What do the fire extinguisher classes A, B, C, D, and K mean?

Short answer: Fire extinguisher classes match an extinguisher to the kind of fuel that is burning: Class A is ordinary combustibles, Class B is flammable liquids, Class C is energized electrical, Class D is combustible metals, and Class K is cooking oils. NFPA 10 sets the classification and OSHA 29 CFR 1910.157 requires employers to select and distribute extinguishers by hazard. Using the wrong class — water on a grease or electrical fire — can make the fire worse.

Fire extinguisher classes explained: A, B, C, D, and K (2026 Guide)

Every portable fire extinguisher is built and rated to fight specific fuels, and the letter classes printed on the label are the key to matching the unit to the hazard. The classification system comes from NFPA 10, Standard for Portable Fire Extinguishers, and OSHA 29 CFR 1910.157 makes employers responsible for selecting, mounting, and maintaining extinguishers based on the fire classes present in each work area. Get the fire extinguisher class wrong and the consequences are immediate: water conducts electricity, and a stream of water hitting burning cooking oil can erupt into a fireball.

This guide decodes all five fire extinguisher classes, explains the numerical ratings that appear in front of the A and B letters, and shows how the agent inside the cylinder determines which classes it can fight. Whether you are equipping an ABC dry-chemical extinguisher for a shop or a Class K extinguisher for a commercial kitchen, the class is the first decision you make.

Why this matters.
Choosing the wrong fire extinguisher class is not a paperwork error — it is a flash-fire risk. Discharging a water or standard ABC unit onto a Class K cooking-oil fire can splash burning grease and spread the fire, which is why commercial kitchens are required to carry wet-chemical Class K units. OSHA cites employers under 29 CFR 1910.157 when extinguishers are missing, mismatched to the hazard, or unmaintained, and the National Fire Protection Association reports that cooking equipment is the leading cause of structure fires.

Part 1 — What the fire extinguisher classes mean

Fires are grouped by fuel because each fuel reacts differently to an extinguishing agent. The five U.S. classes under NFPA 10 are A, B, C, D, and K. An extinguisher may be rated for one class or several — a typical home or shop unit is rated A, B, and C — and the rated classes are shown as letters and pictographs on the nameplate.

Class A — ordinary combustibles

Class A covers wood, paper, cloth, cardboard, trash, and most plastics. These fires are extinguished primarily by cooling with water or by smothering. Class A is the only class that carries a water-based rating tied to the cylinder's effective water content.

Class B — flammable liquids and gases

Class B covers gasoline, diesel, oil, grease, solvents, paints, and flammable gases. Water is ineffective and often dangerous on Class B fuels because it spreads the liquid. Class B agents work by smothering or interrupting the chemical chain reaction.

Class C — energized electrical equipment

Class C is any fire involving energized electrical equipment — panels, motors, wiring, and appliances. The agent must be non-conductive. Once power is removed, the fire usually reverts to a Class A or B fire.

Class D and Class K

Class D covers combustible metals such as magnesium, titanium, sodium, and lithium, and requires a specialized dry-powder agent. Class K covers cooking oils and animal/vegetable fats in commercial kitchens and uses a wet-chemical agent that saponifies the oil to smother it.

Source: NFPA 10, Standard for Portable Fire Extinguishers. Class C/D/K carry no numerical rating.

Part 2 — How to read the rating on the label

The letters tell you which fires a unit fights; the numbers tell you how much. A rating like 2-A:10-B:C packs three pieces of information into one line. Only Class A and Class B carry numbers — C, D, and K are letter-only because their effectiveness is about the agent, not a measured capacity.

The A number

The number before the A indicates relative Class A extinguishing capacity. Each unit of A is roughly equivalent to 1.25 gallons of water, so a 2-A unit has about the effective capacity of 2.5 gallons of water on ordinary combustibles.

The B number

The number before the B approximates the square footage of a flammable-liquid fire that a trained non-expert can extinguish — a 10-B rating corresponds to roughly 10 square feet. A higher B number means more flammable-liquid coverage.

Part 3 — How the agent decides the class

What is inside the cylinder determines the classes it is rated for. Matching agent to hazard is the practical core of NFPA 10 selection.

Multipurpose vs. ordinary dry chemical

Monoammonium-phosphate dry chemical is the multipurpose ABC agent rated for A, B, and C. Sodium- or potassium-bicarbonate dry chemical is rated B and C only. ABC powder is mildly corrosive, which is why server rooms and labs often prefer clean agents or CO2.

