This extinguisher must never be used on liquid fires or fires involving or next to live electrical equipment. Foam Firefighting foams have been developed primarily to deal with the hazards posed by liquid fuel fires. Finished firefighting foams consist of bubbles that are produced from a combination of a solution of firefighting foam concentrate and water that has then been mixed with air. These air-filled bubbles form a blanket that floats on the surface of flammable liquids. In so doing, the foam blankets help to knock down and extinguish these fires in the following ways: • By excluding air (oxygen) from the fuel surface, smothering • By separating the flames from the fuel surface • By restricting the release of flammable vapour from the surface of the fuel • By forming a radiant heat barrier, which can help to reduce heat feedback from flames to the fuel and, hence, reduce the production of flammable vapour By cooling the fuel surface and any metal surfaces as the foam solution drains out of the foam blanket. This process also produces steam, which dilutes the oxygen around the fire. Dry Chemical Powders This type can be used on most classes of fire, including electrical equipment. Dry Powder is very effective at extinguishing flames ("rapid knock-down") by smothering. Dry Chemical is expelled from containers by gas pressure and directed at the fire in a concentrated cloud by means of specially designed nozzles. This cloud also screens the operator from the flames and enables a relatively close attack to be made but has the downside of obscuring the operator's view as well as causing problems to the operator from inhaling the powder, especially if used indoors. It is worth bearing in mind that with this type of extinguisher, there is a risk of the fire re-igniting. Powder can be used on live electrical fires but there is a chance that the equipment may be damaged. Carbon Dioxide Best for Live electrical equipment, although it allows the re-ignition of hot plastics. Now mainly used on large computer servers, although care must be taken not to asphyxiate people when using the extinguisher in small server rooms. Carbon dioxide extinguisher works by suffocating the fire. Carbon dioxide displaces oxygen in the air. Wet chemical Best for Class F fires, involving cooking oils and fats, such as lard, olive oil, sunflower oil, maize oil, and butter. The potassium acetate the extinguisher discharges are transformed into a fine mist. This can corrode certain metals and cause irritation to the skin and eyes.
©SHEilds – All rights reserved FC V 5 JUN 2021
Page 33 of 41
Made with FlippingBook Digital Publishing Software