PRINCIPLES OF TOXICOLOGY

• Physical assessment and fit testing of affected employees
• Employee training in proper use and limitations of respirators
• Respirator storage
• Respirator inspection, cleaning and disinfection, and replacement as needed
• Regular inspection and monitoring/surveillance of work area conditions and employee
exposure and stress
• Periodic program evaluation
To effectively administer a comprehensive program requires a substantial amount of time, technical
competence, and money. Some program elements are a major concern, such as respirator fit and medical
evaluation. Respirator manufacturers began producing multiple-size facepieces available and soft
rubber facepieces only in the late 1990s to accommodate the variety of sizes and facial shapes.
Respirators must be fitted to each individual either in quantitative or qualitative tests, which have used
established protocols involving the use of challenge agents such as corn oil or irritant smoke. Finally,
some individuals are unable to wear respirators at all, because of facial shape or a preexisting medical
problem, such as dentures or heart disease. A particularly sticky concern associated with wearing
respirators is that there are no definitive medical tests, which can lead a physician to determine whether
a worker can wear a respirator without suffering adverse health effects.
In spite of all these limitations, respirators have saved many lives. They must be used when other
feasible methods of control have been exhausted. And of course they are basic to emergency response
procedures where there is no time to use other controls, or when one is facing an unknown situation
that requires immediate action.
The same basic principles apply to other forms of personal protection: they all increase the stress
burden on workers, but with proper training, they can form an effective barrier between the toxic
substance and the body. For example, protective clothing can cause heat stress unless employees are
provided with additional breaks and water intake. Face shields can protect the eyes and face from
corrosive substances, but also reduce visibility. Gloves protect the hands, but at the cost of reduced
dexterity. Hardhats and steel-toed shoes provide protection from safety hazards, but also add weight
that the worker must carry around during the workshift.
All forms of personal protection require expert selection. The correct respirator cartridge must be
used for the particular chemical, concentration, and physical state. For example, a dust filter will
provide no protection against gases or vapors. Protective clothing that is not impermeable to the
chemical can actually worsen skin exposure by providing a continuous reservoir of unevaporated liquid
directly in contact with the skin. Guidance in the selection of appropriate protective equipment may
be available on the MSDSs. Other sources include the NIOSH Pocket Guide to Chemical Hazards and
Guidelines for the Selection of Chemical Protective Clothing.
Summary of Control Technologies In any given situation, it is unlikely that any single specific
control technique will prevent exposures to toxic substances. The challenge in occupational hygiene
is to arrive at a logical blend of all the alternatives outlined above to provide a workplace free of
recognized health hazards and at least a good head start on those occupational health hazards we have
yet to discover.
22.4 CASE STUDIES
Herbicide Application in the Forest
22.4 CASE STUDIES 541
The first case study involves the exposure of herbicide applicators in the management of forests. This
example demonstrates the bridge between industrial hygiene and toxicology. It also demonstrates that