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The COMPLETE Guide To Fire Extinguishers | Fire Safety

The COMPLETE Guide To Fire Extinguishers | Fire Safety

Posted by Cale Myrick on Sep 11th 2019

Fire extinguishers.

We see them everywhere. They are often found in kitchens, on school buses, manufacturing facilities, and just about every other place of business you can think of. 

Those little (typically red) tubes of comfort, usually hanging on a wall by a metal bracket or either inside of an extinguisher case. 

But what IS a fire extinguisher really? You probably are thinking: "wow that's not a very smart question", but in reality, you'd be very surprised by the sheer amount of different fire extinguishers there are and how little the general public actually knows about them. 

Classes of fire extinguishers

Class A

Class A fire extinguishers are going to be your fire extinguishers that are found in most homes, apartments, and other living spaces. This is because Class A extinguishers are good for putting out fires that involve generally combustible materials. These items include plastic, cardboard, paper, wood, etc. The primary chemical used to fight these fires is Monoammonium Phosphate, because it smothers the fire in combustible materials. You will often see Class A extinguishers which utilize water instead of MAP, but these extinguishers can ONLY be used on Class A fires, because if used on a Class C fire it could create a shock hazard, and it could spread the flammable liquid in a class B fire.        


Fig-1. Standard Class A Extinguisher.

Note: some fire extinguishers are labeled "Class ABC", which indicates that an extinguisher can be used on class A,B, & C fires, which we will cover a little further into the article.

Class B

Class B fires involve flammable or combustible liquids. The most common flammable liquids include things like gasoline, grease, tars, oil-based paints, alcohols, solvents, etc. These fires are often the most common in places like refineries, plants, and other industrial work environments where employees are dealing with these flammable substances. The correct extinguisher type for a Class B fire is a Class B fire extinguisher, which can use dry chemicals to smother out the fires. While smothering out the fire can be an effective method of getting the flames out quickly, it tends to leave behind residue that can damage equipment & be a nightmare to clean up. For this reason, many companies have moved towards CO2, or Carbon Dioxide extinguishers for Class B fires as they are much cleaner after the fire has been eliminated.  


                                                                                                                                                         Fig-2. Standard Class B/C Extinguisher.

Note: grease fires in Class B are not to be confused with cooking fires, which now have their own classification known as Class K. This will be covered a little further into the article.

Class C

Class C fires are classified as electrical equipment fires. These are fires that burn in or on top of live electrical equipment. "Live" here simply means that the material that is on fire is energized, or fed by an electrical source of power. This could be caused from a wide range of things such as short circuits, bad wiring, damaged wiring, overloading circuits, etc. Water based extinguishers, and even those with water based foams, cannot and should not be used to attempt to put out a Class C fire. Class C fires are typically fought with Co2 fire extinguishers. It should go without saying that water and electricity do not mix, but in the panic mode of a fire, sometimes our thinking can be blurred. If a water based fire extinguisher is used on a Class C fire, you run the risk of actually spreading the fire, as water is an impeccable conductor for electricity. You also place the person holding the extinguisher at risk of fatal electrical shock. The first step in fighting an electrical, or Class C fire, is to cut off the power source to the equipment that is on fire. This means simply unplugging the device or equipment. Sometimes though, it is not a safe option, or with some industrial equipment, not immediately possible. Class C extinguishers are the only extinguishers that are suitable for fighting Class C electrical fires, as all other extinguishers are unsafe to do so. However, once you are 100% certain that the electricity has been removed from the situation, a Class A fire extinguisher can typically be used on whatever material or equipment is burning at the time since the electricity is no longer a factor.


                                                                                                                                                                       Fig-3. Standard Class C (Co2) Extinguisher. 

Note: grease fires in Class B are not to be confused with cooking fires, which now have their own classification known as Class K. This will be covered a little further into the article.

Class K

Class K fires are classified as fires that contain substances such as animal and vegetable fats. These are typically found in cooking oils and greases used in food preparation. While these are similar to SOME Class B fires, only a Class K extinguisher should be used to be sure the fire is disposed of properly and safely. Class K fires can grow rapidly due to the healthy fuel source of grease, oils, and fats found in most commercial kitchen settings. Class K extinguishers effectively deal with Class K fires using a wet mist that contains an alkaline mixture. This mist is applied to the fire and effectively quenches all steam and vapor from the fuel, putting out the fire and not allowing the fire to re-ignite. NEVER use a water based extinguisher on a grease fire, especially in your kitchen. If you didn't know, water will cause the oil or grease to splash, increasing the volatility of the fire, spreading it throughout the kitchen and making the fire that much more dangerous.

Check out this video to see what putting water on a grease fire looks like:


               Fig-4. Standard Class K Fire Extinguisher. 

Multipurpose Extinguishers

I am going to keep this one short and sweet. Multipurpose extinguishers, often known as "ABC fire extinguishers" are used for A,B, & C class fires. They are often the most ideal choice for an extinguisher because it leaves an individual or business prepared for a wide range of fire hazards, rather than forcing them to choose one. Class ABC fire extinguishers use monoammonium phosphate that is able to put out all three major classes of fires. Once again, this type of extinguisher will leave a residue that can damage surfaces and makes cleaning up after the fire that much harder, but it also leaves you prepared for whatever fire may occur.


                                                                                                                                                               Fig-5. Standard ABC/Multipurpose Fire Extinguisher.

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