Often, someone who needs a fire extinguisher will buy an ABC fire extinguisher without giving much thought to the actual fire hazards they need to protect against. When buying fire extinguishers, you need to know several things about extinguishers in order to make an informed decision, specifically, the fire class you need to protect against and special conditions you need to consider (computer electronics, for example).
Classes of fire extinguishers
When it comes to fire extinguishers, there are five classes of fires: A, B, C, D, and K.
- Class A – Fire extinguishers rated for Class A fires have a green triangle with an “A” in the center as well as a pictogram of a garbage can and wood burning. These extinguishers are used to put out fires for common combustibles like paper, cloth, rubber, and some plastics (materials that leave ash when burnt, hence, the “A”).
- Class B – Fire extinguishers rated for Class B fires have a red square with a “B” in the center as well as a pictogram of a gasoline can with a burning puddle. These extinguishers are used to extinguish fires for flammable liquids like gasoline, lubricating oil, diesel fuel, and many organic solvents found in laboratories (things found in barrels, hence “B”).
- Class C – Fire extinguishers rated for Class C fires have a blue circle with a “C” in the center as well as a pictogram of an electric plug with a burning outlet. These extinguishers are used to extinguish electrical fires for energized electrical equipment, electric motors, circuit panels, switches, and tools (“C” for current-electrical).
- Class D – Fire extinguishers rated for Class D fires have a yellow pentagram (star) with a “D” in the center as well as a pictogram of a burning gear and bearing. These extinguishers are used to extinguish fires from metals and metal alloys like titanium, sodium, and magnesium.
- Class K – Class K fire extinguishers are used specifically for cooking fires from grease, fat, and cooking oil (“K” for kitchen).
You can get fire extinguishers with a single class rating or multiple fire class ratings (ABC or BC, for example).
Fire extinguishing materials
Fire extinguishers use different materials for extinguishing fires. When choosing your extinguisher, you need to determine what type of fire you may be fighting and then choose the best extinguishing material for your application.
- Water: Water, or APW, extinguishers use pressurized water to extinguish fires. APW extinguishers can only be used for Class A fires (combustibles such as paper, cloth, etc.); they cannot be used for putting out other classes of fires.
- Dry chemical: Dry chemicals are used to extinguish A-, B-, C-, or D-type fires. They work by putting a fine layer of chemical dust on the material that is burning. Dry chemical extinguishers are very effective at putting out fires. However, dry chemical extinguishers can be abrasive and corrosive to electronics and certain other materials.
- Carbon dioxide: Carbon dioxide works by removing oxygen from the immediate vicinity of the fire. Carbon dioxide extinguishers are only ever used for B (flammable liquid) and C (electrical fires) extinguishers. For computer, medical and scientific equipment, and aircraft electronics, carbon dioxide would be a better choice than dry chemical extinguishers because a carbon dioxide extinguisher leaves no residue.
- Metal/sand: Some class D fire extinguishers use metal or sand, such as sodium chloride (NaCl) or powdered copper metal, to smother fires from metals and metal alloys.
Special applications
Some fire hazards require specialized extinguishers. Here are a few examples of those applications.
Metal or sand extinguishers are used to put out class D (metal and metal alloy) fires:
- Salt (sodium chloride–NaCl) is the most commonly used material in metal/sand extinguishers. NaCl extinguishers work well with fires involving magnesium, sodium, potassium, alloys of potassium and sodium, uranium, and powdered aluminum.
- Sodium carbonate extinguishers are also used on fires involving sodium, potassium, and alloys of potassium and sodium. Where stress corrosion of stainless steel is a consideration, this type of fire extinguisher would be a better choice than an NaCl extinguisher.
- Powdered copper (Cu) metal is used for fires involving lithium and lithium alloys.
- Graphite powder extinguishers are used on lithium fires as well as fires that involve high-melting-point metals like titanium and zirconium.
- Sodium-bicarbonate-based extinguishers are used on fires involving metal alkyls and pyrophoric liquids.
Halotron I is a clean agent replacement for Halon 1211, which was banned from use due to its ozone depleting properties. Halotron I extinguishers are used for extinguishing fires in computer rooms, clean rooms, and where telecommunications equipment or electronics are present. Halotron leaves no residue and is nonconducting but is more expensive than carbon dioxide. It should be noted that Halotron I will no longer be produced after 2015.
FE-36 (CleanGuard) extinguishers are another clean agent replacement for Halon 1211. FE-36 extinguishers are less toxic than Halon 1211 and Halotron I and reportedly have no ozone-depleting potential. FE-36 is also used for fires in computer rooms, clean rooms, and where telecommunications equipment or electronics are present. Unlike Halotron I, FE-36 is not planned for phase-out.
Nonmagnetic fire extinguishers: Wherever strong magnets are in use, for example, near magnetic resonance imaging (MRI) or nuclear magnetic resonance spectrometers (NMRSs), nonmagnetic fire extinguishers should be chosen. The strong magnetic fields generated by this type of equipment can cause steel cylinder fire extinguishers to fly across a room with deadly force.
It is important to ensure that you have the proper fire extinguishers for your environment or potential fire dangers. It can be the difference between whether your fire is eliminated or causes a catastrophy.
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