Equipment
Fire Extinguisher Classes A, B, C, D and K
Extinguisher classes describe the kind of fire the agent is rated to fight. Getting this wrong is not a technicality — using the wrong agent can spread a fire, splash burning liquid, or conduct electricity back to whoever is holding the extinguisher.
The five classes
| Class | Rated for |
|---|---|
| A | Ordinary combustibles — wood, paper, cloth, most plastics |
| B | Flammable liquids and gases — fuel, solvents, oil, paint |
| C | Energized electrical equipment |
| D | Combustible metals in specific industrial processes |
| K | Cooking oils and fats in commercial kitchens |
Most commercial buildings run multipurpose ABC dry chemical units, which cover the first three. The exceptions are where it gets important.
Where the exceptions matter
- Commercial kitchens need Class K at the cook line. Dry chemical on burning cooking oil can splash it.
- Server rooms and electrical spaces often want CO2 or a clean agent, because dry chemical residue destroys electronics it lands on.
- Auto shops, paint booths, and solvent handling need genuine Class B capacity, not a token ABC by the door.
- Class D is process-specific and rare. If you need it, you already know.
Using one: PASS
- Pull the pin.
- Aim at the base of the fire, not the flames.
- Squeeze the handle.
- Sweep side to side.
Before any of that: make sure someone has called 911, make sure you have an exit behind you, and be honest about size. A portable extinguisher is for a small fire. If it is bigger than a wastebasket, or if the room is filling with smoke, leave.
Common questions
Is an ABC extinguisher enough for a restaurant?
No. Commercial kitchens require Class K near the cook line. ABC units cover the rest of the building, but they are not appropriate for cooking oil fires.
What is the difference between Class B and Class K?
Both involve liquids, but cooking oils burn hotter and behave differently from fuels and solvents. Class K uses a wet chemical agent that reacts with hot oil to form a smothering layer. Class B agents do not do that.