. Fumes are responsible for a particular occupational
illness known as "metal fume fever." "Metal fume fever" is a temporary condition
resembling an acute respiratory infection and occurs most commonly in galvanizing and
welding operations. Some of the metal fumes may be absorbed into the bloodstream
and thereby cause toxic symptoms in other parts of the body. Examples of toxic fumes
are those of lead, mercury, manganese, and cadmium.