Fire Extinguisher Types & Classes

Choosing the right fire extinguisher is not a preference — it is a code requirement matched to the specific fuel hazards present in a space. The wrong class can fail to extinguish a fire, spread it, or in some cases (like water on a grease fire) make it dramatically worse. This guide covers the five Canadian fire extinguisher classes, what each is rated for, where the codes require them, and how to make the correct selection for your venue or operation.

The Five Classes (NFPA 10)

Class A — Ordinary Combustibles

For fires involving wood, paper, fabric, plastic, rubber, and most general waste. Class A extinguishers use water, foam, or dry chemical agents that cool the fuel below ignition temperature. Most office, retail, and residential fires are Class A.

Common agents: Water (legacy), foam, ABC dry chemical, water mist.

Class B — Flammable Liquids and Gases

For fires involving gasoline, oil, paint, solvents, propane, butane, and other liquid or gaseous fuels. Class B agents work by smothering the fuel surface or interrupting the chemical chain reaction. Never use water on a Class B fire — water will scatter burning liquid and spread the fire.

Common agents: ABC dry chemical, BC dry chemical, CO2, foam, halotron.

Class C — Energized Electrical

For fires involving live electrical equipment, motors, transformers, panels, and energized circuits. The agent must be non-conductive — water and foam are dangerous on Class C because they conduct electricity back to the user. Once the power is cut, the fire becomes Class A or B depending on the surrounding fuel.

Common agents: ABC dry chemical, CO2, halotron, clean agent.

Class D — Combustible Metals

For fires involving magnesium, titanium, sodium, potassium, lithium, and other reactive metals. Class D fires burn at extreme temperatures and react violently with water, foam, and most chemical agents — a water-based extinguisher on a magnesium fire causes an explosive reaction. Class D agents are specialized dry powders (sodium chloride, copper, graphite-based) that smother the metal without reacting.

Common agents: Sodium chloride (Met-L-X), copper-based, graphite-based dry powders.

Where required: Industrial facilities working with reactive metals, lithium battery storage, EV manufacturing and charging hubs, machine shops handling magnesium or titanium parts.

Class K — Cooking Oils and Fats

For fires involving cooking oils, animal fats, and vegetable fats in commercial kitchen equipment — deep fryers, woks, griddles, and broilers. Class K agents use a wet chemical (potassium acetate, potassium citrate) that saponifies the burning oil, forming a soapy foam layer that cools and seals the surface.

Critical: ABC dry chemical does not extinguish Class K fires reliably — the high temperature of cooking oil (often above 360 °C) re-ignites once dry chemical settles. Canadian fire codes (Ontario Fire Code, RBQ Quebec, BC Fire Code) mandate Class K extinguishers in commercial kitchens with deep fryers or large cooking surfaces.

Common agents: Potassium acetate wet chemical (most common), potassium citrate wet chemical.

ULC Ratings — What the Numbers Mean

Canadian extinguishers carry ULC numerical ratings that indicate extinguishing capacity. A label reading 4A:80B:C means:

• •4A — Class A capacity equivalent to 4 imperial gallons of water (rough fuel-load rating)
• •80B — Class B capacity for an 80-square-foot flammable liquid fire
• •C — Tested non-conductive on energized electrical (no numerical rating; pass/fail)

Higher numbers = more capacity. A 5 lb ABC unit is typically rated 2A:10B:C; a 10 lb unit is 4A:80B:C; a 20 lb unit is 10A:120B:C. Code-required ratings depend on occupancy and hazard density — NFPA 10 specifies minimum ratings per square metre for each occupancy class.

Selection by Venue Type

Sizing — 5 lb vs 10 lb vs 20 lb

• •5 lb ABC — small offices, vehicles, residential, food trucks. Discharge time ~10 seconds; covers small early-stage fires.
• •10 lb ABC — standard commercial. Discharge ~18–22 seconds; rated 4A:80B:C; covers most code requirements for Class A and B.
• •20 lb ABC — industrial, large warehouses, high-hazard occupancies. Discharge ~25 seconds; rated 10A:120B:C.
• •Wheeled units (50–350 lb) — industrial yards, refineries, fuel depots. Required where fixed extinguishers cannot cover the hazard area.

What ABC Does Not Cover

ABC dry chemical is the most versatile single agent, but it has limits:

• •Class K (kitchen oils) — may suppress briefly but re-ignition is common
• •Class D (combustible metals) — reacts violently with most reactive metals
• •Sensitive electronics — dry chemical residue is corrosive and conductive once damp; CO2 or clean agent preferred
• •Cleanrooms, food-processing surfaces, art — dry chemical residue contamination requires extensive cleanup

Codes and Standards Referenced

• •NFPA 10 — Standard for Portable Fire Extinguishers (the primary technical standard adopted across Canada)
• •CAN/ULC-S503, S504, S507 — Canadian standards for extinguisher manufacture and testing
• •NBCC §2.8 / Provincial Fire Codes — occupancy-based requirements for placement, type, and rating
• •CAN/ULC-S536 — Inspection and testing standard
• •NFPA 96 — Standard for ventilation control and fire protection of commercial cooking operations (drives K-class requirements)

Need Help Choosing?

Most properties need a mix of types — ABC throughout for general coverage, K-class in any kitchen with cooking oil, CO2 near electrical panels and server rooms. Our partners conduct hazard assessments based on occupancy class, fuel load, and equipment, and provide a written placement plan that satisfies NFPA 10 and your provincial fire code.

Request a quote for fire extinguisher rental, inspection and tagging, or recharge service — we can recommend the correct types and quantities for your venue.