Understanding Foam Fire Extinguishers
Foam fire extinguishers
can be used to fight:
- Class A: Ordinary combustibles: wood, paper, cloth, rubber and plastics
- Class B: Flammable liquids (petrol, oil, spirits and grease)
How to identify them
Foam fire extinguishers have red writing on a yellow label. However, you’ll need to mount a foam fire extinguisher sign
next to it.
How foam extinguishers work
Foam extinguishers work by blanketing the fire in a layer of foam that seals out oxygen and cools the source of fuel. This cooling barrier also prevents the fire from re-igniting.
When to use foam fire extinguishers
Foam fire extinguishers are used to fight class B and class C fires.
They’re particularly useful when fighting petrol and volatile liquid fires so they’re a great choice for garages and petrol stations.
Other benefits of a foam fire extinguisher
The foam in the extinguisher is non-toxic, and it won’t impair visibility. They’re also generally smaller than their water counterparts that achieve the same fire rating. This makes them easier to handle.
AFFF foam fire extinguishers
AFFF is the most common type of extinguisher foam. AFFF is an acronym for Aqueous Film Forming Foam.
AFFF foam is a synthetic fire extinguisher foam that’s known for its strong flame knock down and cooling properties, which prevent re-ignition.
AFFF foam is also self-healing, which means the foam layer will repair itself if damaged or cracked.
Protein foam fire extinguisher
There are several types of protein foam, but the one you probably recognise is FFFP, which stands for Film Forming Fluoroprotein Foam.
Protein foams use naturally occurring proteins, which causes the foam agent to be stiffer. This stiff foam is heat resistant and extremely durable. It also has a strong burn back resistance.
Some synthetic foams, will lower the flash point of some fuels, making them more flammable. This is not a risk for protein based foam; because protein foam is stiffer, it also has a slower release. This means that it is takes more time to extinguish a fire, and some protein foams are unsuitable for refilling standard fire extinguishers. If in doubt, check with the supplier before you buy.
Alcohol-resistant (AR-AFFF) foam extinguishers
With standard foam, alcohol will mix with the water base, causing the foam layer to collapse. A high molecular polymer is added to alcohol resistant foam during the manufacturing process.
This polymer forms a protective membrane between the foam layer and the fuel.
What does the drainage rate mean?
The drainage rate indicates how long it will take for 25% of the foam solution to drain from the foam layer. This is also known as the quarter life or 25% drain time.
Foam that has a fast drainage time is normally very fluid and spreads quickly across the fuel surface of a fire. Foams with longer drain times move more slowly across the fuel surface.
What is a foam’s expansion rate?
The expansion rate is a ratio showing how much final foam is created from the initial foam solution when you use the extinguisher. For instance, if one cubic metre of foam creates 10 cubic metres of foam when activated, the expansion rate would be 10:1
There are three expansion rate classifications:
- Low expansion – less than, or equal to 20:1
- Medium expansion – between 20:1 and 200:1
- High expansion – greater than 200:1
Refilling your extinguisher – what a foam’s concentrate tell us?
Extinguisher foam is made of three components – water, air and foam concentrate.
When your extinguisher is filled/refilled, the foam refill drum used will have a foam concentrate percentage on them. This indicates what proportions of foam and water should be mixed to create the final solution.
Let’s take the example of a 3% foam concentrate. If you were making a 100ml solution, 3ml would be foam concentrate and 97ml would be water would be mixed to create a 3% solution.
Of course, the lower the foam concentrate is, the less of it you’ll need to use per refill, which is better more economical.
Any foam that is water based should not be used on electrical equipment as the water component is a conductor of electricity. If you use a foam fire extinguisher on electrical devices, you could receive an electric shock.
When using with powder extinguishers
If you use a dry powder extinguisher
with a foam extinguisher, make sure the powder is foam compatible.