Fire Extinguishers

The single most important thing about buying a fire extinguisher: match it to what might actually burn in the room. There are several different types of fire extinguishers, designed for extinguishing fires arising from different sources. The correct fire extinguisher must be used in each instance. Using the wrong extinguisher could result in increasing the fire and endangering yourself and other members of your household. A water unit on a grease fire isn’t just useless — it can be fatal.

Start by looking at the fuel. The first step is to look at what materials are present in the area to be protected from fire. For most homes and shops, that means an ABC multipurpose dry chemical unit. There are multipurpose fire extinguishers that might be labeled “B-C” or “A-B-C” that can be used on most types of home fires. Most home improvement stores carry multipurpose fire extinguishers that cover Class A through Class C.

One Montana note worth filing away. Water-based extinguishers freeze. Freeze-protected models exist, but for an unheated garage, shop, or cabin, a dry chemical ABC unit sidesteps the whole problem — no water to turn to ice when the temperature drops below zero.

Fire Classes and the Agents That Fight Them

Every extinguisher is built for specific fuels. Get this part wrong and nothing else matters.

Class	Burns	Examples
A	Ordinary combustibles	Paper, cloth, wood, rubber, and many plastics
B	Flammable liquids	Oils, gasoline, some paints, lacquers, grease, solvents
C	Energized electrical	Wiring, fuse boxes, energized electrical equipment, computers
D	Combustible metals	Magnesium, titanium, potassium, sodium
K	Cooking fluids	Combustible cooking fluids such as oils and fats

The agent inside determines what it can fight. Three types cover most situations. The three most common types of fire extinguishers are: air pressurized water, CO2 (carbon dioxide), and dry chemical.

Dry chemical is the workhorse. Dry chemical extinguishers put out fires by coating the fuel with a thin layer of fire retardant powder, separating the fuel from the oxygen. The powder also works to interrupt the chemical reaction, which makes these extinguishers extremely effective. They’re usually rated for class B and C fires and may be marked multiple purpose for use in A, B, and C fires. They contain an extinguishing agent and use a compressed, non-flammable gas as a propellant. The tradeoff is residue — it leaves a powder coating that’s no friend to electronics.

CO2 is the clean option for sensitive gear. These extinguishers put out fires by displacing oxygen, or taking away the oxygen element of the fire triangle. CO2 extinguishers are designed for Class B and C (flammable liquid and electrical) fires only. Good for server rooms and mechanical spaces, but two cautions: CO2 is not recommended for Class A fires because they may continue to smolder and re-ignite after the CO2 dissipates. And never use CO2 extinguishers in a confined space while people are present without proper respiratory protection.

Air-pressurized water is Class A only. Never use water to extinguish flammable liquid fires — water is extremely ineffective and may make matters worse by spreading the fire. Never use water on an electrical fire. Water is a good conductor and may lead to electrocution.

For kitchens, Class K is its own animal. Due to the higher heating rates of vegetable oils in commercial cooking appliances, NFPA 10 now includes a Class K rating, required to be installed in all applicable restaurant kitchens. Once a fire starts in a deep fryer, it cannot always be extinguished by traditional range hoods or Class B extinguishers. Class K signage typically directs users to deploy it only after a fixed hood suppression system has actuated.

Reading Ratings, Picking a Size, and Buying Certified

That alphanumeric label on the front isn’t decoration. It tells you exactly what the unit can handle. The number before the “A” represents a multiple of 1.25 gallons of water, whereas the number before the “B” represents a multiple of the area in square feet of fire to be extinguished. A classification of 1A:10B:C indicates the equivalent of 1.25 gallons of water on a Class A fire, the ability to extinguish Class B fires up to 10 square feet, and use on Class C fires.

Western Building Center carries several units across that range — a 3A:40BC, a 40A:60BC, a 10BC, and a 5BC automotive unit — covering everything from a truck cab to a full shop.

On sizing, bigger is generally better, within reason. Fire extinguishers vary in size and weight, but it is recommended to select the largest fire extinguisher that a user can safely and comfortably operate. The reason matters: small units empty fast. A one kilogram Dry Chemical Fire Extinguisher will last approximately 10 to 12 seconds. A rough rule is a 5-pound unit for living areas and a 10-pound for workshops and garages.

