Section V. FIRE HAZARDS OF MATERIALS
6-13. FIRE HAZARD MATERIALS. Several materials that can support a fire are briefly discussed here.
a. Cable insulation. Most cable insulation contains a large quantity of poly inyl chloride (PVC) which will sustain
combustion at 6800 F when decomposed in a fire. PVC will liberate hydrogen chloride and hydrogen cyanide gases
when heated to about 3900 F. These gases interfere with vision, cause intense respiratory irritation, and may cause
death due to lung edema 12 to 36 hours later. The best way to extinguish this type of fire is to bring water to bear in the
form of water fog. In the interim, Aqueous Film Forming Foam (AFFF) is most effective against this type of fire. If power
to the affected cables is completely deenergized, this type of fire is considered a Class A fire.
b. Diesel fuel. Diesel fuel has a flash point of 140o F and an autoignition (ignition without the assistance of an
external pilot source) temperature of 400o F. When ignited, it will produce a heavy black smoke. The fire should be
attacked using AFFF. If AFFF is not available, use dry chemical extinguishers. Low-velocity water fog should be
available when setting the reflash watch.
c. Hydraulic oil. Hydraulic oil has a flash point of about 400o F and an autoignition temperature of over 650o F. If
hydraulic oil at 3,000 psi is atomized from a leak in a pipe, it will readily burn if exposed to an ignition source. Laboratory
tests indicate that the oil mist fire will continue to burn even if the ignition source is removed when the oil is at the normal
operating temperature of 110 F to 130 F. A hydraulic oil fire can ignite surrounding combustibles such as cable
insulation and produce intense heat once its ignition temperature has been reached. Such a fire will cause a pressure
increase in a sealed compartment. Hydraulic oil spray/mist fires should be attacked with dry chemical fire extinguishers.
AFFF should be used against two-dimensional fires. If the fire is an oil mist, the extinguisher should be aimed at the
base of the fire until the flame is extinguished. This will interrupt the fuel flow to the fire. If the fire cannot be
extinguished by dry chemical extinguishers, water should be brought to bear. Dry chemical extinguishers do not cool a
fire; therefore, reflash can be expected. Low-velocity water fog should be available when setting the reflash watch.
d. Oil mist. If an oil leak mist accumulates before an ignition source is introduced, later ignition can result in an
explosion. It is important to secure and/or depressurize the source of the leak as soon as possible and avoid actions that
could cause an arc, sparking, or open flame before the mist is dispersed.
e. Vegetable oil. The vegetable oil used in cooking has a smoke point of 420 F, a flash point at 10 F to 20 F
higher, and an autoignition temperature of about 600 F when fresh. Respective temperatures are much lower when the
oil has been used. If installed, the aqueous potassium carbonate system should be used to extinguish a