May 12, 2010

You do your monthly inspections to ensure your fire extinguishers are in place, in good shape, and accessible. But are you sure the fire extinguisher you're inspecting is actually the one you need? The fire extinguishers in your workplace should reflect both the fire class you need to protect against and the special conditions in the work area where they are located.

There are five classes of fire extinguishers:

• Class A extinguishers are for fires resulting from common combustibles like paper, cloth, rubber, and some plastics.
• Class B extinguishers are for fires resulting from flammable liquids like gasoline, lubricating oil, diesel fuel, and many organic solvents found in laboratories.
• Class C extinguishers are for fires resulting from energized electrical equipment, electric motors, circuit panels, switches, and tools.
• Class D extinguishers are for fires resulting from metals and metal alloys like titanium, sodium, and magnesium.
• Class K extinguishers are used specifically for cooking fires from grease, fat, and cooking oil.

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Within these extinguisher classes, fire extinguishers can use different materials for extinguishing fires. When choosing an extinguisher, you should consider both the class of fire the extinguisher is rated for and the material it uses to extinguish.

• Water: Water, or APW, extinguishers use pressurized water to extinguish fires. APW extinguishers are used only for Class A fires—never other classes of fires as they can exacerbate them.
• Dry chemical: Dry chemicals are used to extinguish Class A, B, C, or D fires. While very effective at putting out fires, dry chemical extinguishers can be abrasive and corrosive to electronics and certain other materials.
• Carbon dioxide: Carbon dioxide is used only in Class B and Class C extinguishers. For computer, medical, and scientific equipment, as well as aircraft electronics, carbon dioxide is generally a better choice than dry chemical extinguishers because carbon dioxide leaves no residue.
• Metal/sand: Some Class D fire extinguishers use metal or sand to smother fires from metals and metal alloys.
• Sodium chloride (NaCl) is the most commonly used material in metal/sand extinguishers. NaCl extinguishers work well on 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, sodium carbonate is generally 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.
• Specialty extinguishers: Some fire hazards require specialized extinguishers.
• 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. Halotron I will no longer be produced after 2015.
• FE-36 (CleanGuard) extinguishers use a clean-agent replacement that is less toxic than other clean-agent (Halon, Halotron) extinguishing materials and reportedly has no ozone-depleting potential. FE-36 is used for fires in computer rooms, clean rooms, and where telecommunications equipment or electronics are present.
• Nonmagnetic fire extinguishers: Wherever strong magnets are in use—for example, near magnetic resonance imaging (MRI) or nuclear magnetic resonance spectrometers (NMRs)—nonmagnetic fire extinguishers are the right choice. The strong magnetic fields generated by this type of equipment can cause steel cylinder fire extinguishers to fly across a room with deadly force.

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Planning for an Emergency Can Mean the Difference ...

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