Fire Extinguishers

Involves wood, paper, cloth, rubber, and most plastics. Extinguished by cooling (water) or coating (dry chemical, foam). Water is the most effective agent for Class A fires because it absorbs heat and penetrates burning material.

Involves gasoline, oil, grease, solvents, and flammable gases. Extinguished by smothering (CO₂, foam) or chemical chain reaction interruption (dry chemical). Never use water — it spreads burning liquid and can cause steam explosions.

Involves energized electrical equipment. The "C" rating confirms the agent is non-conductive — CO₂ and dry chemical are appropriate. Water conducts electricity and must never be used. Once equipment is de-energized, the fire becomes Class A or B.

Involves magnesium, titanium, sodium, potassium, and other combustible metals. Requires a specific dry powder agent matched to the metal present — no universal Class D agent exists. Water reacts violently with many combustible metals.

Involves cooking oils and fats in commercial kitchen equipment. Wet chemical agents saponify the oil, forming a soapy foam that seals the surface and prevents re-ignition. Required for commercial cooking equipment — dry chemical is not sufficient.

The number before "A" represents relative extinguishing capacity. A 1-A rating equals the extinguishing equivalent of 1.25 gallons of water. A 4-A extinguisher is four times as effective as a 1-A. Higher numbers indicate greater capacity.

The number before "B" represents the approximate square footage of a flammable liquid fire the extinguisher can control. A 10-B rating indicates effectiveness on approximately 10 square feet of flammable liquid fire.

The "C" rating carries no numerical value. It simply confirms the extinguishing agent is non-conductive and safe for use on energized electrical equipment. It does not indicate the size of electrical fire that can be controlled.

Class D extinguishers are rated for specific metals — the label identifies which metals the agent is effective against. Class K extinguishers are rated for commercial cooking equipment and must be matched to the specific cooking appliance.

Many extinguishers carry multi-class ratings (e.g., ABC dry chemical). A "2-A:10-B:C" unit handles ordinary combustibles, flammable liquids, and energized electrical equipment. Always verify the rating matches the hazards present in the area.

Extinguishers for Class A hazards must be located so that the maximum travel distance from any point in the protected area to the nearest extinguisher does not exceed 75 feet.

Extinguishers for Class B hazards must be within 50 feet of the hazard. The higher hazard potential of flammable liquids justifies the shorter travel distance requirement.

Class C extinguishers are placed based on the Class A or B hazard present — there is no independent travel distance for Class C. The requirement is that the agent selected must be non-conductive.

Class D extinguishers must be within 75 feet of the combustible metal hazard and must be matched to the specific metal present. A single extinguisher may not be appropriate if multiple different combustible metals are present.

Class K extinguishers must be located within 30 feet of commercial cooking equipment. The automatic suppression system in the hood must be activated before or simultaneously with extinguisher use.

Extinguishers weighing 40 lbs or less: top of handle no higher than 5 feet above the floor. Extinguishers over 40 lbs: top of handle no higher than 3.5 feet. Bottom of extinguisher must be at least 4 inches above the floor.

Pull the safety pin from the handle. This breaks the tamper seal and unlocks the operating lever. Without removing the pin, the extinguisher cannot be discharged.

Aim the nozzle, horn, or hose at the base of the fire — not at the flames. Directing the agent at the flames is ineffective; the agent must reach the fuel source to extinguish the fire.

Squeeze the operating lever to discharge the agent. Release the lever to stop discharge. Most extinguishers have a discharge time of 8–25 seconds depending on size and agent type.

Sweep the nozzle from side to side at the base of the fire, moving forward as the fire diminishes. Continue until the fire is completely out. Watch for re-ignition and be prepared to repeat.

Do not attempt to fight a fire if: the fire is larger than a small wastebasket, the room is filling with smoke, you do not have a clear exit behind you, you are not trained, or the fire involves unknown chemicals. In these cases, evacuate immediately and call 911.

Portable extinguishers are designed for incipient-stage fires — fires in their earliest stage before significant heat buildup. Once a fire has grown beyond incipient stage, the extinguisher will be ineffective and evacuation is the only safe option.

Remove anyone in immediate danger if it is safe to do so. In a hospital or clinic setting, this means moving patients away from the immediate fire area — rescue takes priority over fire suppression. Never enter a smoke-filled area without proper respiratory protection.

Activate the nearest manual pull station and call 911. Do not assume someone else has already called. Early alarm activation is critical to minimizing fire spread and ensuring emergency responder response time.

Close all doors and windows to slow the spread of fire and smoke. Closed doors can significantly delay fire spread and reduce smoke migration to adjacent areas, buying critical time for evacuation.

Attempt to extinguish only if the fire is small (incipient stage), you have a clear exit behind you, you are trained in extinguisher use, and the correct extinguisher is available. If any condition is not met, evacuate immediately.

Required monthly by a designated person. Check: extinguisher is in designated location, unobstructed and visible; operating instructions face outward; tamper seal and safety pin are intact; pressure gauge is in the operable range (green zone); no obvious physical damage, corrosion, or leakage.

Required annually by a qualified/certified person. Includes a thorough examination of mechanical parts, extinguishing agent, and expelling means. The maintenance tag must be updated with the date and technician identification. Defective units must be removed from service.

Hydrostatic testing is required every 5 or 12 years depending on extinguisher type, per OSHA 29 CFR 1910.157. The applicable intervals are listed in Table L-1 below.

OSHA 29 CFR 1910.157 Table L-1 — Hydrostatic Test Intervals

Stored-pressure dry chemical extinguishers require an internal examination every 6 years. The agent is emptied, the cylinder is inspected internally, and the unit is recharged. This is in addition to the 5-year hydrostatic test.

NFPA 10 requires records of all inspections, maintenance, and hydrostatic tests. Records must include the date, name of the person performing the work, and the result. Tags attached to the extinguisher serve as the primary record.

Water extinguishers are effective on Class A fires only. Water mist extinguishers use deionized water and are safe for Class C environments. Never use standard water extinguishers on Class B or C fires.

The most common type. Monoammonium phosphate agent is effective on Class A, B, and C fires. Leaves a corrosive residue that must be cleaned up promptly. Not suitable for Class D or K fires.

Effective on Class B and C fires. Leaves no residue — preferred for sensitive equipment. The CO₂ horn becomes extremely cold during discharge (dry ice formation). Limited effectiveness outdoors due to wind dispersal.

Specifically designed for Class K fires. The potassium acetate or potassium citrate agent reacts with hot cooking oil to form a soapy foam (saponification) that seals the surface and prevents re-ignition. Required for commercial cooking equipment.

Specific to Class D combustible metal fires. Common agents include sodium chloride (for sodium, potassium), graphite-based powder (for magnesium, titanium), and copper powder (for lithium). Must be matched to the specific metal.

FM-200 (HFC-227ea) and Novec 1230 are clean agents that suppress fire without leaving residue and are environmentally preferred over halon. Effective on Class B and C fires. Used primarily in fixed suppression systems for sensitive equipment.