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Know Your Fire Extinguishers

There are many types of Fire Extinguisher and it is extremely important to have the right one available for the type of fire hazard you might encounter. For example, extinguishing a fire caused by a faulty electrical device using a water fire extinguisher could lead to electrocution. In this situation the ideal extinguisher would contain carbon dioxide or powder, neither of which conduct electricity. Fires themselves are classified into different types, depending on the material that is burning. The extinguishers are also classified according to which classes of fire they can be used against.
All fire extinguishers work by removing one or more of the 3 key ingredients of a fire – heat, oxygen and fuel. The diagram below illustrates this and is called the FIRE TRIANGLE.FireTriangle

DON’T FORGET:
• Don’t attempt to use an extinguisher on a fire unless you feel it is safe for you to do so.
• If you are using a fire extinguisher on a fire, keep yourself on the escape route side of the fire.

Here is a summary of the different types of fire extinguisher and their recommended uses.

which fire extinguisher to use chart

In the UK, Fire Extinguishers must be manufactured to BS5423 or BS EN1869 ensuring they are fit for purpose.

Water Fire Extinguishers
Water Fire Extinguishers are used for burning wood, paper and soft furnishings (these are called Class A fires). The water soaks the material, removing the heat and extinguishing the fire.
Advantages:
• Doesn’t contain harmful chemicals

Disadvantages:
• Low fire fighting rating (smaller discharge time) due to large size and weight
• Can’t be used on electricity (as water is a conductor)
• Can only be used on Class A fires
Hydrex Extinguishers
These extinguishers are very similar to water extinguishers, but contain an additive which reduces their electrical conductivity. They are not designed for use on electrical fires, but can be used safely near electrical appliances and power sockets without fear of electrocution. Hydrex extinguishers are typically used in homes and places where children have access to them, or where they may be accidentally set off.
Advantages:
• Suitable for many environments where there is a risk of Class A or Class B fires
• Can be used safely near sources of electricity
• Higher fire fighting rating (longer discharge time) than plain water extinguishers

Disadvantages:
• The liquid in the extinguisher will damage electrical equipment such as computers (although these may of course have already been damaged by the fire itself)
AFFF Foam Fire Extinguishers
Foam fire extinguishers contain water and a foaming additive and work by forming a layer of film across the burning materials, starving them off oxygen. The water in the extinguishers also works on the fire by absorbing much of the heat. These extinguishers are suitable for Class A and Class B fires, including petrol and other flammable liquids and can also be used on furnishings where man-made fibres can turn to liquid in the intense heat of a fire.
Advantages:
• Suitable for many environments where there is a risk of Class A or Class B fires
• Can be used safely near sources of electricity
Disadvantages:
• The liquid in the extinguisher will damage electrical equipment such as computers (although these may of course have already been damaged by the fire itself)

ABC Dry Powder Fire Extinguishers
Dry Powder Fire Extinguishers can be used on Class A, B,C and Electrical fires and are very quick and effective at putting fires out. You have to be careful the fire is completely put out when using a Powder extinguisher as it only removes the oxygen element from the fire, so the residual heat may re-ignite the fire. The main problem with these extinguishers is the powder, which can cause breathing difficulties, causes a ‘fog’ which can hinder evacuation and is also extremely messy to clear away. British Standards no longer permit ABC Powder Extinguishers to be used in offices and living accommodation due to this problem. ABC Powder extinguishers are therefore only recommended for use in well-ventilated areas.
There is also a BC Powder Extinguisher, specifically manufactured for use in vehicles.
Advantages:
• Can be used on Class A, B,C and Electrical fires
• High fire fighting rating
Disadvantages:
• Powder can cause breathing problems, so they may only be used in well-ventilated areas
• Can hinder evacuation due to the powder ‘fog’ created
• Powder damages soft furnishings, carpets, computer drives etc
Dry Special Powder
This is a specialist extinguisher is for use on burning metals (class D fires) only, and works by removing the oxygen from the fire triangle. The extinguishers are equipped with a special low velocity applicator to ensure the fire fighting powder is applied efficiently and effectively to the burning material and to prevent the swarf from spreading. Again, the powder can cause breathing problems and is messy to clear up, but they provide the only approved option for a Class D fire risk.
Advantages
• The only approved option for a Class D fire
Disadvantages
• Powder causes breathing problems
• Can hinder evacuation due to the powder ‘fog’ created
• Messy to clear up

Carbon Dioxide (CO2) Fire Extinguishers
These extinguishers contain CO2 at high pressure and are suitable for Class B and Electrical fires. They won’t damage computers or other electrical equipment and are often sited alongside a water or foam extinguisher to cover the widest range of fire types. If you ever need to put out an electrical fire, remember to turn off the power supply to the equipment to ensure the equipment doesn’t re-ignite. You must also remember to avoid holding the horn as you deploy the extinguisher since it gets cold enough to freeze to your skin as the pressurised CO2 gas is forced out. CO2 extinguishers are not suitable for deep fat fryers since the force of the escaping gas can carry burning fat across the room.
Advantages
• Suitable for electrical fires
• Lightweight

Disadvantages
• Fires can re-ignite once the gas runs out if the power supply remains on
• Horn gets very cold during use and can cause freeze-burn if touched

Wet Chemical Fire Extinguishers
These are specifically designed for use on kitchen fires involving burning oil and deep fat fryers (Class F fires). They work be enabling a layer of chemical foam to be created on top of the fire from a safe distance. They may also be used on Class A fires.
Advantages
• Effective for use on kitchen fires involving burning oil and fat
Disadvantages
• Water and chemicals may damage equipment

DON’T FORGET:
• Don’t attempt to use an extinguisher on a fire unless you feel it is safe for you to do so.
• If you are using a fire extinguisher on a fire, keep yourself on the escape route side of the fire.

Summary of Classes of Fire
Class A Fires: involving freely burning materials e.g. wood, paper. textiles
Class B Fires: caused by combustion of liquids or material that will liquefy
Class C Fires: involving flammable gases e.g. butane, propane
Class D Fires: involving flammable metals e.g.magnesium, lithium
Electrical Fires: Fires involving electrical equipment e.g. photocopiers, computers
Class F Fires: involving cooking oil and fat e.g. olive oil, maize oil, lard

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