Fire Extinguisher Classes: A, B, C, D & K Explained
Every fire is not the same — and neither is every extinguisher. This guide walks through the five classes recognized by NFPA 10, what fuels each one fights, and how to pick the right unit for your business.
Why the classes matter
Using the wrong extinguisher can make a fire worse — spraying water on a grease fire spreads burning oil; putting foam on live electrical gear can shock the user. NFPA 10 (the national standard for portable fire extinguishers) sorts fires into five classes so you can match the agent to the fuel. A single business often needs two or three different types.
Below is a plain-English breakdown of each class — the fuels it covers, the extinguishing agents that work on it, the pictogram you'll see on the label, and where you're most likely to need one.
Class A — Ordinary combustibles
- Fuels
- Wood, paper, cloth, rubber, most plastics, trash
- Extinguishing agent
- Water, foam, or multi-purpose dry chemical (ABC)
- Label pictogram
- Green triangle
- Common locations
- Offices, retail, schools, warehouses, apartment common areas
Class B — Flammable liquids & gases
- Fuels
- Gasoline, oil, grease, paint, solvents, propane
- Extinguishing agent
- Dry chemical (ABC or BC), CO₂, or foam
- Label pictogram
- Red square
- Common locations
- Auto shops, paint booths, fuel storage, manufacturing, generator rooms
Class C — Energized electrical equipment
- Fuels
- Panels, motors, appliances, computers, servers
- Extinguishing agent
- Non-conductive: CO₂ or dry chemical (ABC/BC)
- Label pictogram
- Blue circle
- Common locations
- Server rooms, electrical closets, data centers, workshops
Class D — Combustible metals
- Fuels
- Magnesium, titanium, sodium, potassium, lithium, aluminum shavings
- Extinguishing agent
- Dry powder (Class D only — never water)
- Label pictogram
- Yellow star
- Common locations
- Metal fabrication, machine shops, labs, battery manufacturing
Class K — Cooking oils & fats
- Fuels
- Vegetable oil, animal fat, deep-fryer grease
- Extinguishing agent
- Wet chemical (potassium acetate) — saponifies the oil
- Label pictogram
- Black hexagon
- Common locations
- Commercial kitchens, restaurants, food trucks (NFPA 96 required)
Picking the right extinguisher for your business
Most businesses don't need every class — but almost every business needs more than one. Here's how it usually breaks down:
- Offices, retail, and general commercial: multi-purpose ABC units cover most risks.
- Restaurants and commercial kitchens: ABC in the dining and back-of-house areas plus a Class K unit within 30 feet of the cooking line.
- Auto shops, warehouses with fuels or solvents: ABC plus dedicated Class B extinguishers near hazards.
- Server rooms, IT closets, electrical rooms: CO₂ (Class BC) is preferred — it leaves no residue on equipment.
- Machine shops handling magnesium, lithium, or other reactive metals: Class D dry-powder units near the hazard.
A Florida requirement worth knowing
Florida follows NFPA 10 for annual inspection and NFPA 96 for commercial cooking systems. Class K extinguishers, hood cleanings, and semiannual system checks are all required in restaurants — and fire marshals check tags. If you're unsure whether your setup passes, we'll walk your space and tell you exactly what's needed.
Frequently asked questions
What do the letters on a fire extinguisher mean?
The letters tell you what class of fire the extinguisher is rated to fight. A is ordinary combustibles (wood, paper), B is flammable liquids, C is energized electrical equipment, D is combustible metals, and K is cooking oils and fats.
What is an ABC fire extinguisher?
An ABC extinguisher uses multi-purpose dry chemical to fight Class A, B, and C fires. It's the most common general-purpose unit and covers the majority of hazards in offices, retail, and warehouses.
Do commercial kitchens really need a Class K extinguisher?
Yes. NFPA 10 and NFPA 96 require a Class K wet-chemical extinguisher wherever cooking appliances use vegetable or animal fats. An ABC alone is not compliant, and fire marshals will flag it.
Can I use water on an electrical fire?
No — water conducts electricity and can shock the user or spread the fire. Use a Class C-rated extinguisher (CO₂ or dry chemical) on energized electrical equipment. Once power is cut, the fire may effectively become Class A.
How many extinguishers does my business need?
NFPA 10 sets minimum coverage by square footage, hazard level, and travel distance to the nearest unit (generally no more than 75 feet). We do free walk-throughs to size it correctly.
Not sure which extinguishers you need?
We'll survey your space, check your existing units, and give you a written NFPA 10 compliance plan — no obligation.