CO2, water, wet chemical, and dry powder

Carbon dioxide is rated B and C and leaves no residue. Plain water and water-based units are Class A only. Wet chemical is the Class K kitchen agent. Class D fires require a specific dry-powder agent matched to the metal.

Part 4 — Matching the class to the space

Most general workplaces and homes are covered by a multipurpose ABC unit, but specific hazards demand specific classes. A welding shop with magnesium needs Class D on hand; a restaurant line needs Class K next to the cooking equipment in addition to ABC coverage elsewhere; a paint-mixing room is a Class B priority. Stock a rechargeable extinguisher where reuse and annual service make sense, and consider an extinguisher cabinet to protect and mark the unit in public spaces.

Part 5 — Using an extinguisher safely (the PASS method)

Even the correct class is only useful if it is discharged correctly and early. The PASS method — Pull, Aim, Squeeze, Sweep — is the standard discharge technique. Fight only small, incipient-stage fires with a clear exit behind you; if the fire is spreading, the room is filling with smoke, or you are unsure of the class, evacuate and call the fire department instead.

Part 6 — Common dangerous mismatches

The classes exist precisely because some agent-fuel combinations are hazardous. Never use water or a standard ABC unit on a Class K grease fire, never use water on a Class C electrical fire, and never use a water or ABC unit on burning combustible metal. When in doubt about an electrical fire, de-energize the equipment first if it is safe to do so, which converts it to an ordinary fire.

Part 7 — Worked example: equipping a home workshop and kitchen

Here is how the fire extinguisher classes drive a real buying decision for a household with an attached garage workshop and a kitchen, using units stocked on this site:

1. Identify the fire classes in each space. The workshop has ordinary combustibles (Class A), fuels and solvents (Class B), and energized power tools and chargers (Class C). The kitchen adds cooking-oil risk (Class K). That maps to ABC coverage everywhere plus a dedicated kitchen unit.
2. Choose a multipurpose ABC unit for general coverage. A rechargeable First Alert HOME2PRO 2-A:10-B:C rechargeable extinguisher covers the workshop's A, B, and C hazards. Browse the full ABC dry-chemical extinguisher range to size up or down.
3. Add a dedicated kitchen unit. Mount a kitchen-rated unit such as the Kidde 711A kitchen fire extinguisher near (but not directly over) the range. For commercial cooking volumes, step up to a Class K extinguisher.
4. Mount each unit on a clear escape path. Place extinguishers near exits so you are never trapped behind the fire to reach one. An extinguisher cabinet protects and marks the unit in shared spaces.
5. Train everyone on PASS and limits. Pull the pin, Aim at the base of the flames, Squeeze the handle, and Sweep side to side. Fight only small fires with a clear exit; otherwise evacuate and call 911.

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The same class-first logic scales from a single home to a multi-building facility. Start from the fire extinguishers catalog and the best fire extinguishers guide to match each rated class to the hazards you actually have.

Frequently asked questions

What are the 5 fire extinguisher classes?

The five U.S. fire extinguisher classes are Class A (ordinary combustibles), Class B (flammable liquids and gases), Class C (energized electrical equipment), Class D (combustible metals), and Class K (cooking oils and fats). They are defined by NFPA 10 and matched to hazards under OSHA 29 CFR 1910.157. Most general spaces are covered by a multipurpose ABC dry-chemical extinguisher.

What does ABC mean on a fire extinguisher?

An ABC fire extinguisher is rated to fight Class A, B, and C fires using a monoammonium-phosphate dry-chemical agent. It is the most common multipurpose unit for homes, offices, and shops because it handles ordinary combustibles, flammable liquids, and energized electrical equipment. See the full ABC extinguisher range.

Can you use water on a grease fire?

No. Water on a burning cooking-oil (Class K) or flammable-liquid (Class B) fire can violently splatter and spread the fire. Cooking-oil fires require a wet-chemical Class K extinguisher that smothers and cools the oil. For a small pan fire, smothering with a lid is safer than water.

What is the difference between Class B and Class K?

Class B covers flammable liquids broadly — gasoline, solvents, and oils — while Class K is a specialized class for cooking oils and fats in kitchens. Class K wet-chemical agents saponify hot oil to form a smothering layer and cool it below its auto-ignition point, which standard Class B agents do not do as effectively at cooking temperatures.

What does 2-A:10-B:C mean?

