The Right Type of Fire Extinguisher for Any Emergency
Fires can vary by ignition source, fuel, and oxygen content. As a result, different fires require different approaches to extinguish.
Knowing the classes of fire and fire extinguishers used to extinguish each one ensures your crews meet code requirements, minimize risk, and keep projects on schedule.
Classes of fire
Fires are organized into five classes based on their fuel or ignition sources: Class A, B, C, D, and K.
Class A fires
Class A fires are the most common. Their fuel sources include wood, paper, trash, cloth, rubber, and some plastics.
Class B fires
Class B fires burn flammable gases and flammable and combustible liquids, such as gasoline, paint, finishing waxes and plastics, oils, propane, butane, and hydrogen.
Cooking oils and fats are excluded from this category because of their higher flash point.
Class C fires
Class C fires are categorized by ignition source, rather than fuel source. Fires involving energized electrical equipment, like fallen power lines or frayed electrical wiring, are considered Class C.
Once the electrical source is powered down, the fire would fall into one of the other classifications based on its primary fuel source.
Class D fires
Class D fires involve combustible metals. Industrial sites, manufacturing sites, and construction sites that involve cutting or grinding metals can be at risk for Class D combustible metal fires. Common combustible metals include magnesium, titanium powder, and aluminum powder.
Lithium is a combustible metal. However, lithium battery fires are considered Class B fires since these batteries do not contain enough pure lithium to warrant Class D consideration.
Class K fires
Class K fires involve cooking oils and fats and are most encountered in residential and commercial kitchens.
Fire extinguisher types
Like any tool, fire extinguishers are tailored to their target. This is done chiefly through the extinguishing agent contained inside.
The most common extinguishing agents used to classify fire extinguishers are water, wet chemical, dry chemical, carbon dioxide, and dry powder.
Class A fire extinguishers
Fire extinguishers limited to Class A use pressurized water as the primary extinguishing agent. This makes them the least expensive kind of extinguisher. Water cools the burning material below its ignition temperature, which helps prevent reignition.
Since water can cause flammable liquid fires to spread, conduct electricity, and react with combustible metals, water fire extinguishers can only be used on Class A fires.
Class ABC fire extinguishers
Some extinguishers account for multiple fire classes. ABC fire extinguishers, like the 2.5-lb. Kidde or 5-lb. Amerex, use a dry chemical agent to smother fires, cutting off the access to oxygen required to continue burning.
Because they cover the most common ignition and fuel sources, these multipurpose fire extinguishers are the most versatile. This versatility makes them the recommended choice for multifamily properties and other high-occupancy or high-traffic areas.
Class BC fire extinguishers
Class BC fire extinguishers are suitable for putting out burning flammable and combustible liquids and flammable gases, as well as electrical fires that are not burning Class A materials.
BC fire extinguishers commonly use carbon dioxide (CO2) as an extinguishing agent.
Class BC extinguishers do not contain the cooling agents present in Class A or Class ABC extinguishers. This leaves the Class A fuel sources open to reignition, so BC extinguishers should not be used on wood, paper, or cardboard fires.
Class C fire extinguishers
There are not exclusively Class C fire extinguishers since the extinguishing agent must be matched to the fuel source, not the ignition source. However, caution should be taken to use only an ABC or BC fire extinguisher on fires involving live electricity.
Class D fire extinguishers
The unique properties of combustible metals require a unique approach to extinguishing. Class D fire extinguishers use a dry powder, which can contain graphite, sodium chloride, or copper powder. These cut off the burning metal’s access to oxygen, which prevents it from continuing to burn.
Class D dry powder fire extinguishers are not interchangeable with dry chemical fire extinguishers.
Class K fire extinguishers
Class K fire extinguishers are most commonly found in commercial kitchens and similar areas, where large amounts of cooking oils and grease exist in proximity to open flames or high heat. These are often referred to as wet chemical fire extinguishers.
Fire extinguisher classes
| Class | Extinguishing Agent | Target Fuel/Ignition Source(s) | Applications |
|---|---|---|---|
| Class A | Water | Wood, paper, cloth, cardboard, trash, light plastics | Multipurpose, commercial and residential buildings |
| Class ABC | Dry chemical | Class A fuels, flammable or combustible liquids, flammable gases, electrical fires | Multipurpose, commercial and residential buildings, storage facilities, construction sites |
| Class BC | Carbon dioxide | Flammable or combustible liquids, flammable gases, electrical fires | Multipurpose, commercial facilities |
| Class D | Dry powder | Combustible metals | Industrial and manufacturing facilities, industrial warehouses |
| Class K | Wet chemical | Cooking oils and grease | Commercial and residential kitchens |
Fire extinguisher size ratings
When purchasing fire extinguishers, you may see a series of numbers, letters, and colons (e.g., 1-A,10-B:C or 4-A:80-B:C). This is the extinguisher’s UL rating.
The first half indicates water equivalency. For example, a 1-A in the UL rating means that the extinguisher has the same extinguishing ability as 1.25 gallons of water.
The second half indicates the extinguisher’s coverage distance. For example, 10-B:C means that the extinguisher contains enough extinguishing agent to cover 10 square feet when used properly.
This information can help you determine how many fire extinguishers you need to meet fire safety standards for your building.
Class D and Class K fire extinguishers do not include size ratings but rather list the volume of extinguishing agent in pounds or gallons.
Understanding fire extinguisher requirements
The National Fire Protection Association uses “maximum travel distance” to regulate the placement of portable fire extinguishers.
“Maximum travel distance” refers to the furthest distance an occupant would have to walk, including around walls or through hallways, to reach a fire extinguisher.
| Fire Extinguisher Class | Maximum Travel Distance |
|---|---|
| Class A | 75 feet |
| Class B | 30 feet |
| Class D | 75 feet |
| Class K | 30 feet |
Construction site fire extinguisher requirements
The Occupational Safety and Health Administration requires one fire extinguisher, rated 2A or above, for every 3,000 square feet of protected building area. The maximum travel distance cannot exceed 100 feet.
Additionally, whenever five gallons of flammable/combustible liquids or five pounds of flammable gas are in use on the jobsite, a 10B fire extinguisher must be present within 50 feet.
Ferguson can help you stay fire-safe
As a leading supplier of fire safety products, we offer a variety of fire extinguisher classes. Shop fire extinguishers to meet your facility or jobsite requirements. Our team can help you identify the right products for OSHA and NFPA compliance.