Introduction to Health and Safety at Work

Introduction to Health and Safety at Work
206
13.4 
Methods of extinction
There are four main methods of extinguishing fi res, 
which are explained as follows:
➤
cooling
– reducing the ignition temperature by tak-
ing the heat out of the fi re – using water to limit or 
reduce the temperature
➤
smothering
– limiting the oxygen available by 
smothering and preventing the mixture of oxygen 
and fl ammable vapour – by the use of foam or a fi re 
blanket
➤
starving
– limiting the fuel supply – by removing the 
source of fuel by switching off electrical power, isolat-
ing the fl ow of fl ammable liquids or removing wood 
and textiles, etc.
➤
chemical reaction
– by interrupting the chain of 
combustion and combining the hydrogen atoms with 
chlorine atoms in the hydrocarbon chain for example 
with Halon extinguishers. (Halons have generally been 
withdrawn because of their detrimental effect on the 
environment, as ozone depleting agents).
13.5 
Classifi cation of fi re
Fires are classifi ed in accordance with British Standard 
EN 2:1992 Classifi cation of Fires.
However for all prac-
tical purposes there are FIVE main classes of fi re – A, B, 
C, D and F, plus fi res involving electrical equipment. BS 
7937:2000 
The Specifi cation of Portable Fire Extinguishers 
for Use on Cooking Oil Fires
introduced the new class F. 
The categories based on fuel and the means of extin-
guishing are as follows:
Class A 
– fi res which involve solid materials such as 
wood, paper, cardboard, textiles, furniture and plastics 
where there are normally glowing embers during com-
bustion. Such fi res are extinguished by cooling which is 
achieved using water