FIRE & FIRE EXTINGUISHERS & CLASSES

 INTRODUCTION

“Fire is a rapid, self sustaining oxidation process accompanied by the evolution of heat and light of varying intensity”. Fire results from the combination of fuel, heat and oxygen when a substance is heated to a certain critical temperature called the “Ignition Temperature”. The material will ignite & continue to burn as long as there is fuel, the proper temperature and a supply of oxygen (air). Classification of Fires is mentioned below:

 CLASSES OF FIRE EXTINGUISHER

Class “A” Fires: 

These are fires involving solid materials (such as wood, cloth, paper, rubber, etc.), normally of an organic nature (compounds of carbon), in  which combustion generally occurs with the formation of glowing ambers, where the cooling effect of water is essential for extinguishment of fire.

 

Class “B” Fires: 

These are fires involving flammable liquids e.g. kerosene, naphtha, LDO, mix oil, gasoline, where blanketing effect (A layer of foam over the surface of burning liquid) is essential for extinguishing fire.

 

Class “C” Fires: 

These are fires involving gases e.g. LPG, Methane, Ethylene, Propylene, Hydrogen etc. Fire can be put out either by dry chemical powder or carbon dioxide gas. Here isolation of leaking source is essential.

Class “D” Fires: 

These are fires involving combustible metals, such as magnesium, titanium, sodium. These fires can be put out with the help of special dry powders. Ordinary DCP or Foam or Water is of no use on such fires.

 

Electrical Fires:

 According to latest concept, electrical fires do not constitute a particular class. Any fire involving electrical equipment is a fire of class A or class B. The normal procedure in such fires is to cut off the electrical supply of the equipment and to use an extinguishing media appropriate to the burning material. Water in the form of hose stream should in no case be used in electrical fires unless positive isolation of electric supply has been ensured.

CLASSIFICATION OF FIRE AND SUITABILITY OF PORTABLE FIRE EXTINGUISHERS

S/No.	Class of Fire	Foam Extinguisher	Carbon Dioxide Extinguisher	Dry Chemical Powder Extinguisher
1	Class A Fire	Suitable	Not recommended except for small surface fire	Suitable
2	Class B Fire	Suitable	Suitable	Suitable
3	Class C Fire	Not Suitable	Suitable	Suitable
4	Class D Fire	Not Suitable	Not Suitable	Special dry powder
5	Electrical Fire	Not Suitable	Suitable	Suitable

Caution:-

1)    Do not use Foam Fire Extinguisher on fires involving live electrical equipment and metal.

2)    Do not use CO2 Fire Extinguisher on big size fire. It is also not to be used on metal fire. While extinguishing oil fire, precaution against flash back  or re-ignition  is to be taken.

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