The ABC’s (D and K) of Fire Extinguishers

You might think that a fire extinguisher is — well — a fire extinguisher, but there’s more to this than the surface level. Portable fire extinguishers are classified by the type of fires they are designed to extinguish. There are five basic classifications of fuel and extinguishers. Extinguishers are labeled with either letter-shaped or pictorial symbols that indicate how they’re intended to be used. 

It might be helpful to know that most portable extinguishers are rated for use with more than one classification of fire.  I will discuss this in more detail after we look at the basics:

Class A – Ordinary Combustibles (Use the word ASH as a reminder)
Class A fires involve common household materials, such as cloth, wood, paper, rubber, and many plastics. Extinguishers with an A rating are designed to extinguish fires resulting from these types of substances.  An A only rated fire extinguisher is just water under air pressure to extinguish the fire.  

Note: Never use water to extinguish flammable liquid or electrical fires.

Class B – Flammable Liquids (Use the word BOIL as a reminder)
Class B fires are associated with flammable and combustible liquids such as gasoline, alcohol, oil-based paints, and lacquers. To that end, extinguishers with a B rating are meant to address fires involving flammable and combustible liquids as well as flammable glasses.

Note: Do not attempt to put out a fire involving flammable gas unless you know definitively that the fuel can be promptly shut off. In fact, if the only fuel burning is the leaking gas, then the best approach is to shut off the fuel supply. Extinguishing a flammable gas fire, without shutting off the fuel, can prove disastrous. That’s because this move will allow unburned gas to escape into the atmosphere, which may permit a dangerous accumulation of gas to develop. An explosion may occur if that gas is exposed to an ignition source.

Class C – Electrical (Use the word CONDUCT as a reminder)
Class C fires usually result from energized electrical equipment. That means extinguishers with a C rating are designed for use with fires involving energized electrical equipment.  

Note: Unless you are clear that there is no energized electrical equipment in or around the fire, you must have a Class C rated fire extinguisher.

Class D – Combustible Metals
Class D fires are associated with combustible metals, such as magnesium, titanium, and sodium. Extinguishers with a D rating are designed to extinguish fires resulting from these sources.

Note: Common extinguishing agents may interact with a combustible metal fire, making the incident worse. The go-to method for extinguishing a combustible metal fire is to cover the burning material with a dry powder, such as sand, which will not react with the material. If you store or use combustible metals, make sure you have policies and procedures in place regarding the proper type and amount of extinguishing agent you should have on hand.  If you only store small quantities of combustible metals, it may be best, if allowed in your jurisdiction, to store them in an area where they cannot find an ignition source and they cannot cause damage to valuable property (a shipping container of their own).  In this case, you could state in your Emergency Action Plan that you will not address these fires and that employees should evacuate the area and notify the fire department in case of fire.

Class K – High Temp Cooking Fires (Use the word KITCHEN as a reminder)
Class K fires can be sparked by lipids, including vegetable oils, animal oils, or fats in cooking appliances. Extinguishers with a K rating are designed to extinguish fires related to cooking accidents in restaurants and cafeterias.  These extinguishers are intended to reduce the possibility of splashing the grease out of the fryers and to cover the surface with a soapy foam to eliminate the oxygen.

Multipurpose Extinguishers

The most common extinguishers are ABC rated and are suitable for use on fires involving both ordinary combustibles and flammable liquids. They are also safe to use around energized electrical equipment. 

Another common multipurpose extinguisher is a Carbon Dioxide extinguisher.  Noted by its large horn, it propels carbon dioxide gas toward the fire to cool it and exclude oxygen.  This BC rated extinguisher may be found in electrical rooms or hydraulic rooms where there are no ordinary combustibles.

Always know what type of fires you may face in your workplace and what type of extinguishers are available – BEFORE THE FIRE STARTS!

I’m always eager to extinguish your fire safety concerns.  Please reach out if you think you have unaddressed fire safety issues in your workplace.

Yours in fire safety,
Kenn

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