Fire Extinguisher Classes: Complete Guide to Types A, B, C, D, and K

Using the wrong fire extinguisher can make a fire worse. I've seen homeowners spray water-based extinguishers on grease fires, turning a small pan flame into a kitchen-engulfing inferno. I've watched well-meaning employees blast electrical panels with foam, creating shock hazards on top of fire damage.

The five fire extinguisher classes exist for a reason: different fires require different solutions. Understanding these classes isn't just safety trivia—it's knowledge that could save your home, your workplace, or your life.

This guide covers each fire extinguisher class, what fires they handle, where you need them, and when a fire blanket might be the better choice. For a broader overview of fire safety equipment, check out our complete fire blanket guide.

Fire Extinguisher Classes at a Glance

Before diving into details, here's the quick reference you need:

Most homes need an ABC multi-purpose extinguisher plus a fire blanket for kitchen coverage. But understanding why each class exists helps you make smarter safety decisions.

Class A Fire Extinguisher: Ordinary Combustibles

Class A fires involve ordinary combustible materials—the stuff that burns in most typical fires. Think wood, paper, cloth, rubber, and many plastics. These are the fires you're most likely to encounter in daily life.

Where you need Class A protection:

• Homes and apartments
• Offices and schools
• Warehouses and storage facilities
• Retail stores

How Class A extinguishers work: They use water or water-based agents to cool the burning material below its ignition temperature. Once the material cools enough, combustion stops.

Common agents: Water, foam, and dry chemical compounds all work on Class A fires. Water extinguishers are cheap and effective but limited to Class A only.

Understanding the numbers: The number before "A" indicates extinguishing capacity. Each number equals 1.25 gallons of water equivalent. A 4A extinguisher provides the same firefighting capacity as 5 gallons of water.

For small Class A fires like a wastebasket or curtain, a fire blanket can also smother the flames effectively—and leaves no mess to clean up.

Class B Fire Extinguisher: Flammable Liquids

Class B fires involve flammable liquids and gases—gasoline, oil, grease, paint, solvents, propane, and similar materials. These fires burn hot and spread fast because the fuel can flow.

Where you need Class B protection:

• Garages and workshops
• Gas stations
• Paint shops and auto body facilities
• Industrial settings with solvents

Critical warning: Never use water on Class B fires. Water doesn't mix with oil—it sinks below the burning liquid, flash-boils into steam, and explosively spreads the burning fuel everywhere. I've seen small garage fires become infernos because someone grabbed a garden hose.

How Class B extinguishers work: They smother the fire by creating a barrier between the fuel and oxygen, or by interrupting the chemical reaction of combustion.

Common agents: CO2 (carbon dioxide), dry chemical, and foam. CO2 displaces oxygen and leaves no residue. Dry chemical interrupts the combustion reaction. Foam floats on burning liquids to smother them.

Understanding the numbers: The number before "B" indicates square footage coverage. A 10B extinguisher can handle a flammable liquid fire covering 10 square feet.

For grease fires specifically, a fire blanket is often faster and safer than an extinguisher. Learn more in our guide on how to put out a grease fire.

Class C Fire Extinguisher: Electrical Fires

Class C fires involve energized electrical equipment—anything plugged in or connected to power. The danger isn't just the fire; it's the electrocution risk from using the wrong extinguishing agent.

Where you need Class C protection:

• Server rooms and data centers
• Offices with computers and electronics
• Kitchens with appliances
• Manufacturing facilities

Critical rule: Never use water or foam on electrical fires. Water conducts electricity, creating a shock hazard that can kill you faster than the fire.

How Class C extinguishers work: They use non-conductive agents that won't transmit electricity back to you. Once you disconnect power, an electrical fire becomes a Class A or B fire (depending on what's burning).

Common agents: CO2 and dry chemical are both non-conductive and safe for electrical fires. CO2 is preferred for electronics because it leaves no residue that could damage sensitive equipment.