Never skip the certification. All portable fire extinguishers must be approved by a nationally recognized testing laboratory to verify compliance with applicable standards. Equipment that passes is labeled and given an alpha-numeric classification based on the type and size of fire it will extinguish. Always look for the “UL Listed” or “ULC Listed” label to ensure it is certified by a nationally recognized testing laboratory.

Placement, the PASS Technique, and Keeping It Ready

A perfect extinguisher does nothing if you can’t reach it. Mount it where you’ll find it under stress. Fire extinguishers should be installed on a wall near the fire exit. This way they can be easily grabbed and the person using the extinguisher can go out the same exit if the fire proves to be unconquerable. In the kitchen, put it at the door — stored so they are easy to get to but away from areas likely to catch fire. For example, locate the fire extinguisher at the entrance to the kitchen, not inside the kitchen.

When it’s time to use it, remember PASS:

• Pull the pin. Hold the extinguisher with the nozzle pointing away from you and release the locking mechanism.
• Aim low. Point the extinguisher at the base of the fire.
• Squeeze the lever slowly and evenly.
• Sweep the nozzle from side-to-side.

Know when to fight and when to walk. Most fires have to be extinguished within the first three minutes of inception for a home or office to be saved, because a fire will double in size every minute. If a fire starts, it must be knocked down almost immediately. The use of a fire extinguisher needs to be part of sound decision making that includes alerting other people in the building, performing an evacuation, activating the fire alarm, and notifying the local fire department. If it’s growing or the can runs empty, drop the extinguisher and immediately exit the building. More than anything, you should be responsible for your safety and your life.

A unit that doesn’t work is worse than no plan at all. Check it monthly. Look for easy access with nothing blocking it, the recommended pressure level on the gauge, working parts that aren’t damaged, dented or rusted, and a clean exterior free of dust, oil or grease. Maintenance varies by type — some extinguishers need to be shaken monthly; others need to be pressure tested every few years. You can recharge some while others will need to be replaced if the pressure is too low.

For dry chemical units specifically, have the extinguisher pressure tested by a professional every five years, and shake it occasionally to prevent the powder from settling.

Frequently Asked Questions

What’s the best all-around extinguisher for a house? For most homes, an ABC multipurpose dry chemical unit. Multipurpose extinguishers labeled “A-B-C” can be used on most types of home fires, and home improvement stores carry units covering Class A through Class C. It handles ordinary combustibles, flammable liquids, and electrical sources from one can.

Can I use a water extinguisher on an electrical fire? No. Water is a good conductor and may lead to electrocution if used on an electrical fire. Electrical equipment must be unplugged and/or de-energized before using a water extinguisher.

What should I use around computers and electronics? CO2 is the clean choice. It puts out fires by displacing oxygen and leaves no residue. It’s designed for Class B and C fires only. Dry chemical works on electrical fires too, but the powder it leaves behind can foul sensitive equipment.

What does a rating like 1A:10B:C actually mean? A classification of 1A:10B:C indicates the equivalent of 1.25 gallons of water applied on a Class A fire. The 10 indicates it can extinguish Class B fires up to 10 square feet in size, and the C indicates it can be used for Class C fires.

Why does an extinguisher empty so fast? Because there isn’t much in there. A one kilogram Dry Chemical Fire Extinguisher will last approximately 10 to 12 seconds. That’s why you aim at the base of the fire from the start and don’t waste a single second of discharge.

How often does a workplace extinguisher need servicing? The employer shall assure that portable fire extinguishers are subjected to an annual maintenance check. Beyond that, stored pressure dry chemical extinguishers that require a 12-year hydrostatic test must be emptied and subjected to applicable maintenance procedures every 6 years. Dry chemical extinguishers having non-refillable disposable containers are exempt from this requirement.

Who shouldn’t operate an extinguisher? Young children and older adults should not use fire extinguishers. Before fighting any fire, confirm others in the building have been alerted, someone has called the fire department, the fire is small and contained, you’re safe from toxic smoke, and you have a clear escape route. If you can’t answer yes to all of those, get out and call 911.