Fire Extinguisher Class

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What Does A Fire Extinguisher Class Tell Us?

A fire extinguisher class is given as a combination of letters and numbers and is intended to give you information on the class of fire that the appliance should be used on and the size of fire that it is capable of dealing with. The code on an appliance may include more than one letter if it is safe to use on more than one type of fire. I will explain about the different fire classifications and how these relate to extinguisher codes below.

Fire Extinguisher Codes – The Letter

As mentioned earlier, the letter part of a fire extinguisher class refers to the type of fire that it can be used to put out. All fires are classified in a standard way in the UK and given a corresponding letter. It is the letters representing each fire class that is used on the fire extinguisher. The standard fire class elements are as follows:

Fire Extinguisher Class A

These fires are those involving organic matter such as wood, paper, fabrics, etc.

Fire Extinguisher Class B

These involve flammable liquids such as petrol or diesel, or liquefiable solids.

Fire Extinguisher Class C

These involve flammable gases such as butane or propane. In the US there is no separate class for gases, which are included under class B.

Fire Extinguisher Class D

These involve combustible metals or alloys such as magnesium, sodium or potassium.

Fire Extinguisher Class F

These fires involve burning oil or fat. In the US these are known as Class K.

Extinguishers For Electrical Fires

There is no separate classification for electrical fires in the UK, though these are categorised separately in the US as Class C.

Fire Extinguisher Codes - What The Numbers Mean

The numerical element of the codes represents an indication of how much fire that appliance is capable of extinguishing. This is not just a general estimate, it is based on being specifically measured against a standardised test. I will not go through all the details of all the tests used, but to give you some idea of how precise they are, here are some examples:

Tests For Class A Fires

The numerical part of the extinguisher codes for class A fires is established by the use of a wooden crib test. This is essentially a crib shaped arrangement of wooden sticks that present a precise amount of combustible material for each test type. The crib is made up or rows of sticks stacked in layers to a set standard height. The width and length of the crib is determined by the test being carried out and effectively controls the exact quantity of burning wood to be extinguished.

For example, to test for a 13A fire extinguisher class, the crib would consist of 13 sticks in its width and each stick would be 1.3 metres long. A test for 27A would have layers 27 sticks wide and the crib would be 2.7 metres long. All test fires are lit in exactly the same way and allowed to burn for a set time before the extinguisher can be used. The appliance must extinguish the fire within a fixed period of time to pass the test and achieve that classification.

Tests For Class B Fires

Class B fires are fires on liquid, so these tests are all carried out in special standard steel trays. The tray is of a fixed height and a precise amount of liquid fuel and water is put into the tray and ignited. A fire extinguisher class of 21B would require that the appliance puts our a fire in a tray containing 21 litres of liquid in a fixed time, whereas a class of 70B would require it to extinguish a fire on 70 litres of liquid, etc.

Fire Extinguisher Colour Codes

The following is a list of the standard colours for different types of fire extinguisher:

Water – Red

Carbon Dioxide – Black

Dry Powder – Blue

Foam (AFFF) – cream

Wet Chemical - Yellow

Vapourising Liquids - Green

Fire Extinguisher Class

Understanding The Code and Class Of A Fire Extinguisher