Choosing the right fire extinguishers

Often times, someone in need of a fire extinguisher will purchase an ABC fire extinguisher without giving much thought to the actual fire hazards you need to protect against. When buying fire extinguishers, you need to know several things about fire extinguishers to make an informed decision, specifically, the class of fire to protect against and the special conditions to consider (computer electronics, for example).

Fire extinguisher classes

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 trash can and firewood. These extinguishers are used to put out fires in common fuels such as paper, cloth, rubber, and some plastics (materials that leave ash when burned, 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 flammable liquid fires such as 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 electrical outlet with a powered outlet. These fire extinguishers are used to extinguish electrical fires for energized electrical equipment, electrical motors, circuit boards, switches, and tools (“C” for electrical current).
• 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 fire extinguishers are used to extinguish metal fires and metal alloys such as titanium, sodium and magnesium.
• Class K – Class K fire extinguishers are specifically used for cooking grease, grease, and cooking oil (“K” for cooking) fires.

You can get fire extinguishers with a single class rating or with ratings of various fire classes (ABC or BC, for example).

Extinguishing materials

Fire extinguishers use different materials to extinguish fires. When choosing your extinguisher, you must determine what type of fire you may be fighting and then choose the best extinguisher material for your application.

• Water: Water extinguishers, or APWs, use pressurized water to extinguish fires. APW extinguishers can only be used for Class A fires (fuels such as paper, cloth, etc.); they cannot be used to put out other kinds of fires.
• Dry Chemical: Dry chemicals are used to extinguish Type A, B, C, or D fires. They work by putting a thin layer of chemical powder on the material that is burning. Dry chemical fire extinguishers are very effective at putting out fires. However, dry chemical extinguishers can be abrasive and corrosive to electronics and other materials.
• Carbon dioxide: Carbon dioxide works by removing oxygen from the vicinity of the fire. Carbon dioxide fire extinguishers are only used for B (flammable liquid) and C (electrical fires) fire extinguishers. For aviation computer, medical and scientific and electronic equipment, carbon dioxide would be a better choice than dry chemical fire extinguishers because a carbon dioxide fire 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 metal and metal alloy fires.

Special applications

Some fire hazards require specialized fire extinguishers. Here are some examples of those applications.

Metal or sand extinguishers are used to put out Class D fires (metals and metal alloys):

• Salt (sodium chloride – NaCl) is the most widely used material in metal / sand fire extinguishers. NaCl extinguishers work well on fires involving magnesium, sodium, potassium, sodium and potassium alloys, uranium, and powdered aluminum.
• Sodium carbonate extinguishers are also used on fires involving sodium, potassium, and potassium-sodium alloys. When considering the stress corrosion of stainless steel, this type of fire extinguisher would be a better choice than a NaCl extinguisher.
• Copper metal (Cu) powder is used for fires involving lithium and lithium alloys.
• Graphite powder extinguishers are used on lithium fires, as well as fires involving high-melting point metals such as titanium and zirconium.
• Baking soda-based fire extinguishers are used on fires involving metal alkyls and pyrophoric liquids.

Halotron I is a clean agent that replaces Halon 1211, the use of which was banned due to its ozone-depleting properties. Halotron I fire extinguishers are used to extinguish fires in computer rooms, clean rooms, and where telecommunications or electronic equipment is present. Halotron is residue-free and non-conductive, but it 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 that replaces Halon 1211. FE-36 extinguishers are less toxic than Halon 1211 and Halotron I and are reported to have no ozone depletion potential. FE-36 is also used for fires in computer rooms, clean rooms, and where telecommunications or electronic equipment is present. Unlike Halotron I, the FE-36 is not intended for disposal.

Non-Magnetic Fire Extinguishers – Whenever strong magnets are used, for example near Magnetic Resonance (MRI) or Nuclear Magnetic Resonance (NMRS) spectrometers, non-magnetic fire extinguishers should be chosen. The strong magnetic fields generated by this type of equipment can cause steel cylinder fire extinguishers to fly through a room with lethal force.

It is important to ensure you have the correct fire extinguishers for your environment or potential fire hazards. It can be the difference between whether your fire is eliminated or causes a catastrophe.