Fires can occur only in the presence of adequate heat, oxygen, fuel (combustible material) and a chemical reaction, which is the actual fire. Portable fire extinguishers function by releasing an extinguishing agent intended to cool the fuel, remove or displace the oxygen, or stop the chemical reaction.
Selection and Location
The Universal Classification System (UCS) has five designations for fire extinguishers: class A, B, C, D and K. The classification is based on the type of material involved in the fire. Combination extinguishers are suitable for more than one class of fire and are marked with more than one classification letter. The most common multipurpose extinguisher, ABC, is suitable for most instances encountered by a farmer or gardener.
| Class | Symbol | Type of Fuel | Aid to Remember |
| A | Green Triangle | Ordinary combustibles | Things that make Ash |
| B | Red Square | Flammable liquids | Things that come in Barrels |
| C | Blue Circle | Electrical equipment | Things with a Charge |
| D | Yellow Star | Combustible metals | Things that Dent |
| K | Black Square | Cooking oils, fats and grease | Things in the Kitchen |
Locate fire extinguishers throughout the workplace. Be sure they are readily accessible and free of obstructions. OSHA-required spacing varies depending on the type of anticipated fire, but a good rule of thumb is to locate extinguishers at every exit and wherever potential fire hazards are great (welding or cutting areas, battery-charging stations, areas near open flames). Extinguishers should also be located on each vehicle or piece of equipment in the event a fire occurs in a location remote from nearby buildings. Extinguishers are available in different sizes, which typically correspond with the water equivalency (gallons) or the approximate area of coverage. Larger extinguishers last longer but can be bulky to use. Reference the manufacturer’s and the National Fire Protection Association (NFPA) ratings for specific sizing information.
Operating a Fire Extinguisher
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| Fire extinguisher operation. |
Call for help, as appropriate. Portable fire extinguishers can put out or control a fire until professional help arrives. The discharge time on most portable units is seconds only, so use portable units only on small fires or on fires in their initial stage. Plan an escape route. Stay low and avoid breathing smoke and the extinguishing agent. If the fire starts to spread or continues to burn when the extinguisher is empty, get out!
Remember the PASS acronym when fighting a fire, and follow these steps to operate an extinguisher:
• Pull the pin.
• Aim the fire extinguisher nozzle.
• Squeeze the handle to discharge the fire extinguisher contents.
• Sweep the spray back and forth at the base of the fire, not at the flames.
Inspection and Maintenance
While having a fire extinguisher of the correct type and size is important, knowing the extinguisher is ready to work when needed is also important. It may be necessary to visually inspect all units monthly to ensure good working condition (lack of vandalization), adequate protection and designated location. Fire safety standards require that all extinguishers be inspected annually by properly trained personnel. Inspection records must be available upon request.
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| Fire extinguisher inspection. |
Inspection Procedure
• Are all extinguishers in their recommended location?
• Is the tamper pin and seal intact?
• Have all dry chemical fire extinguishers been checked? To check a dry chemical fire extinguisher, remove it from its mounting bracket, invert it and tap the bottom with a rubber mallet to keep the dry chemical from caking.
• Does the gauge indicate enough pressure to discharge the contents? If not, replace or recharge the extinguisher as needed.
• Is the unit damaged?
• Are the hose and nozzle unobstructed?
References
• Fire Extinguishers. Quincy, MA: National Fire Protection Association. 2012.
• Evacuation Plans and Procedures: Portable Fire Extinguishers. Washington, DC: United States Department of Labor - OSHA, 2014.
osha.gov/SLTC/etools/evacuation/portable.html
Reviewer: Kent McGuire, CFAES Safety and Health Coordinator, Food, Agricultural and Biological Engineering