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CLASSES OF FIRE | Up
Airman - Aviation theories and other practices | Next
FIRE-FIGHTING EQUIPMENT |
Class B
Class B fires occur with flammable liquid
substances. Examples of class B fires are gasoline, jet
fuels, paints, grease, and any petroleum-based product.
These and other combustible substances do not leave
embers or ashes. Class B fires are extinguished by
providing a barrier between the burning substance and
oxygen necessary for combustion. Chemical and
mechanical foams produce such a barrier and are
known as permanent smothering agents, but their effect
is only temporary. The application must be renewed if
there is any danger of reignition. The extinguishing
agents recommended for combating class B fires are
CO2, PKP, Halon, and Aqueous Film-Forming Foam
(AFFF).
NOTE: Water by itself is NOT recommended for
use on class B fires.
Class C
Class C fires are energized electrical fires that are
attacked
at
prescribed
distances
by
using
nonconductive agents such as CO2 and Halon 1211.
The most effective tactic is to de-energize the system
and handle the fire as a class A fire. When fires are not
deep seated, clean agents that pose no cleanup problem,
such as Halon 1211 or CO2, are the preferred
extinguishing agents.
WARNING
Water in any form, particularly salt water, is
dangerous when used on electrical equipment.
Class D
Class D fires are combustible metals, such as
magnesium and titanium. Water in large quantities, as
high velocity fog, is the recommended extinguishing
agent.
When water is applied to burning class D
materials, there may be small explosions.
The fire
fighter should apply water from a safe distance or from
behind shelter.
Metal fires on board ships are
commonly associated with aircraft wheel structures.
EXTINGUISHING AGENTS
There are many materials that may be used as
fire-fighting agents. The primary agents discussed in
the following paragraphs are the most extensively used
aboard naval ships.
Water
Water is a cooling agent, and on board ship, the sea
provides an inexhaustible supply.
If the surface
temperature of a fire can be lowered below the fuel's
ignition temperature, the fire will be extinguished.
Water is most efficient when it absorbs enough heat to
raise its temperature to 212°F (100°C) or boiling point.
At this temperature, the seawater will absorb still more
heat until it changes to steam. The steam carries away
the heat, which cools the surface temperature.
Water in the form of fog is very effective for
fire-fighting purposes.
Additionally, water fog can
provide protection to fire fighters from heat. However,
the fog must be applied directly to the area to be cooled
if its benefits are to be realized.
Water in the form of a straight stream (also called
solid stream) is used to reach into smoke-filled spaces
or areas at a distance from the fire fighter. When a
straight stream is needed as an extinguishing agent, it
should be directed into the seat of the fire. For
maximum cooling, the water must come in direct
contact with the burning material. A straight stream is
best used to break up and penetrate materials.
Aqueous Film-Forming Foam (AFFF)
AFFF is composed of synthetically produced
materials
similar
to
liquid
detergents.
These
film-forming agents are capable of forming water
solution films on the surface of flammable liquids.
AFFF concentrate is nontoxic and biodegradable in
diluted form. When proportioned with water, AFFF
provides three fire-extinguishing advantages.
1.
An aqueous film is formed on the surface of the
fuel that prevents the escape of the fuel vapors.
2.
The layer effectively excludes oxygen from the
fuel surface.
3.
The water content of the foam provides a
cooling effect.
The primary use of AFFF is to extinguish burning
flammable or combustible liquid spill fires (class B).
AFFF has excellent penetrating characteristics and is
superior to water in extinguishing class A fires.
Carbon Dioxide (CO2)
CO2 is an inert gas and extinguishes fires by
smothering them. CO2 is about 1.5 times heavier than
air, which makes it a suitable extinguishing agent
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