What Are the Five Fire Extinguisher Classes?

Fire extinguishers in the United States are classified according to the type of fuel involved in the fire.

These classifications help you match the extinguishing agent to the fuel involved. Using the wrong agent can be ineffective and, in some situations, can spread the fire or create an additional hazard.

Class A Fires: Wood, Paper, and Ordinary Combustibles

Class A fires involve materials commonly found in homes, offices, stores, and warehouses, including:

• Wood
• Paper and cardboard
• Fabric
• Trash
• Rubber
• Many plastics

Water-based extinguishers may be rated for Class A fires, while many multipurpose dry-chemical extinguishers are rated for Classes A, B, and C.

Class B Fires: Flammable Liquids and Gases

Class B fires involve substances such as:

• Gasoline
• Diesel fuel
• Paint thinner
• Solvents
• Alcohol
• Petroleum-based oils
• Propane and other flammable gases

These hazards are frequently found in garages, workshops, service facilities, factories, laboratories, and fuel-storage areas.

Class B fires require an agent that can interrupt combustion or separate the fuel from oxygen. Water can spread a burning flammable liquid and should not be used unless a specifically designed and approved system calls for it.

Class C Fires: Energized Electrical Equipment

Class C fires involve equipment that is still connected to an electrical power source, such as:

• Electrical panels
• Wiring
• Fuse boxes
• Computers and servers
• Appliances
• Power tools
• Industrial machinery

The “C” rating means the extinguishing agent is suitable for use where energized electrical equipment is involved.

Once the electrical power has been safely disconnected, the remaining fire may be treated according to the material that continues to burn. For example, burning plastic housing may become a Class A fire after the electrical hazard has been isolated.

Carbon dioxide extinguishers are commonly rated for Class B and C fires and leave no residue, which can be useful around sensitive electronic equipment. However, they have limitations, including a relatively short discharge range and reduced effectiveness in windy conditions.

Class D Fires: Combustible Metals

Class D fires involve combustible metals such as:

• Magnesium
• Titanium
• Sodium
• Potassium
• Zirconium
• Certain aluminum or metal powders

These are specialized industrial hazards. A standard ABC extinguisher should not be treated as a substitute for an extinguisher specifically designed for the metal involved.

The correct Class D agent depends on the combustible metal, its physical form, and the surrounding process. Facilities working with combustible metals should perform a formal hazard assessment and follow the applicable Safety Data Sheets, equipment instructions, and fire codes.

Class K Fires: Commercial Cooking Oils and Fats

Class K fires involve high-temperature cooking oils and fats, particularly in commercial cooking appliances such as deep fryers.

Wet-chemical Class K extinguishers are designed to cool the burning oil and create a barrier that helps prevent reignition. Applicable commercial kitchens generally require Class K protection in coordination with the installed hood and suppression system, subject to local requirements.

What Does an ABC Fire Extinguisher Mean?

An ABC fire extinguisher is rated for:

• Class A: ordinary combustibles
• Class B: flammable liquids
• Class C: energized electrical equipment

Because it covers several common hazards, an ABC extinguisher is frequently selected for homes, offices, garages, vehicles, and general commercial environments.

However, “multipurpose” does not mean “appropriate for everything.”

An ABC extinguisher is not automatically suitable for:

• Combustible-metal fires
• Commercial deep-fat fryer fires
• Every lithium-ion battery incident
• Every sensitive electronic environment
• Large or rapidly spreading fires

Always check the classification printed on the extinguisher label and confirm that the product is suitable for the hazards in the protected area.

For the U.S. market, look for products evaluated and labeled by an appropriate nationally recognized testing laboratory. The U.S. Fire Administration advises consumers to look for a UL Listed or ULC Listed label, while OSHA requires portable workplace extinguishers to be approved by a nationally recognized testing laboratory.

How to Read a Fire Extinguisher Rating

A fire extinguisher may carry a rating such as:

2-A:10-B:C

Each part communicates different information.

The Number Before “A”

The number before the letter A indicates the extinguisher’s relative effectiveness on Class A fires.

According to the U.S. Fire Administration, each unit of A is associated with the equivalent effectiveness of 1.25 gallons of water on a Class A test fire.

• 1-A corresponds to 1.25 gallons.
• 2-A corresponds to 2.5 gallons.
• 4-A corresponds to 5 gallons.

This does not mean that the extinguisher necessarily contains water. It is a performance rating.

The Number Before “B”

The number before B relates to the approximate area, measured in square feet, of a Class B test fire that a trained operator may be able to extinguish.

For example, a 10-B rating relates to a Class B test fire of up to approximately 10 square feet.

Actual fire conditions can vary dramatically. Wind, smoke, fuel depth, obstructions, and operator experience can all affect performance.

