By David Bonnet
Marketing Manager, Chubb Fire Limited
Originally published in International Fire Fighter Magazine
A portable fire extinguisher is a vital piece of potentially life-saving equipment which we should choose with great care and properly maintain. There a are a range of portable extinguishers available for different types of fire.
Fires divide into the following classes:
- Class A freely burning fires fuelled by ordinary combustible materials e.g. cloth, wood and paper.
- Class B fires fuelled by flammable liquids such as oils, spirits, petrol and greases.
- Class C fires fuelled by flammable gasses such as Propane and Butane
- Electrical fires
Portable fire extinguishers divide into the following categories:
1. Water for use on Class A fires; is usually expelled under pressure forming a controllable long jet which cools the burning material by absorbing heat. It is highly dangerous if used on live electrical equipment.
2. Newer water with additives extinguishers offer a much greater firefighting capacity than traditional water extinguishers. The content is expelled in a spray around four meters in length, which cools the burning material and inhibits the propagation of the fire. Although not generally suitable for live electrical equipment, some manufacturers' products have passed a 35 kv electrical conductivity test, which means if accidentally used on live electrical equipment, the risk of electrical shock is substantially reduced.
3. Spray foam AFFF for Classes A and B fires; is expelled in a spray which forms a blanket on top of the burning material/liquid, cooling and excluding oxygen, sealing the surface and preventing re-ignition. Again although not generally suitable for live electrical equipment, some manufacturers' products have passed the 35 kv electrical conductivity test.
4. Carbon Dioxide is suitable for use on live electrical equipment as it is an non-conductive agent. However as a safety precaution, the power supply should be disconnected wherever it is possible. CO2 can also extinguish Class B fires by excluding oxygen. It is non-toxic, clean to use and harmless to most delicate equipment such as computers, however it can be dangerous if used in a confined space as it can asphyxiate. It is expelled under great pressure in a powerful concentration, reducing oxygen in the air, but because it has little cooling effect, re-ignition can occur. These extinguishers can also cause freeze burns if the nozzle or base comes into contact with skin.
5. Dry powder is a highly versatile fire fighting medium for Class A, B and C fires as well as live electrical hazards. It is also effective for vehicle fires and suitable for most risks. Powder knocks down the flames by chemically inhibiting combustion, but re-ignition can occur and it does not readily penetrate the inside of electrical equipment. Also, when used inside buildings it is likely to reduce visibility. In addition there is a type of dry powder (BC) developed for use in areas of special risk, such as in the petrochemical industry, which will not deal with Class A fires, but which can be used at the same time as foam liquids.
6. Wet chemical for Class F (deep fat) fires provides a two-pronged fire fighting effect, by knocking out the flames in seconds, then capping the oil with a 'soapy' crust, which prevents re-ignition. Some manufacturers' products are also effective on Class A fires.
Portable fire extinguishers are an important and tested means of preventing small fires from becoming large conflagrations.
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