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Fire Extinguishers



Portable fire extinguishers are essentially used:

  • for first attack firefighting of fires in their incipient stage
  • to assist in the suppression and/or mopping up of certain types of developed fires.
  • in some cases, to suppress unusual types of fires.

They come in a variety of sizes and are colour-coded to identify their contents.

 

Water Extinguishers

These are painted all red. The water is ejected through the nozzle by a CO2 gas cartridge or by stored pressure typically nitrogen gas. These are used on Class A fires (wood, paper, fabric). They are typically 9 to 10 litres capacity and can project a jet of water about 6 metres. For the best effect the water stream should be directed at the burning material.

 
   
  


 Foam Extinguishers

These are painted red with a blue band or label. The contents are ejected about 4 to 5 metres by a gas cartridge or by stored pressure and they are about 9 litres in capacity. These are used on Class B fires (liquids such as petrol, paints, oils etc). For the best effect the foam should be applied to fall as lightly as possible onto the burning material. This can be achieved by applying the foam to a rear wall in the case of a enclosed area, or if in an open space aiming the foam to strike the ground just short of the fire so that it flows gently over the burning fuel.

They may be used on Class A fires. Class F fires area best fought with a wet chemical extinguisher, but foam may also be used with good effect. A common type of foam extinguisher the AFFF. 

   

 

 

 AFFF

(Aqueous Film Forming Foam.) is a synthetic, non-toxic, amber coloured foam-forming liquid concentrate. It is scientifically designed product based on fluoro-chemical wetting agents and its unique action is connected with its ability to make water float on flammable fuels which normally float on water. The foam is formed by mixing the water/concentrate solution with air. It is deposited on the surface of the fuel as a thick rapidly spreading flame quenching blanket, resisting mechanical disruption and heat. hen the foam hits the fuel surface the water-floating action begins. The water dropping out of the foam bubbles floats on top of the fuel as a thin film preventing reflash or burning back of the extinguished surface. The water from the foam is not lost and goes where its cooling surface filming effects can do the most good. AFFF has proved to the most effective foaming type agent and shows speed and efficiencies of 300-400% better than protein type air/foam concentrates.

 

Dry Chemical Powder (DCP)

These are painted red, with a white band or labels and the contents are ejected by a gas cartridge or by stored pressure. They are used on Class B fires, that is on flammable liquid fires to assist foam in the combined-agent suppression. They are safe to use on live electrical equipment, but are generally not preferred for this role because of the clean-up afterwards. They range in size from 1kg to 11kg, though 9 kg is the most common. The ‘standard’ powder is sodium bicarbonate, but a number of high performance powders are also in use. Dry chemical powder is most effectively applied to flammable liquid fires in a low sweeping motion so as to apply a cloud of powder over the fire area. There is a possibility of re-ignition once the powder has dispersed from concealed flames or hot spots. When applied to ‘running fuel fires’ the powder should be directed first at the lowest parts of the fire and gradually worked upwards.

DCP extinguishes are rated as either ‘ABE’ or ‘BE’. This will be indicated on the label. As well as Class B fires, both types are considered suitable for Class C and E fires. The ABE type is suitable for class A fires but not Class F, and the BE type has limited effectiveness on Class F but is not effective on Class A fires.

Whilst Carbon dioxide (CO2) is non-toxic it can suffocate when in excessive quantities (such as in an enclosed cabin space). However this is unlikely when using a hand held extinguisher. 

   

 


Carbon Dioxide (CO2)

These are painted red with a black band or label. They are used as a first attack on electrical fires. The portable units vary in size from 2.5 kg to 7 kg. CO2 is a colourless, odourless gas, which does not support combustion. It is not poisonous but is suffocating in large quantities. The gas is discharged through a wide ‘horn’ discharge nozzle and the gas stream projects for 1 to 2 metres. This discharge is accompanied by a large roar and the gas is intensely cold, and can cause frostbite. It is applied in a low sweeping motion at the base of the fire, and the possibility exists for re-ignition after the gas disperses. However it leaves no mess or residue and is therefore preferred for electrical fires. Care should be taken though that it does not freeze electronic equipment.

If used outdoors, any breeze will disperse the gas and render the extinguisher

 ineffective. CO2 extinguishers also have limited effectiveness on Class A, B C and F fires.


 
 

    



Vaporising Liquids

These are painted red with a yellow band or label. They are effective for Class E fires and also suitable for Class A fires. They have limited effect on Class B or C fires and are not considered suitable for Class F fires.




 Wet Chemical

These are painted red with an oatmeal band or label. They are sometimes known as “NAFEX” extinguishers and are used especially for Class F fires – cooking fats and oils. They extinguish by saporification – converting the fat/oil into a soap-like mixture by treating it with an alkali. Because of the alkali solution, it has highly corrosive properties.














 


























Subpages (1): Fire Extinguisher Chart
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