Types of Fire Extinguishers

Types of fire extinguishers and signs: classes, agents, and OSHA requirements

Every type of fire, whether started by ordinary combustibles, flammable liquids, or electrical sources, has a specific counteracting agent that allows it to be extinguished. Because of this, there are several distinct classes of portable fire extinguishers, each with an extinguishing agent tailored to a specific fire type. Knowing the types of fire extinguishers and signs required for your facility is essential for both OSHA compliance and effective emergency response.

The National Fire Protection Association (NFPA) sets the standard for the selection, use, and maintenance of portable fire extinguishers through NFPA 10.

Fire Extinguisher

Classes of portable fire extinguishers

In the United States, portable fire extinguishers are classified A, B, C, D, and K by the type of fire they are designed to combat. Multi-purpose extinguishers are also common, including A-B-C (multipurpose) and B-C (standard) units rated for two or more fire types.

In addition to their class letter, extinguishers carry a numerical rating for the size of fire they can handle. Numerical ratings apply only to Class A and Class B extinguishers. On a label reading “2-A:10-B:C,” the number before A (multiplied by 1.25) equals the water gallon equivalent, so a 2-A extinguisher is equivalent to 2.5 gallons of water. The number before B indicates the square footage of a flammable liquid fire the extinguisher can suppress. Class C carries no numerical rating because it only confirms the extinguishing agent does not conduct electricity.

Class A fire extinguishers

Class A extinguishers are designed for ordinary combustibles such as wood, paper, cloth, rubber, and most plastics. They are the most common type found in offices, schools, and retail environments. Water and multi-purpose dry chemical are the most frequently used agents for Class A fires.

Class B fire extinguishers

Class B extinguishers cover fires involving flammable and combustible liquids, including gasoline, oil, oil-based paints, and petrol. Foam, dry chemical, and carbon dioxide are all effective agents for Class B fires. The numerical rating on a Class B extinguisher indicates the square footage of a flammable liquid fire it can suppress.

Class C fire extinguishers

Class C extinguishers are rated for fires involving energised electrical equipment. The critical distinction is that the extinguishing agent must be non-conductive. Dry chemical and carbon dioxide are the standard agents. Once the electrical source is de-energised, the underlying fire may be reclassified as Class A or B.

Class D fire extinguishers

Class D extinguishers handle fires involving combustible metals such as magnesium, titanium, potassium, and sodium. These fires require specially formulated dry powder agents and are typically found in manufacturing, laboratory, and industrial settings. Standard water, foam, or dry chemical extinguishers must never be used on Class D fires, as they can intensify the reaction.

Class K fire extinguishers

Class K extinguishers are designed for commercial cooking environments and target fires involving cooking oils, vegetable fats, and animal fats at high temperatures. Wet chemical agents are the standard for Class K. These extinguishers are required by NFPA 10 in commercial kitchens and are distinct from Class B extinguishers, which are not effective on high-temperature cooking oil fires.

Types of fire extinguisher agents

Previously, extinguishers were marked with colored geometric symbols, and it is still common to see some extinguishers featuring both old and new symbols. The extinguishing agent determines which fire classes a unit can address.

1. Water extinguishers

Water is the most common and widely used agent. Water-based extinguishers are ideal for schools, small offices, and stockrooms. Because water conducts electricity, these extinguishers must never be used on Class B or Class C fires. They may also freeze in cold climates. Overall, they are an inexpensive and non-toxic option.

2. Dry chemical extinguishers

The standard dry chemical extinguisher is suited for Class B and Class C fires. These units work by interrupting the chemical chain reaction of a fire and are non-toxic. Sodium bicarbonate-based dry chemical is more effective than water on flammable liquid and electrical fires. Multi-purpose dry chemical (monoammonium phosphate) extinguishers are rated for Class A, B, and C fires and are among the most widely deployed type in commercial and industrial facilities.

3. Foam extinguishers

Foam creates a separating layer between the flame and the fuel source, making it effective on flammable liquids. Types of foam agents include Aqueous Film-Forming Foam (AFFF), Alcohol-Resistant Concentrates (ARC), Fluoroprotein Foam Concentrates, Protein Foam Concentrates, and High Expansion Foam Concentrates. Foam extinguishers are commonly rated for both Class A and Class B fires.

