PRINCIPLES OF TOXICOLOGY

524 CONTROLLING OCCUPATIONAL AND ENVIRONMENTAL HEALTH HAZARDS
(1962), and labor unions began to lobby for better protective measures in workplaces. These events
resulted in a number of legislative initiatives at the end of the decade. Along with other environmental
laws, the Occupational Safety and Health Act (OSHA) was passed in 1970. The OSHAct assured that
every employee “has the right to a workplace free of recognized hazards.” Since that time, the field
of industrial hygiene has grown dramatically, both in size and sophistication.
The basic philosophies of industrial hygiene are well-recognized: protection of worker health is a
worthwhile goal; the burden of protecting the worker is primarily the employer’s, but the worker also
has the responsibility to exercise self-protection. The hierarchy of control measures is, in order of
effectiveness, elimination of toxic chemical use, substitution of less toxic material for more toxic
substances, engineering controls, administrative controls, and personal protective equipment. Education
and training of workers is increasingly recognized as a key aspect of industrial hygiene, as
evidenced by the proliferation of “right to know” laws that have swept the country. Essentially, the
idea is that an informed worker is a safer worker; if employees understand why a safety rule has been
established, they are more likely to follow it.
The control of occupational health hazards is dependent on the anticipation of potential health
hazards in new facilities and their recognition in existing facilities. Once the potential health hazards
have been identified, they are evaluated by a process of observation of the work place and work
practices and quantification of the risk associated with the hazard. When these risks reach unacceptable
levels, methods of controlling the exposures must be identified and implemented to minimize the
potential for harm to the worker. The identification and evaluation phases are sometimes referred to
as risk assessment, while the control phase is referred to as risk reduction or risk management.
In practice, the industrial hygienist plays the major role in the risk assessment process. On the other
hand, risk reduction involves many different players with a variety of backgrounds: the supervisors
and workers who know the process and must work with any new equipment or procedures that are
installed; engineers who are familiar with control technologies and understand the production process;
toxicologists who may identify adverse effects from chemical exposure; physicians capable of
designing medical surveillance programs to help identify emerging adverse health effects in individuals;
the industrial hygienist who understands how contaminants behave in both the environment and
the human body and understands when to use the various control strategies; and managers who must
allocate sufficient resources to pay for controls. Each player brings special abilities and knowledge to
the problems associated with minimizing health risk.
As an applied science, industrial hygiene relies on the basic sciences of biology, chemistry, physics,
and statistics, as well as the social sciences—sociology, and political science—to achieve its goals.
22.2 EXPOSURE LIMITS
The bridge between toxicology and industrial hygiene has traditionally been the development of
exposure limits. Exposure limits are reference values that should not be exceeded. They have been
developed to protect the large majority of an exposed population from the development of environmentally
induced diseases. The level of protection varies with the type and severity of the expected
outcome as well as the sensitivity of the exposed population.
Air-Contaminant Exposure Limits
The threshold limit values (TLVs ® ) for chemical substances have been published by the American
Conference of Industrial Hygienists (ACGIH) since 1946 and have increased in number since that
time. Generally, the TLVs ® for many substances have been lowered as the identification of more subtle
adverse health effects has become possible. Mastromatteo (1988) documented the history and progression
of TLVs ® . ACGIH bases the TLVs ® on information gathered by the ACGIH TLV ® Committee
from human experience in the workplace and experimental human and animal studies.