Extinguishing a fire

• The essential conditions for a combustion are: Fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature).
• Fire can be controlled by removing one or more of these requirements.

Use of Water:

• Water can be used to extinguish a fire. Water evaporates taking away heat from the fire, which in turn cools down the burning material below its ignition temperature. Use of water in some cases can be dangerous.

1. Water should never be thrown on a liquid fire

• Water does not mix with the oil, water being heavier than oil goes beneath them and substance continues burning.
• Water boils and become steam very quickly. Since water is at the bottom of the oil, as it evaporates it sprays hot, burning oil in every direction. This then spreads the fire.
• Liquid fires can be stopped by using Fire extinguisher.

2. Water should not be used over electrical fires, as it conducts electricity and can pose danger to people trying to extinguish the fire.

The steps to extinguish electrical fires:

• Turn off all power to the fire, usually done by turning off the main power
• This step alone is usually enough to stop most fires in the initial stages.
• The safest and the best way to extinguish an electrical fire is to use a fire extinguisher.

Fire extinguishers:

• Fire extinguishers make use of carbon dioxide gas as it is not a supporter of combustion. Being heavier than air, carbon dioxide settles down and cuts off the supply of oxygen, which extinguishes the fire.
• Two common types of fire extinguishers are carbon dioxide fire extinguisher and soda-acid fire extinguisher.

Carbon dioxide fire extinguisher:

• This type of fire extinguisher consists of carbon dioxide filled under high pressure in cylinders.
• Carbon Dioxide fire extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure. The pressure in the cylinder is so high that when you use one of these extinguishers, bits of dry ice may shoot out the horn. CO₂ fire extinguishers are useful for flammable liquid and electrical fires only.
• Carbon dioxide extinguishes fire by forming a blanket over fire thus cutting off the supply of oxygen. The carbon dioxide is also very cold as it comes out of the extinguisher, so it cools the fuel as well.
• CO₂ fire extinguisher may be ineffective in extinguishing Class A fires (caused by paper, wood, card board and most plastics) because they may not be able to displace enough oxygen to successfully put the fire out. Class A materials may also smolder and re-ignite.

Soda-acid fire extinguisher:

• This type of fire extinguisher contains concentrated solution of sodium hydrogen carbonate and sulphuric acid in separate compartments.

• When the fire extinguisher is used, the two substances come into contact with each other, producing carbon dioxide.