Why There Is No Number Before “C”

The letter C indicates that the extinguishing agent is suitable for use around energized electrical equipment. It does not represent a separate fire-size rating.

What Is the Best Fire Extinguisher for a Home?

For many households, a properly listed multipurpose ABC extinguisher is a practical general-purpose option. Your home may need more than one type of fire-safety product depending on its layout and hazards.

Kitchen

Potential hazards include cooking oils, towels, packaging, appliances, and energized electrical equipment.

Keep the extinguisher accessible and positioned so that you do not have to move toward the stove or through the fire to retrieve it. Do not install it where flames could immediately block access.

Garage

Garages may contain gasoline, motor oil, paints, solvents, batteries, chargers, and power tools. Match the extinguisher to the actual stored materials and equipment.

Workshop

Woodworking, welding, metal processing, chemicals, and battery-powered tools create different hazards. A general ABC extinguisher may be only one part of the required protection.

Utility or Mechanical Area

Furnaces, electrical panels, boilers, generators, and energy-storage equipment may require carefully selected extinguishers and professional assessment.

Vehicle or RV

Choose a compact extinguisher that is suitable for the relevant vehicle hazards and can be securely mounted. An unsecured extinguisher can become dangerous during a sudden stop or collision.

Where Should a Fire Extinguisher Be Placed?

An extinguisher should be:

• Visible
• Easy to reach
• Properly mounted or secured
• Protected from damage
• Located along a normal path of travel
• Positioned where the fire is unlikely to block access
• Close enough to an exit that you can keep an escape route behind you

Do not hide the extinguisher behind furniture, place it inside a locked cabinet, or store it directly beside the most likely source of fire.

Commercial placement and travel-distance requirements depend on the fire classification, occupancy, extinguisher rating, and applicable fire code. Businesses should consult a qualified fire-protection professional and the local authority having jurisdiction.

When Should You Use a Fire Extinguisher?

A portable extinguisher is intended for a fire in its early stage—not a room that is filling with smoke or a fire that is spreading across multiple objects.

Before attempting to use an extinguisher, confirm that:

1. Everyone in the area has been alerted.
2. Someone has called 911.
3. The fire is small and contained.
4. You have the correct extinguisher.
5. You can operate it safely.
6. You have a clear exit behind you.
7. Smoke, heat, or toxic gases are not preventing a safe approach.

Never allow an extinguisher to give you a false sense of security. If one extinguisher does not control the fire promptly, evacuate, close doors behind you where possible, stay outside, and wait for the fire department.

How to Use a Fire Extinguisher: Remember PASS

The PASS method is a simple way to remember the basic operating sequence:

Continue watching the area after the visible flames are gone. Some fires can reignite. Never turn your back on the fire, and keep your exit accessible throughout the attempt.

The PASS method does not replace practical training. Contact your local fire department or a qualified fire-safety provider for hands-on instruction.

What About Lithium-Ion Battery Fires?

Lithium-ion batteries power phones, laptops, tools, e-bikes, scooters, energy-storage systems, and electric vehicles. These incidents should not be treated as ordinary electrical fires.

A damaged or defective battery can enter thermal runaway, an uncontrolled heating process that may release flammable and toxic gases, produce intense heat, and cause additional cells to fail. Reignition is possible even after visible flames have been extinguished.

Warning Signs

• Unusual heat
• Swelling or bulging
• Cracking
• Hissing, popping, or crackling
• A strong or unusual odor
• Smoke or gas venting
• A sudden change in color
• Failure to charge normally

There is no universal portable-extinguisher recommendation for every lithium-ion battery size, chemistry, device, and stage of failure. Larger systems and workplaces require hazard-specific planning, training, and emergency procedures.

Businesses that store, charge, repair, or transport lithium-ion batteries should assess:

• Battery chemistry and energy capacity
• Quantities stored
• Charging arrangements
• Separation from combustible materials
• Detection and ventilation
• Fire containment
• Emergency isolation
• Employee training
• Damaged-battery quarantine
• Reignition monitoring
• Coordination with the local fire department

Explore lithium-ion battery fire-safety solutions

How Should a Fire Extinguisher Be Maintained?

An extinguisher that is damaged, obstructed, or depressurized may not work when needed.

Perform regular visual checks and confirm that:

• The extinguisher is in its designated location.
• Access is not blocked.
• The safety pin and tamper seal are intact.
• The pressure gauge is within the operating range, where applicable.
• The hose and nozzle are unobstructed.
• The cylinder is not rusted, leaking, or damaged.
• The label and operating instructions remain readable.
• The extinguisher has not been discharged.
• Required inspections and servicing are current.

Some extinguishers can be recharged after use, while others must be replaced. Inspection, maintenance, hydrostatic testing, and replacement intervals vary by extinguisher type, manufacturer, and applicable regulations.

Follow the product label and arrange professional servicing when required.