How Fire Extinguishers Obtain Ratings

Fire extinguishers display a fire rating to indicate their fire extinguishing capability. To achieve a fire rating an extinguisher must consistently be able to extinguish a test fire of a specific class and size. The performance of an extinguisher in a real situation also depends on it`s maintenance and the skill of the user.

The fire rating is specific to the declared design and contents of the extinguisher. If these are altered the fire rating will need to be reassessed. If incorrect spare parts are used when servicing an extinguisher this could adversely affect the extinguisher and invalidate the fire rating.

The Classes Of Fire is identified by a letter A, B or F in the UK ratings do not exist for C or D, the size of fire is identified by a number, the larger the number the larger the test fire it can extinguish.

Example 1.  13A / 113B This rating indicates the extinguisher is capable of extinguishing a class A test fire of size 13A and a class B test fire of size 113B.

Example 2. 13A / 75F

This rating indicates the extinguisher is capable of extinguishing a class A test fire of size 13A and a class F test fire of size 75F.

Test fires for class A rated fire extinguishers

A metal frame support of 250mm high on top of which is placed wooden sticks in the form of a crib shape. The height of the crib is 560mm and the width is standard at 500mm.

The length of the crib is determined by the rating to be assessed. The fuel used for the test fire is industrial heptane.

Test fire are conducted indoors, water to a depth of 30mm is added to the tray along with the fuel, the fuel is ignited, allowed to burn for 2 minutes then the tray is withdrawn and the burning is allowed to continue for a further 6 minutes before the fire is finally allowed to be attacked.

The fire should be extinguished in 5 minutes, for fire up to and including 21A and 7 minutes for greater fires. There is to be no re-ignition within 3 minutes of extinction.

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