Page 19 - Electrician - TT (Volume 1)

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Oxygen: Usually exists in sufficient quantity in air to keep a fire burning.
Extinguishing of fire: Isolating or removing any of these factors from the combination will extinguish the fire.
There are three basic ways of achieving this.

• Starving the fire of fuel removes this element.
• Smothering - ie. isolate the fire from the supply of oxygen by blanketing it with foam, sand etc.
• Cooling - use water to lower the temperature.
Removing any one of these factors will extinguish the fire.
Classification of fires: Fires are classified into four types in terms of the nature of fuel.

Different types of fires (Fig 2, Fig 3 Fig 4 & Fig 5) have to be dealt with in different ways and with different
extinguishing agents.

Fire Classification and Fuel Extinguishing Method

Fig 2
Most effective ie., cooling with water. Jets of water
should be sprayed on the base of the fire and then
gradually upwards.

Should be smothered : The aim is to cover the entire
Fig 3 surface of the burning liquid. This has the effect of cutting
off the supply of oxygen to the fire.
Water should never be used on burning liquids.
Foam, dry powder or CO2 may be used on this type of
fire.

Fig 4 Extreme caution is necessary in dealing with liquefied
gases. There is a risk of explosion and sudden outbreak
of fire in the entire vicinity. If an appliance fed from a
cylinder catches fire - shut off the supply of gas. The
safest course is to raise an alarm and leave the fire to be
dealt with by trained personnel.

Dry powder extinguishers are used on this type of fire.

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CITS : Power - Electrician & Wireman - Lesson 1- 4