Quantcast Section IV. PRODUCTS OF COMBUSTION - TM-55-1915-200-SDC0052

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TM 55-1915-200-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.
6-6. CLASS D FIRES. Class D fires are fires involving combustible metals. Magnesium metal is a 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
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.
6-8. FIRE GASES. The term "fire gases" refers to gaseous products of combustion. Most combustible 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
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.
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.)


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