Fire Engineering - Chapter 05. Fire Extinguishing Method

1. Fire Extinguishing Method

i) Cooling

Heat may be removed and brought below the ignition point of the substance involved by pouring water that is called cooling.

ii) Starvation

The fire may be extinguished by removing the combustible material from the scene of the fire that is called starvation.

iii) Smothering (Blanketing)

The fire may be extinguished by removing oxygen or stopped oxygen supply that is call smothering.

2. Branching of Chemical Chain Reaction

The chemical reactions in a flame take place very quickly at a very high temperature, and in a very small volume. All flame reactions depend largely on the activities of stray bits of molecules of the reacting substances. These little fragment are very reactive, very unstable, and can exist for a fraction of a second; also, these molecules are extremely mobile.

For example:-

2H₂ + O₂ = 2H₂O  

In this reaction, hydrogen atoms(H), oxygen atoms(O) and hydroxyl radicals (OH) react in the form of completely free ions. In a flame they have sufficient concentration & the series of reactions that may possibly take place may be represented by ‘O’ + H2       OH + H. the arrow indicates that it is a part of the complete process and not a balanced reaction, and the asterisks are used to indicate the molecular fragments or free radicals.