Fire Extinguisher Basics

Firefighters are familiar with using hoses and master stream devices for fire attack. But there are times when these aren’t the right tools for the job or they aren’t immediately available. In these cases, fire extinguishers—“handheld firefighters”—might be the way to get the job done. Incipient-stage car fires, appliance fires, incipient-stage kitchen fires, equipment fires, electrical fires, small contents fires in a home or commercial occupancy and even laboratory fires may be handled with fire extinguishers under the right conditions.

Fire extinguishers are, or should be, carried on every piece of fire apparatus. Although every fire apparatus may not carry each type of extinguisher, there should be an A-B-C extinguisher and/or a water extinguisher on every fire department vehicle, even utility vehicles. Extinguishers are also required by code in almost every sort of building. Generally, extinguishers located in buildings are appropriate for the hazards present, but in some cases, building owners purchase extinguishers as cheaply as possible to meet basic code requirements. Firefighters, therefore, can’t count on extinguishers to be stored adjacent to the threat they face. Remember: Proper fire attack requires that you use the correct extinguisher, and use it properly.

Fire Basics

To understand extinguishers, you must understand the different classes of fires:

  • Class A: Ordinary combustibles such as wood, paper, rubber, plastics, etc.
  • Class B: Flammable and combustible liquids such as gasoline or oil.
  • Class C: Energized electrical equipment.
  • Class D: Combustible metals such as magnesium, sodium, potassium and lithium.
  • Class K: Fires in cooking appliances that involve combustible cooking media (vegetable or animal oils and fats).

Note: Extinguishers rated for Class A, B, C and K fires are generally suited for any fire in the class, but Class D fire extinguishing agents are specific to the particular metal involved.

Fire Extinguisher Types

Extinguishers commonly available on fire apparatus include dry chemical (A-B-C rated or B-C rated) and pressurized water, but apparatus may also carry water extinguishers with foam or other additive, carbon dioxide extinguishers and/or dry powder (Class D agent). Some departments may have access to “clean-agent” extinguishers, or these may be located in areas such as computer rooms. Other extinguishers mounted in buildings will likely be similar to those carried on apparatus, with some commercial kitchens now equipped with Class K units. The bottom line: Evaluate the hazards in your coverage area and select the most appropriate types of extinguishers to carry on your apparatus.

There are six basic types of extinguishers.

Many truckies find a pressurized water extinguisher, or “can,” quite useful in controlling fires involving mattresses, closets or even dryers. Truckies open the door to the involved room slightly and dump the contents of the extinguisher in. They then close the door to allow the water to convert to steam and—we hope—to control the fire until the engine company can make the hoseline stretch. Tip: Mounting a strap on the unit allows you to carry it over your shoulder.

Water extinguishers have an effective range of up to 40 feet and discharge for about a minute; however, they are only effective on Class A fires and require some cleanup after use. Tip: On a water extinguisher, firefighters may find it useful to place a finger over the tip to create a “spray” pattern rather than the solid-stream that normally discharges from it.

Water extinguishers with foam or other additives have the benefit of being effective on small flammable liquids fires (Class B). Some departments routinely add foam or a wetting agent to all water extinguishers to provide this advantage, as well as a bit of improved effectiveness on Class A fires. They will require cleanup and can’t be used on electrical fires.

Dry chemical
Dry-chemical extinguishers come in many types. Most common are the multi-purpose A-B-C units that can present a corrosive problem if discharged on electrical equipment and not cleaned up quickly. Purple K, a type of dry-chemical agent, is rated only for B-C fires and has been proven to be quite effective on flammable liquid fires, as well as pressurized gas fires, when used in conjunction with AFF foam.

Some departments may carry cartridge-type dry-chemical extinguishers. The agent is in the main extinguisher canister, and a smaller pressurized cylinder is mounted to the side of the unit. A paddle on the top of the cylinder is hit to activate the pressure into the agent canister. Departments with cartridge units must ensure members are familiar with their operation.

Smaller dry-chemical extinguishers may last for only 10 seconds; larger units can last 30 seconds or more. A major disadvantage to dry-chemical extinguishers: They can require extensive cleanup after use, particularly if the agent is exposed to electronic equipment.

