Page 370 - IGC BOOK

of a blanket of foam or a fire blanket.

Removing the Heat
Extinction by this process is known as cooling. Cooling with water is the most common means
of fighting a fire and this has a dual effect in terms of absorbing heat and thereby reducing
the heat input into the fire, and reducing the oxygen input through the blanketing effect of
the steam produced.

Although water is the most common medium used to fight fires, it is by no means the only or
the most suitable substance. Indeed, using water on certain types of fire can make the
situation worse.

The main different types of extinguishing media are described below, and you should note
their application to the classification of different types of fire.

Water

Water applied as a pressurized jet or a spray is the most effective means of extinguishing class
A fires, and may also be used as a spray on class B fires involving liquids and liquefied solids
which are miscible (capable of mixing) with water, such as methanol, acetone and acetic acid.
Whilst ineffective on class C fires themselves (those involving gases), water may be used to
cool leaking containers.

It must never be used on fires involving electricity, as the current can flow up the stream of
water, nor on non-miscible liquid fires as only a cupful of water can cause the whole fire to
erupt into a conflagration.

Foam

Foam is a special mixture which forms a smothering blanket over the fire, cutting off the
supply of oxygen. It can be used on class A and B fires (although there are some restrictions
in its use on class B fires since certain types of foam break down in contact with alcohols) and
also on small liquefied gas fires (which make up certain class C fires).

Using foam as an extinguishing agent demands considerable skill when dealing with anything
but very small-scale liquid fires, since the procedure is to start at the rear and to lay a blanket
of foam across the surface of the liquid.

ENSIGN | Unit IG2 – Element 10 –Fire 25