Pro tip: If possible, disconnect power before fighting the fire. An unplugged computer fire is just a plastic fire (Class A). Shutting off the breaker eliminates the electrical hazard.

Class C doesn't have a numerical rating because the classification only indicates the agent won't conduct electricity—it doesn't measure firefighting capacity.

Class D Fire Extinguisher: Combustible Metals

Class D fires involve combustible metals—magnesium, titanium, sodium, lithium, potassium, and their alloys. These fires are rare in homes but critical in industrial settings.

Where you need Class D protection:

• Machine shops and metal fabrication
• Aircraft manufacturing
• Laboratories
• Facilities working with powdered metals

Why metal fires are different: Combustible metals burn at extremely high temperatures and react violently with water, CO2, and most common extinguishing agents. Using the wrong extinguisher can cause explosions.

How Class D extinguishers work: They use specialized dry powder agents designed for specific metals. The powder smothers the fire and absorbs heat without reacting with the burning metal.

Important note: Different metals require different agents. A magnesium fire extinguisher may not work on a lithium fire. Facilities must match extinguishers to the specific metals they work with.

Lithium battery fires: With the rise of electric vehicles and lithium-ion batteries, Class D fires are becoming more relevant to everyday life. Our EV fire blanket is designed specifically for containing lithium battery fires in vehicles and e-bikes.

Class K Fire Extinguisher: Cooking Oils and Fats

Class K fires involve cooking oils and fats—vegetable oil, animal fats, and greases used in cooking. While technically a subset of Class B (flammable liquids), cooking oils behave differently and require specialized treatment.

Where you need Class K protection:

• Commercial restaurant kitchens
• Cafeterias and food service
• Any facility with deep fryers

Why cooking oils are special: Cooking oils have high auto-ignition temperatures and can re-flash (reignite) after apparently being extinguished. Standard Class B agents may not prevent re-ignition.

How Class K extinguishers work: They use wet chemical agents (typically potassium acetate or potassium carbonate) that react with cooking oils through a process called saponification—essentially turning the burning oil into soap. This creates a foam blanket that cools the oil and prevents oxygen contact.

For home kitchens: Most residential cooking fires don't require a Class K extinguisher. A fire blanket is often the better choice:

• Deploys in 3 seconds vs. fumbling with an extinguisher
• No training required
• Leaves no chemical residue to clean
• Won't splash burning oil like pressurized extinguishers can
• Works on grease, oil, and pan fires

For more on kitchen fire safety, see our comparison of fire blanket vs fire extinguisher.

ABC Fire Extinguisher: The Multi-Purpose Option

Most homes and businesses use ABC-rated extinguishers that handle Classes A, B, and C. These multi-purpose units represent about 80% of all fire extinguishers sold.

How ABC extinguishers work: They use dry chemical agents (typically monoammonium phosphate) that interrupt the chemical reaction of combustion and coat burning materials to prevent re-ignition.

Pros of ABC extinguishers:

• Versatile—handles most common fire types
• Widely available at hardware stores
• Affordable ($20-50 for home units)
• Good all-around protection

Cons of ABC extinguishers:

• Messy—the powder gets everywhere and is hard to clean
• Corrosive—can damage electronics and metal surfaces
• Doesn't cover Class K (cooking oils effectively)
• Can spread grease fires if aimed wrong

The smart combination: For complete home protection, keep an ABC extinguisher plus a fire blanket. The extinguisher handles larger fires and electrical hazards; the fire blanket handles quick kitchen fires without the mess. Learn more about building your safety kit in our fire safety guide.

How to Read Fire Extinguisher Labels and Ratings

Fire extinguisher labels use a number-letter system that tells you exactly what the unit can handle. Understanding this system helps you choose the right extinguisher for your needs.

