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 TM 55-1905-223-SDC
C02 is most suitable for combating Class B and Class C fires; however, its smothering action is a temporary
one and because little cooling is accomplished, the firefighter must remember that the fire will rekindle if the
oxygen is supplied again in the presence of an ignition source. C02 extinguishers have an effective range of
about 3 to 5 feet.
c. Dry potassium bicarbonate chemical (PKP). Dry potassium bicarbonate chemical, usually called
PKP (Purple K Powder), is nontoxic, noncorrosive, and nonabrasive. It can be used effectively on Class B
fires and is four times more effective than equal weights of C02 in extinguishing flammable liquid fire. Dry
chemical is also effective on Class C fires. Smothering and heat radiation shielding contribute to the
extinguishing efficiency of potassium bicarbonate; although the exact mechanism is not known, studies
suggest that a chain breaking reaction in the flame may be the principal cause of extinguishment. Potassium
bicarbonate has little effect on lowering the temperature of the burning material below the ignition point;
therefore, repeated applications may be necessary to prevent reflash PKP is the most effective hand held
extinguisher in combating an oil spray fire. The effective range of this agent is 13 to 22 feet in comparison to 3
to 5 feet for C02 type extinguishers. Potassium bicarbonate also covers a much larger area; however, this
agent leaves behind a residue while the other agents do not. Long discharges will reduce visibility and render
breathing difficult. When approaching a fire, a quick squeeze on the nozzle grip will give some assurance that
the chemical is not caked and will also knock down some smoke. If two PKP extinguishers are spent and little
or no progress is made in extinguishing the fire, the firefighter should proceed to use low-velocity fog.
d. Aqueous film forming foam (AFFF). Aqueous Film Forming Foam, more often called AFFF, is a
6% solution of fluorinated surfactant (detergent) in 94% water. It is nontoxic but highly detergent. It is intended
for use on Class B and Class A fires. The extinguishing action of AFFF stems from its ability to make water
float on liquid fuels which are lighter than water. As the AFFF is discharged and the agent covers the fuel, the
aqueous film floats over the fuel surface and provides a vapor seal. The LCU's foam system consists of a 695
gallon foam concentrate tank and two foam proportioners located in the machinery space between Frames 26
and 28 just inboard of the starboard bulkhead. The proportioners and activated locally in the machinery
space. Once activated, the entire fire main is supplied with foam, including the fire monitors.
Section VII. PORTABLE FIRE EXTINGUISHERS
GENERAL. Most fires are small at origin and in the typical ship are rapidly discovered. They can
6-15.
be easily extinguished if the appropriate application method, proper type, and amount of extinguishing agent
are readily available and promptly applied.
Section VIII. OPERATION OF FIRE EXTINGUISHERS
C02 EXTINGUISHERS. C02 extinguishers are most effective when used at a distance of 5 feet or
6-16.
less from the outer tip of the horn to the edge of the fire. When using C02 extinguishers, the firefighter should
get as close to the fire as possible for maximum effectiveness and should fight the fire until
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