Page 371 - IGC BOOK

Dry Chemical Powder

The powder is sprayed as a cloud over the fire, again acting to smother the supply of oxygen.
It can be used on class B fires and on small, liquefied gas fires (within class C). Specialized dry
powders using inert substances are also used on class D fires, where they form a crust over
the burning metal and thus exclude the oxygen.

Dry powders are also effective on fires involving electricity.

Carbon Dioxide Gas

This works by means of smothering the supply of oxygen. It is effective on class B fires and
also for electrical fires as the gas can enter into the inside of the equipment.

Wet Chemical

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Specifically designed to deal with high-temperature (>360 C) oil / fat fires (Class F). It reacts
with burning oil to form thick suds, cooling and emulsifying the oil, putting out the flames and
sealing the surface.

Vaporizing Liquids
When applied to a fire these agents produce a heavy vapor which extinguishes the fire by
excluding oxygen. They are safe to use on class A and B fires and are particularly effective on
fires involving live electrical equipment, since they interfere with electrical combustion
reactions.

1.Water (APW)

APW’s extinguish fire by taking away the “Heat”
element of the Fire Triangle.

APW’s are designed for Class A fires only: Wood,
paper, cloth. Here are a couple of reasons you need
to be careful about which extinguisher you use:

• Using water on a flammable liquid fire could cause
the fire to spread.

• Using water on an electrical fire increases the risk
of electrocution. If you have no choice but to use Water (APW)
an APW on an electrical fire, make sure the electrical
equipment is unplugged or de-energized.

ENSIGN | Unit IG2 – Element 10 –Fire 26