flammable liquid pumps, and mixers may be
interlocked with the dry chemical system and
arranged to shut down automatically upon
discharge of the system.
Local application systems are arranged to
discharge dry chemical directly on the hazard,
without any enclosure (fig. 8-37). Typical local
application systems are used for the protection of
paint dip tanks and restaurant range hoods.
Ventilating fans, conveyors, flammable liquid
pumps, and mixers may be interlocked to shut
down automatically upon discharge of the system.
Hose line systems discharge dry chemical
through manually operated nozzles connected by
hose or by piping and hose to a fixed supply (fig.
Dry chemical used in approved systems is
mostly sodium bicarbonate, very finely ground,
to which has been added other ingredients to keep
it free flowing and to resist caking. Other agents
used in dry chemical extinguishing systems include
potassium bicarbonate, potassium chloride, and
monoammonium phosphatemultipurpose type.
The dangers dry chemicals used in fire ex-
tinguishing concentrations cause exposed person-
nel are temporary breathing difficulty and reduced
visibility. In areas using total flooding systems,
suitable means should be provided to permit
evacuation of personnel. In areas using local
application systems where the dry chemical is not
confined, there is little hazard to personnel.
Dry chemical systems are used primarily for
extinguishing fires in flammable liquids.
Bicarbonate base dry chemical can be particularly
effective for extinguishing fire in deep fat fryers
caused by overheating. The saponification reac-
tion between the dry chemical and fat or grease
Figure 8-37.Local application dry chemical system
prevents re-ignition by turning the fat to soap.
Multipurpose dry chemical will not react with the
fat or grease and can prevent the saponification
reaction between the fat or grease and any
bicarbonate base dry chemical subsequently used.
Dry chemical systems are not suitable for fires
in materials (such as cellulose nitrate) that con-
tain their own oxygen supply. They are not
normally used for fires involving delicate electrical
equipment such as telephone switchboards, com-
puters, and certain other electronic equipment
because the dry chemical will insulate the fine and
delicate contacts. The contacts will then need
Monoammonium phosphate and potassium
chloride are slightly acidic, and in the presence
of moisture can corrode metals such as steel, cast
iron, aluminum bronze, and titanium. Corrosion
can be minimized by prompt cleanup. Most dry
chemical agents can be cleaned up by wiping,
vacuuming, or washing the exposed materials or
surfaces. Monoammonium phosphate will require
some scraping and washing if exposed surfaces
were hot when the agent was applied.
TYPES OF SYSTEMS
There are basically two types of dry chemical
1. Gas cartridge systems that use a container
of expellant gas that, when released by manual
Figure 8-38.Stored pressure dry chemical cylinder with