The class and the size of fire likely to occur in a particular area are key factors in determining the appropriate type and size of extinguisher to be used. Together, the class and the size of a potential fire define the hazard for which your extinguisher installations must be designed.

Hazard Classification: (as per the National Fire Protection Association Standard for Portable Fire Extinguishers):

Light (Low) Hazard

Light (Low) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustibles and Class B flammables are low and fires with relatively low rates of heat release are expected.

Ordinary (Moderate) Hazard

Ordinary (Moderate) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustible materials and Class B flammables are moderate and fires with moderate rates of heat release are expected.

Extra (High) Hazard

Extra (High) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustible materialsare high or where high amounts of Class B flammables are present and rapidly developing fires with high rates of heat release are expected.

It is important to properly determine the hazard level for all areas. You may be required to install multiple extinguishers or extinguishers with multiple ratings. Restaurants, for example, require multiple extinguishers due to multiple hazards. Low hazards in dining areas would require a Class A extinguisher and high hazards in the kitchen would require a Class K extinguisher.

Special considerations have to be made for Class B fires.

There are four typical types of flammable liquid fires:

• Fire involving liquids at least 1/4″ deep
• Spill fires in which the burning liquid is less than 1/4″ deep
• Fires in which the burning liquid or gas is under pressure
• Three dimensional fires, involving burning liquids that are in motion

 

Deep liquid fires build up more heat than spill fires and are best extinguished with agents that smother the fire such as foam. Spill fires can be brought under control with carbon-di-oxide or dry chemical extinguishers. Gas under pressure can only be controlled with dry chemical. Extinguishers used for fighting pressurized Class B fires must be outfitted with a special nozzle, which allows for the rapid release of the drier chemical. These extinguishers are known as fast flow extinguishers.