4. Carbon dioxide (CO2) extinguishers

Carbon dioxide extinguishers work by reducing the oxygen level at the fire site to below 15 percent. They leave no residue because CO2 dissipates rapidly, which eliminates cleanup and makes them suitable for food storage areas, processing plants, laboratories, and industrial facilities. CO2 is toxic in enclosed spaces at high concentrations and should only be used with adequate ventilation or where users can safely exit after discharge.

Fire extinguisher signs: what OSHA requires and why they matter

Having the right extinguisher is only half the equation. According to OSHA 29 CFR 1910.157(c)(1), employers must mount, locate, and identify fire extinguishers so they are readily accessible without subjecting employees to possible injury. The word “identify” is the operative requirement. Proper fire extinguisher signs are not optional. In an emergency, workers cannot afford to search. A well-placed sign can mean the difference between a contained incident and a catastrophic loss.

For a deeper look at compliance requirements, see are your fire extinguisher signs OSHA compliant?

Types of fire extinguisher signs

1. Fire extinguisher location signs

Fire extinguisher location signs mark the exact position of a mounted unit. They are posted directly above or beside the extinguisher and are the baseline sign required wherever an extinguisher is installed. Under NFPA 10, extinguishers must be conspicuously located and visible from the normal path of travel. If the unit is obstructed by shelving, machinery, or a cabinet, a location sign above it is mandatory.

Fire Extinguisher Inside

2. Fire extinguisher arrow signs

Arrow signs direct workers to an extinguisher that is around a corner, behind equipment, or otherwise out of direct sightlines. They are posted in hallways, aisles, and approach routes leading toward the unit. Arrow signs can point down, left, or right and are frequently photoluminescent to remain visible in smoke-filled corridors. See our glow-in-the-dark sign specs to understand what compliance-grade luminescence actually requires.

3. Fire extinguisher class signs

Class identification signs are mounted with or near the extinguisher to indicate which class of fire it covers: A, B, C, D, or K. In facilities that carry multiple extinguisher types, class signs prevent workers from grabbing the wrong unit under pressure. A Class K extinguisher in a commercial kitchen, for example, must be clearly identified as such because using a standard dry chemical unit on a high-temperature cooking oil fire can cause dangerous splatter.

4. PASS method instruction signs

Fire extinguisher instruction signs guide workers through the Pull, Aim, Squeeze, Sweep technique at the point of use. These are posted directly adjacent to the extinguisher and are particularly important in facilities with high staff turnover or infrequent fire safety training. Instruction labels are typically adhesive-backed for direct application to the extinguisher body or the mounting bracket.

5. Overhead hanging signs

NFPA 10 overhead signs are suspended from the ceiling directly above the extinguisher unit. They are the most reliable option in large warehouses, manufacturing floors, or facilities with tall racking where wall-mounted signs are blocked from most viewing angles. Ceiling-hung signs maintain line-of-sight visibility from multiple directions simultaneously.

6. Floor signs and stencils

Fire extinguisher floor signs mark the location at ground level, providing visibility when wall signs are obscured by smoke, shelving, or equipment. Anti-skid vinyl floor signs and painted floor stencils are both options. Stencils offer a permanent, high-traffic solution for facilities where adhesive labels may wear quickly under heavy equipment or repeated cleaning.

Sign placement guidelines

• OSHA requires extinguishers to be visible and accessible. A sign mounted too low, behind a rack, or in a poor sighting line fails that requirement. Follow these rules to stay compliant with both OSHA 1910.157 and NFPA 10.
• Mount location signs at the right height: Signs should be visible above head-level obstructions. Mounting 60 to 80 inches from floor to bottom of sign is widely accepted best practice and keeps signs visible above desks, partitions, and shelving.
• Use overhead signs in warehouses: In facilities with tall racking or wide floor plans, ceiling-hung signs are the most reliable way to maintain line-of-sight visibility from multiple directions.
• Post class identification clearly: Workers need to know at a glance whether the nearest extinguisher is rated for their specific hazard. Class identification must be legible from the approach distance.
• Use projecting (3D) signs in hallways: A flat wall sign is only visible from directly in front of it. In hallways and corridors, projecting signs extend from the wall in a V or L shape, making them readable from both directions of travel.
• Add directional signs at decision points: Any point where a worker must choose a direction — an aisle junction, a doorway, or a blind corner — is a location where an arrow sign should be posted.

Category: Fire Extinguisher