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INTRODUCTION
This report deals with current understanding of
combustion-product toxicity and fire hazard assessment.
In studying these issues, the Committee on Fire Toxicology
examined the number of fire-related deaths in the United
States and possible causes of these fatalities. A short
primer on fire and fire hazard was developed, to provide
a better understanding of the status of fire hazard
models and test methods. The Committee has studied the
hazards associated with fires and reviewed the test
methods now used to evaluate the toxicity of combustion
products. Finally, the Committee developed guidelines
for hazard assessment and prepared specific case studies
based on them.
About 5,000 people die every year in the United States
as a result of fire. Technical improvements have
occurred--e.g., in building fire codes, firefighting
techniques, flammability standards for mattresses, the
use of fire detection devices in homes, the use of
sprinkler systems in public buildings, and public fire-
safety awareness--and the annual number of fire deaths
has been decreasing for 20 years. But it is commonly
believed that the fire death rate might have decreased
even more if new materials of synthetic origin had not
come into use.
Most fire-related deaths are due to inhalation of
toxic gases in smoke, not to fire or heat itself. Carbon
monoxide (CO) is thought to be the most common cause of
fire-related death. Because of its high affinity for
hemoglobin, relatively small concentrations of CO can
saturate the blood, form carboxyhemoglobin (COHb), and
deprive tissues of oxygenation. In general, COHb
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concentrations above about 30-40% seriously impair the
ability of humans or animals to perform a task, and
concentrations above 50-60% can be fatal. Some people
can function even at COHb concentrations up to 50%,
because a hypoxia challenge, whether caused by oxygen
(O2) depletion or CO accumulation, increases cerebral
blood flow. In the face of decreasing O2 availability,
however, this compensatory mechanism eventually fails to
deliver enough O2 to the brain, and the victim loses
consciousness. If the victim survives, severe necrologic
disorders can sometimes be seen after a period of apparent
recovery. It was recently suggested that hydrogen cyanide
(HCN) can also contribute importantly to the overall toxic
hazard of fire. The neuropathologic patterns after HCN
and CO exposure appear to be similar; thus, despite the
difference in mechanisms of inducing hypoxia, the two
gases might damage neural tissue in an identical manner.
In addition to toxic gases, fire generates many
respiratory irritants--such as hydrogen chloride, acro-
lein, and sulfur dioxide--that can cause necrosis and
pulmonary edema. Delayed deaths have reportedly occurred
after what appeared to be mild exposures to these gases.
A review of the major combustion products and their indi-
vidual contributions to the toxic hazard affords only
partial insight into the total toxic hazard in fire. The
overall hazard is associated with exposure to mixtures of
the individual combustion products and with their effects
in preventing escape from the fire environment. The
irritant effects of fires on survivors can be classified
as early and late. The early effects are usually
associated with damage to the upper airways and the
respiratory tract in general. The most common late
sequela of a single exposure is some degree of pulmonary
obstruction. Studies of firefighters have shown, with
some variability, that a long-term consequence of
repeated fire exposure can be the development of an
obstructive, restrictive, or mixed ventilatory defect.
With regard to the possible increase in cancer incidence
in firefighters, the results of several studies have
suggested higher than normal incidences of a variety of
cancers, but there seems to be no conclusive relationship
between the type of cancer and exposure history.
The roles of the technical improvements in fire
prevention and detection mentioned above in fire safety
and fire loss are not well understood. It is therefore
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not possible to determine whether the use of "new
materials" is associated with different or increased
hazard. However, even in the absence of a demonstrable
increase in the role of toxicity in fires, the concern
over new materials warrants attention. It is appropriate
to continue the deliberate process of developing methods
for analyzing and predicting product response to fire
under expected conditions of use. Such methods will be
useful both for selecting materials for specific uses and
for substantiating regulatory positions.
The hazards presented by fire are best assessed through
consideration of all the characteristics of fire. The
hazard associated with smoke depends both on how rapidly
a material produces smoke and on the toxic and irritant
potency of the smoke once produced. In general, smoke
hazard cannot be characterized unless both kinds of
information--production rate and potency--are taken into
account. Smoke production rate is a function of a
material's fire properties and of the environment in
which the fire takes place. Therefore, hazard depends on
the situation: laboratory measurements of materials them-
selves do not predict hazard until the measured properties
are evaluated in the context of how the material is to be
used and how it might burn--i.e., in a given fire sce-
nario. The two means of providing information on the
fire scenario are full-scale simulations and mathematical
fire models. The expense and cumbersomeness of full-scale
fire simulation make reliance on mathematical models
desirable, and the Committee believes that models have
been developed to the point where they can be used--
cautiously--as a basis for fire hazard assessment.
Representative terms from entire chapter:
toxic hazard
