Foam fire extinguishers and how they are use

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Foam fire extinguishers are one of the most common types of fire extinguisher, and are generally used for fires involving flammable solids and liquids. Foam fire extinguishers create a cooling blanket effect, smothering burning materials and preventing re-ignition.

It is not for use on chip pan fires unless they are described specifically as class F extinguishers

 

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Also known as:

• AFFF foam fire extinguishers
• Spray foam fire extinguishers

How to identify a foam fire extinguisher:

• CREAM coloured label printed on the body stating ‘Foam’
• Should be identified by an extinguisher ID sign fixed nearby – ‘Foam Extinguisher’

Sizes of foam fire extinguisher available:

• 2 litre
• 3 litre
• 6 litre (most commonly used)
• 9 litre

Uses of foam fire extinguisher:

  • Fires involving flammable solids, such as paper, wood, and textiles (‘class A’ fires)
  • Fires involving some flammable liquids, such as petrol, diesel, and paint (‘class B’ fires)
  • Fires involving electrical appliances IF the extinguisher has passed the 35kv conductivity test

 

How foam fire extinguishers works:

Foam fire extinguishers work in 2 ways.

  1. They are mainly water-based and so have the same cooling effect as water extinguishers, putting the fire out by lowering the temperature.
  2. They contain ‘Aqueous Film Forming Foam’ (this is why they are also known as AFFF foam extinguishers).

AFFF works by smothering the fire and sealing in the flammable vapours. This prevents the fire re-igniting. It also allows foam fire extinguishers to put out flammable liquid fires, by creating a barrier between the liquid’s surface and the flames.

Advantages & Disadvantages of foam fire extinguishers:

Advantage:

  • Non-toxic, non-damaging to most materials, largely safe if accidentally used on electrical fires (although this is not recommended), designed to prevent the re-ignition fires, lighter in weight than the equivalent water extinguisher.

Disadvantage:

Damaging to electrical appliances. Dangerous if used on cooking fires or flammable gas fires.

 

How to use a foam fire extinguisher:

Aside from the basic steps of using the fire extinguisher which applies to all types of fire extinguisher, here are other things you should take note of depending on the type of fire:

Flammable liquids fires:

  • Do NOT spray directly at the fire, this can cause it to spread to nearby surfaces.
  • Where the liquid on fire is contained, point the extinguisher at the inside edge of the container.
  • If it’s not contained, spray with a gentle, sweeping movement across the TOP of the fire, or against an adjacent surface.
  • This way the foam will drop down and settle on the top of the burning liquid.

Flammable solids fires:

  • Aim at the base of the fire
  • Keep the extinguisher moving forwards and backwards across the flames as you spray

 

 

Please note: Foam extinguishers are not explicitly designed for use on electrical fires.

 

 

Further reading

Class K fire extinguishers and when to use them

6 Major types of fire extinguishers and their purposes

Fire extinguisher regulations: OSHA & General Regulation

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