Fire Extinguisher Selection Guide

While it may be simplistic to think of a fire extinguisher as "just" a fire extinguisher, the National Fire Protection Association (NFPA) actually classifies fires, and fire extinguishers used to fight them, into five general categories. And though it can be challenging to select the right one for your needs, the following is designed to provide you important information to help make the selection easier.

The 5 Types of Fires

Here are the five general types of fires:

• Class A fires involve ordinary materials like burning paper, lumber, cardboard, plastics, etc.
• Class B fires involve flammable or combustible liquids such as gasoline, kerosene, and common organic solvents used in a laboratory.
• Class C fires involve energized electrical equipment, such as appliances, switches, panel boxes, power tools, hot plates, and stirrers. It's important to note that water can be a dangerous extinguishing medium for Class C fires because of the risk of electrical shock—unless a specialized water mist extinguisher is used.
• Class D fires involve combustible metals, such as magnesium, titanium, potassium, and sodium, as well as pyrophoric organometallic reagents such as alkyllithiums, Grignards, and diethylzinc. These materials burn at high temperatures and will react violently with water, air, or other chemicals. Extreme caution is needed when battling Class D fires!
• Class K fires are kitchen fires. This class was added to the NFPA portable extinguishers Standard 10 in 1998. Kitchen extinguishers installed before June 30, 1998, are "grandfathered" into the standard.

What do Fire Ratings Mean?

Some fires may be a combination of these five different classes. All fire extinguishers should have ABC ratings on them, which are determined under ANSI/UL Standard 711 and may look something like "4A:20B:C". Higher numbers mean more firefighting power. Here is a breakdown of the numbers and what they mean:

• The A rating is a water equivalency rating. Each A is equivalent to 1.25 gallons of water. 4A = 5 gallons of water.
• The B:C rating is equivalent to the amount of square footage that the extinguisher can cover (depending on the degree of training and experience of the operator). For example, 20 B:C = 20 sq. ft. of coverage.
• The C indicates the extinguisher is suitable for use on electrically energized equipment.

When analyzing these ratings, note that there is not a numerical rating for Class C or Class D fires. Class C fires are essentially either a Class A or Class B fire involving energized electrical equipment where the fire extinguishing media must be non-conductive. The fire extinguisher for a Class C fire should be based on the amount of Class A or Class B component. For Class D extinguisher use, the relative effectiveness is detailed on the extinguisher nameplate for the specific combustible metal fire for which it is recommended.

Types of Fire Extinguishers and Their Uses

Air-Pressurized Water Extinguishers (APW) are designed for Class A (wood, paper, cloth, rubber, and certain plastics) fires only, and water is one of the most commonly used extinguishing agents for Class A fires. APW extinguishers are recognizable by their large silver canister, and they extinguish a fire by cooling the surface of the fuel to remove the "heat" element of the fire. Weighing about 25 lbs. and 2' to 3' tall, they're filled about 2/3 with water, then pressurized with air. Sometimes detergents are added to produce foam to further help extinguish a fire.

Here are some important things to keep in mind when using APW extinguishers. Never use water to extinguish an electrical fire! Since water is an excellent conductor, it could lead to electrocution if you use it to extinguish an electrical fire. Ideally, all electrical equipment should be unplugged or completely de-energized before a water extinguisher is used on an electrical fire. Also, don't use water to extinguish a flammable liquid fire. Water is highly ineffective in extinguishing this type of fire, and it actually may make matters worse by spreading it.

CO₂ or Dry Chemical Carbon Dioxide Extinguishers, as you might expect, are filled with carbon dioxide (CO₂), a non-flammable gas under extreme pressure, and designed for Class B and C (flammable liquid and electrical) fires only. They extinguish fires by displacing oxygen or removing the oxygen element from fire. Because of its high pressure and chemical composition, the extinguishing agent comes out extremely cold and small dry ice pieces blast from the horn (as opposed to a standard hose on other extinguishers), which cools and extinguishes the fire. The extinguisher is recognizable by its hard horn (to protect the user against freezer burn) and absent pressure gauge. Ranging in weight from 5 lbs. to 100 lbs. or more, the red cylinder extinguishers are not recommended for Class A fires as they may continue to smolder and re-ignite once the CO₂ dissipates. They should never be used in confined spaces when people are nearby without proper respiratory protection.

Multi-Purpose Dry Chemical Extinguishers are usually rated for Class B and C fires and extinguish fires by coating the fuel with a thin layer of fire retardant powder which separates the fuel from the oxygen, interrupting the chemical reaction. An extremely effective extinguisher, they may also be marked for multiple-purpose use in Class A, B, and/or C fires. These red canisters range in size from 5 to 20 lbs., contain an extinguishing agent, and use compressed, non-flammable gas as a propellant.

Class K - Dry and Wet Chemical Extinguishers for Kitchen Fires are required to be installed in all applicable restaurant kitchens. Once a fire starts in a kitchen or deep fryer, it can't always be extinguished by traditional range hoods or Class B extinguishers. When used in commercial cooking operations such as restaurants, cafeterias, or other areas where food is prepared and served, a notice should be posted next to the location of the extinguisher stating "In case of appliance fire, use this extinguisher only after the fixed fire suppression system has been actuated." These fire extinguishers are intended to be used only after a built-in hood suppression system has been activated. If this type of system isn't present, then Class K extinguishers aren't required. It's important to note that extinguishing agents in many Class K extinguishers are electrically conductive. Because of this, they should be used only after electrical power to the fire-causing kitchen appliance has been shut off.

Magnetic Field Warning!

If you work around extremely strong field magnets such as magnetic resonance imaging (MRI) machines or nuclear magnetic resonance (NMR) spectrometers, only non-magnetic fire extinguishers should be used. The magnetic field of an MRI or NMR machine is so strong that it can cause a steel cylinder to fly across the room with lethal force.

As with all fire extinguishers, regardless of the type, they should be inspected on a regular schedule to ensure they are in peak working condition at all times.

To keep your fire extinguishers readily available, Zoro offers fire extinguisher brackets as well as fire extinguisher cabinets.

Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.