Hazards of Chemicals and Gases
Absorption through the skin can occur upon exposure to some toxic agents.
Some liquids and vapors are known to pass through the skin in concentrations
high enough such that respiratory protection is not adequate. For example,
hydrogen cyanide (HCN) is known to pass through the unbroken skin.
Consideration should be given to the type of work clothes being worn; if they
become saturated with solvents, they will act as a reservoir to bathe the body
continually with the harmful material.
Most volatile (easily vaporized) organic compounds are eliminated from the body in a matter
of hours or, at most, days. Many of the poisonous elements, however, can be stored for long
periods of time in various parts of the body. Chronic (long term) toxicity damage is unlikely
to have an even distribution throughout the body. In toxicity studies with radioactive isotopes,
the organ which suffers the most severe damage and appears to contribute most to the toxic
effect on the body as a whole, is called the critical organ. The particular organ that shows the
largest amount of damage is the one that is chosen for estimating the effect.
Industrial poisoning may be classified as either acute or chronic. The classification is based on
the rate of intake of harmful materials, rate of onset of symptoms, and the duration of
Acute poisoning is characterized by rapid absorption of the material and sudden, severe
exposure. For example, inhaling high levels of carbon monoxide or swallowing a large quantity
of cyanide compound will produce acute poisoning. Generally, acute poisoning results from
a single dose which is rapidly absorbed and damages one or more of the vital physiological
processes. The development of cancer long after recovery from acute radiation damage is
called a delayed acute effect.
Chronic poisoning is characterized by absorption of a harmful material in small doses over a
long period of time; each dose, if taken alone, would barely be effective. In chronic poisoning,
the harmful materials remain in the tissues, continually injuring a body process. The symptoms
in chronic poisoning are usually different from the symptoms seen in acute poisoning by the
same toxic agent.
The Occupational Safety and Health Act of 1970 requires that the Health and Human Services
publish at least annually, a list of all known toxic substances by generic family, or other useful
grouping, and the concentrations at which such toxicity is known to occur. Under the OSHA
Act, the Secretary of Labor must issue regulations requiring employers to monitor employee
exposure to toxic materials and to keep records of any such exposure.
The purpose of The Toxic Substances List is to identify "all known toxic substances" in
accordance with definitions that may be used by all sections of our society to describe toxicity.
An excerpt of this list is illustrated in Figure 1. It must be emphatically stated that the presence
of a substance on the list does not automatically mean that it is to be avoided. A listing does
mean, however, that the substance has the documented potential of being hazardous if misused,
and, therefore, care must be exercised to prevent tragic consequences.