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December 2005: Fire Extinguishers

Portable fire extinguishers can be a first line of defense in the early stages of a fire. With proper training, they can be very effective is preventing a small fire from growing rapidly out of control.

There are several types of fire extinguishers available. The selection process should be based on the character or Class of the fire anticipated. An occupancy such as an office would require a different extinguisher than would a flammable liquid operation.

The Classes of fires are as follows:

Classification of Fires
Class A
Fires in ordinary combustible materials, such as wood, cloth, paper, rubber and many plastics.
Class B
Fires in flammable liquids, combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols and flammable gases.
Class C
Fires that involve energized electrical equipment.
Class D
Fires in combustible metals, such as magnesium, titanium, zirconium, sodium, lithium and potassium.
Class K
Fires in cooking appliances that involve combustible cooking media (vegetable or animal oils and fats).

There are also multi-use extinguishers, such as an A-B-C that can be used on a Class A, Class B or a Class C fire.

Typically, at a minimum, portable fire extinguishers are sized at 2½ lbs. There should be one extinguisher for every 3,000 sq. ft. of floor area. They should be spaced such that the maximum travel distance is not greater than 75 ft.

The above size and area covered requirements can be different depending upon the hazard involved. NFPA Standard 10, "Standard for Portable Fire Extinguishers" and FM Global Data Sheet 4-5, "Portable Fire Extinguishers" reference various occupies/operations that would require difference sizes and spacing.

While portable fire extinguishers are an important means of early defense, it should be noted that there are certain situations were they might not be effective. For more information, see our archived article from September 2005 referencing fires involving vegetable based cooking oils.

Inspection of Extinguishers

Fire extinguishers shall be inspected when initially placed in service and thereafter at approximately 30-day intervals. The monthly inspections can be visual and are primarily to confirm that the units are not missing, are not blocked by storage or equipment and do not appear to be leaking or have a pressure loss. The monthly inspections should be recorded.


All extinguishers should be tested yearly. Items addressed include discharge valve operation, pressure gauge accuracy and ensuring that discharge nozzles are in satisfactory condition. Depending upon the Class of the extinguisher, addition testing and maintenance may be necessary. If the shell is damaged, a hydrostatic test may be needed.

Hydrostatic testing is needed every 5 or 12 years (depending of shell construction) regardless of the physical condition of the extinguisher.

Non-rechargeable fire extinguishers shall not be hydrostatically tested but shall be removed from service at a maximum interval of 12 years from the date of manufacture.


The above guidelines will hold in most occupancies. If your operations are considered high hazard, such as operations involving large quantities of flammable liquids or gases, or heavy metal working, we urge you to review the above referenced NFPA and FM Global publications.

Risk Logic can assist in determining the proper type of extinguisher for your operations.