Fire extinguishers are an absolute necessity in any workplace. We’ll see in this article exactly what fire extinguishers do and how they do it. Typically a reaction between oxygen in the atmosphere and some sort of fuel, fire is the result of a chemical combustion reaction. For the combustion reaction to take place, the fuel has to be heated to its ignition temperature. Here’s the sequence of events in a typical wood fire:

• Something heats the wood to very high temperatures.
  
• The heat decomposes some of the cellulose material that makes up the wood when it reaches about 150 degrees Celsius.
  
• Volatile gases are released from the decomposed material, usually a compound of hydrogen, carbon and oxygen.
  
• The compound molecules break apart when the gas is hot enough, and the atoms recombine with the oxygen to form water, carbon dioxide and other products.
  
• The flame is made up of the gases, which rise through the air.
  
• The heat of the flame keeps the fuel at ignition temperature, so it continues to burn as long as there is fuel and oxygen.

Fire extinguishers play a key role at the beginning of a fire. Fire extinguishers and hoses can be used to put out a small blaze, but their chief function is to help people make their way out of a burning building. Extinguishers should be placed a maximum of 30m apart, and you need one extinguisher for every 200m² of floor area, according to current recommended practice.

The first line of defence would be from extinguishers that contain water or foam. For smaller buildings it is acceptable to use multipurpose extinguishers, such as the 2kg dry powder type. Make sure to check extinguishers monthly to ensure that they are properly stored, charged and undamaged. Check the gauge to make sure the extinguisher is still charged, and the seals to make sure they have not been tampered with. You should have rechargeable extinguishers recharged, and disposable ones replaced once you use them.

Fire extinguishers are a very important safety item, and they should be mounted in an easily accessible place. You can use the red water extinguisher on Class A fires, i.e. fires that involve wood, paper and textiles. Do not use water type extinguishers on live electrical equipment, due to the risk of electric shock. You should also avoid using it on flammable liquids, since water causes this type of fire to spread. You can use it in all areas of the building for general fire protection, with a minimum of two per floor.

Foam extinguishers, which are cream in colour, are good for Class A (wood, paper, textiles) and Class B (flammable liquids) fires. Foam should not be used on live electrical equipment. You can place them in all areas of the building, especially where flammable liquids may be present. Since not all fires can be put out with a fire extinguisher, a fire blanket should be fitted in kitchens.

Since blue powder type fire extinguishers can be used on Class C (gas) and Class E (electrical) fires, they can be placed in all locations, in addition to water and foam extinguishers. Note that not all powder extinguishers may be used on Class A fires. However, they provide good backup for other kinds of fire extinguishers.

The substance in fire extinguishers work to put out small fires by cooling the burning material, depriving the flame of oxygen, or interfering with the chemical reactions occurring in the flame. Water performs two of these functions: its conversion to steam absorbs heat, and the steam displaces the air from the vicinity of the flame.