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 TM 55-1905-223-SDC
6-5.
CLASS C FIRES. Class C fires are fires in energized electrical equipment. These fires have
occurred due to shorts, arcing or sparks associated with loose connections, deteriorated wiring, oil-soaked
wiring, and negligence in maintenance of electrical equipment. When the affected equipment is completely
deenergized, the fire becomes either Class A or Class B.
CLASS D FIRES. Class D fires are fires involving combustible metals. Magnesium metal is a
6-6.
combustible (Class D) fuel aboard ship when it becomes heated to a high temperature. This fuel burns with a
dazzling white flame of very high temperature. At this temperature it reacts chemically in the white flame area
with ordinary extinguishing agents such as water, and special methods have been devised to cope with it. In
general, magnesium metal fires are extinguished only by smothering with dry sand, by a cooling action using
large amounts of water from a safe distance, or by spraying water on the unburned metal behind the flame so
that its temperature is lowered and burning can no longer continue.
Section IV. PRODUCTS OF COMBUSTION
6-7.
GENERAL. The products of combustion are fire gases, flame, heat, and smoke. These products
have a variety of physiological effects on humans, the most important being burns and the toxic effects which
result from the inhalation of heated air gases.
FIRE GASES. The term "fire gases" refers to gaseous products of combustion. Most combustible
6-8.
materials contain carbon, which produces dangerous carbon monoxide when the air supply is poor. Unless
the fuel and air are premixed, the air supply in the combustion zone is usually poor. When materials burn,
numerous other gases are formed, such as hydrogen sulfide, sulfur dioxide, ammonia, hydrogen cyanide,
phosgene, hydrocarbons, and hydrogen chloride. Gases formed by a fire depend on many variables,
principally the chemical composition of the burning material, the amount of oxygen available for combustion,
and the temperatures.
Several variables determine whether the gaseous products of combustion will have a toxic effect
on an individual, including concentration of gases in the air, the time of exposure, type of activity, and the
physical condition of the individual.
The toxic effects on persons inhaling fire gases are greater during a fire because the rate of
respiration is increased by exertion, heat, and an excess of carbon dioxide. The primary cause of loss of life in
fire deaths is inhalation of heated, toxic, and oxygen-deficient fire gases.
a. Carbon monoxide is not the most toxic of fire gases but is always one of the most abundant.
In a confined smoldering fire, the percentage of carbon monoxide is usually greater than in a well-ventilated,
brightly burning fire. (See FIGURE 6-1.)
b. Ammonia is formed when acrylic plastic or phenolic and melamine resins are burned.
Exposure to 0.25 to 0.65% ammonia gas for one-half hour can cause death. Hydrogen Flouride (HF) is highly
toxic and is formed when FM-200 agent is exposed to flames or temperatures.
c. Hydrogen Flouride (HF) is highly toxic and is formed when FM-200 agent is exposed to
flames or temperatures over 130 degrees F (700 degrees C). HF gas at levels greater than 3 PPM presents
a hazard to personnel. It is corrosive and irritating to the eyes, skin, mucous membranes, inhilation and can
cause death.
6-2 Change 1
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