It is the rating line: 2-A indicates Class A capacity of about 2.5 gallons of water equivalent, 10-B indicates a flammable-liquid fire of roughly 10 square feet a trained user can extinguish, and C confirms the agent is safe on energized electrical equipment. Class C carries no number because it only signifies non-conductivity.

Which fire extinguisher is best for electrical fires?

Use a Class C-rated extinguisher with a non-conductive agent — a multipurpose ABC dry chemical or a CO2 unit. CO2 is popular around electronics because it leaves no residue. If it is safe, de-energizing the equipment first turns a Class C fire into an ordinary Class A or B fire.

Do I need a Class D fire extinguisher?

Only if you work with combustible metals such as magnesium, titanium, sodium, or lithium — common in foundries, machine shops, and some battery operations. Class D requires a specific dry-powder agent matched to the metal; a standard ABC unit can react dangerously with burning metal.

What is the PASS method?

PASS stands for Pull the pin, Aim at the base of the fire, Squeeze the handle, and Sweep side to side. It is the standard technique for discharging a portable extinguisher. Only use it on small, incipient-stage fires with a clear escape route behind you.

How big of a fire should I try to fight?

Only an incipient-stage fire — roughly the size of a wastebasket — with a clear exit at your back and the correct class of extinguisher in hand. A spray such as the First Alert EZ Fire Spray can knock down a very small fire, but if the fire is spreading or the room is filling with smoke, evacuate immediately and call the fire department.

What extinguisher should a kitchen have?

A commercial kitchen needs a wet-chemical Class K extinguisher by the cooking line, in addition to ABC coverage elsewhere. A home kitchen is well served by a small multipurpose unit like a Kidde 711A mounted near, but not over, the stove.

What fire extinguisher do I need for a car or garage?

A compact multipurpose ABC or BC unit handles the fuel and electrical hazards in a vehicle or garage. Look for a securely mountable unit rated for Class B and C at minimum — for example the Kidde FA110G multipurpose ABC extinguisher or an amzboom 4-pack with mounting brackets for multiple vehicles.

Why are some extinguisher classes letter-only with no number?

Class C, D, and K do not carry numerical ratings because their performance is about the agent's suitability, not a measured fire size. The C only certifies non-conductivity; D and K certify the agent is correct for metals or cooking oils. Only Class A and Class B capacities are quantified with a number.

Is an ABC extinguisher safe for everything?

An ABC unit covers the most common fires but is not universal. It should not be the primary unit for a commercial cooking-oil (Class K) fire or a combustible-metal (Class D) fire, and its dry-chemical residue is corrosive to electronics. Match the rated class to the actual hazard rather than assuming ABC is enough.

What does OSHA require for fire extinguishers?

OSHA 29 CFR 1910.157 requires employers to provide, mount, identify, and maintain portable extinguishers selected by the fire classes present, keep them accessible, and arrange annual maintenance and inspections. The detailed selection and distribution rules reference NFPA 10. See our OSHA 1910.157 guide.

How often should a fire extinguisher be inspected?

Portable extinguishers require a quick visual check monthly and a thorough maintenance inspection annually, with internal examination and hydrostatic testing on the schedule in NFPA 10. Check the pressure gauge, pin, and seal monthly and tag the annual service. Rechargeable units are serviced rather than replaced after use.

Where should fire extinguishers be mounted?

Extinguishers should be mounted on a clear escape path, near exits, and within the travel distances set by NFPA 10 — generally no more than 75 feet to a Class A unit and 30 to 50 feet to a Class B unit, depending on rating. Keep them visible, unobstructed, and at a height anyone can lift safely.

Further reading on this site

• Fire extinguishers — the full catalog across every rated class.
• ABC dry-chemical extinguishers — multipurpose A:B:C units for general workplaces and homes.
• Class K kitchen extinguishers — wet-chemical units for cooking-oil fires.
• Rechargeable extinguishers — refillable units worth servicing annually.
• Best fire extinguishers (2026) — editor picks by use case and rated class.
• OSHA 1910.157 explained — the employer requirements for portable fire extinguishers.
• OSHA flammable cabinet requirements — storing the Class B fuels that drive extinguisher selection.
• First Alert HOME1 rechargeable extinguisher — a compact 1-A:10-B:C unit for apartments and small spaces.
• Kidde 3-A:40-B:C high-capacity extinguisher — more reach and capacity for garages and workshops.
• OSHA 1910.132 PPE requirements — the general PPE rule that frames hazard assessment.
• Best smoke detectors (2026) — pair early detection with the right extinguisher class.