Example rating: 2A:10B:C

• 2A = Handles Class A fires with capacity equal to 2.5 gallons of water (2 × 1.25)
• 10B = Handles Class B fires up to 10 square feet
• C = Safe for electrical fires (no number because it just indicates non-conductivity)

What the symbols mean:

• Green triangle with "A" = Ordinary combustibles (wood, paper)
• Red square with "B" = Flammable liquids
• Blue circle with "C" = Electrical equipment
• Yellow star with "D" = Combustible metals
• Black hexagon with "K" = Cooking oils/fats

Pictograms: Modern extinguishers also show pictures of fires they can and cannot fight. A red slash through a picture means "don't use on this type of fire."

UL listing: Always look for the "UL Listed" label, indicating the extinguisher meets Underwriters Laboratories safety standards. According to the U.S. Fire Administration, using UL-listed equipment is essential for reliable fire protection.

How to Use a Fire Extinguisher: The PASS Method

Having the right extinguisher means nothing if you don't know how to use it. The PASS method is the universal technique taught by fire departments worldwide.

P - Pull the pin

Break the tamper seal and pull the pin from the handle. This unlocks the operating lever.

A - Aim at the base

Point the nozzle at the base of the fire, not at the flames. The base is where the fuel is—that's what you need to extinguish.

S - Squeeze the lever

Squeeze the operating lever to discharge the agent. Release to stop the flow.

S - Sweep side to side

Sweep the nozzle from side to side, covering the entire base of the fire until flames are out.

Important considerations:

• Distance: Stand 6-10 feet from the fire (check your extinguisher's label for specific range)
• Duration: Most home extinguishers last only 10-25 seconds—use short bursts
• Escape route: Always keep your back to an exit so you can escape if the fire grows
• When to stop: If the fire doesn't respond within 30 seconds, evacuate immediately

The National Fire Protection Association recommends that only people trained in extinguisher use attempt to fight fires, and only when the fire is small and contained.

Fire Extinguisher vs Fire Blanket: When to Use Each

Fire extinguishers and fire blankets serve different purposes. Here's when each one shines:

The ideal setup: Most fire safety experts recommend having both. An ABC extinguisher gives you range and versatility for larger fires. A fire blanket gives you instant response for kitchen emergencies and leaves no chemical cleanup.

Fire blankets also work as a personal shield when escaping through smoke or flames—something extinguishers can't do.

Fire Extinguisher Maintenance: Keep It Ready

A fire extinguisher that doesn't work when you need it is worse than no extinguisher at all—it wastes precious seconds. Follow this maintenance schedule:

Monthly checks (do it yourself):

• Confirm extinguisher is in its designated location
• Check that the pressure gauge needle is in the green zone
• Verify the pin and tamper seal are intact
• Look for visible damage, rust, or leaks
• Ensure the label is readable

Annual inspection (professional):

• Certified technician checks all components
• Verifies proper pressure and charge
• Inspects hose and nozzle condition
• Adds inspection tag with date

6-year maintenance:

• Internal examination of rechargeable extinguishers
• Empty, inspect, and recharge

12-year hydrostatic test:

• Pressure test of the cylinder
• Required for rechargeable units
• Disposable extinguishers should be replaced at 12 years

Replace immediately if:

• Used (even partially)—always recharge or replace after any use
• Pressure gauge shows red (undercharged)
• Visible damage or corrosion
• Past expiration or hydrostatic test date

For more on equipment lifespan, see our article on when to replace a fire extinguisher.

Choosing the Right Fire Extinguisher for Your Needs

Here's what different spaces typically need:

Home/Apartment:

• Kitchen: Fire blanket + small ABC extinguisher
• Garage: 10+ lb ABC extinguisher
• Each floor: 5 lb ABC extinguisher near exits

Office/Business:

• General areas: ABC extinguishers every 75 feet
• Server room: CO2 extinguisher (protects electronics)
• Kitchen/break room: Fire blanket + Class K if deep fryer present

Workshop/Garage:

• ABC extinguisher for general fires
• BC extinguisher near fuel storage
• Fire blanket for welding/grinding areas

Vehicles:

• Car: Compact BC or ABC extinguisher
• EV/Hybrid: Fire blanket rated for lithium batteries
• Boat: Marine-rated BC extinguisher