Carbon dioxide (CO2)
Some companies don’t carry CO2 extinguishers because they’re expensive to purchase and recharge. Although CO2 units are only rated for use on Class B and C fires, they require little cleanup and are effective in handling electrical fires without the collateral damage issues presented by dry-chemical units.

CO2 functions by reducing the oxygen in the fire area, so re-flashes can occur if the fire is in a well-ventilated area. The discharge times can be quick—mere seconds—and you must get close to the fire to be effective. Also, the CO2 discharges at low temperatures, requiring that gloves be worn to avoid contact with the extinguisher’s discharge horn. Discharging a CO2 extinguisher may also result in a small static charge that can be surprising if you’re not ready for it.

Clean agent
Clean-agent-type extinguishers are rated for Class B and C fires, and some larger ones are effective on Class A fires as well. A big plus: They require little cleanup. Halon was a widely used clean agent, until it was discovered that it had harmful effects on the Earth’s ozone. There are still halon extinguishers out there, and they can still be used, but a variety of other agents have been developed to replace halon. Clean agents don’t have the same cold issues as CO2, and discharge times vary by the size of the unit.

Dry powder
Many firefighters confuse dry-powder with dry-chemical units, but they are not the same thing. Due to the nature of Class D fires, these extinguishers don’t need to have a considerable range. In some cases, dry-powder agents can be applied by a shovel or similar implement. It’s important to completely cover the material burning for the agent to be fully effective.

Class D fires burn extremely hot, and caution is necessary since burning metal pieces can easily penetrate firefighters’ gloves and gear. Departments should preplan for emergencies at facilities with these hazards.

Class D extinguishers can be expensive, and must be selected with the proper agent based upon the flammable metals anticipated in the department’s coverage area. Many fire departments may never face a Class D hazard, but it’s worth keeping in mind that certain vehicles have magnesium engine blocks and wheels. It’s likely that other flammable metals will only become more common in vehicle construction and power trains.

Wet chemical
Wet-chemical extinguishers are specifically designed for kitchen use, or Class K fires. In many cases, they may also carry a Class A rating. At least one manufacturer claims its wet-chemical extinguisher is safe to use on energized electrical equipment, although the extinguisher carries no Class C rating.

Wet-chemical agent is discharged as a fine mist to minimize splashing of oil hazards and reduce the probability that the hazard will rekindle. There will be cleanup with Class K extinguishers, but firefighters can minimize it by applying the agent only to the fire area. Standard discharge time is about 1 minute.

Extinguisher Use

Technique is just as important as choosing the proper extinguisher, and careful application and discharge control can extend the life and effectiveness of an extinguisher. As you approach the fire, give the extinguisher a quick test to ensure it works properly. This will also give you a good idea of its range.

Approach from upwind, wearing full protective equipment. Start about 8–10 feet from the fire, and position yourself so you can retreat if the extinguisher doesn’t do the job. Work on getting a backup hoseline stretched to finish the job as necessary. If energized electrical equipment is involved, make every attempt to shut off the power to the equipment as an initial tactic. For incidents involving flammable gases and liquids, shut down the valves controlling the supply as a primary attack strategy.

Although there are exceptions, the “PASS” strategy provides a good baseline for knocking down fire with an extinguisher:

  • P—Pull the pin to activate it (some extinguishers, such as Ansul dry-chemical units, require pushing an activation lever to charge the unit);
  • A—Aim the extinguisher at the base of the fire;
  • S—Squeeze the trigger to activate the extinguisher, remembering that the bottom part of the handle is generally the carrying portion and the top part of the handle is the trigger; and
  • S—Sweep at the base of the fire, starting at the side closest to you, from side to side, pushing the fire away from you until extinguished.

Important: The PASS strategy has two exceptions: Dry-powder extinguishers, used for Class D fires, are actually “poured” onto the fire, rather than sprayed; and water extinguishers with foam or other agents are applied to create a blanket over a burning liquid.

Each type of extinguisher also has a particular range at which it’s useful. This range is by no means perfect for all fire conditions, and all extinguishers can be affected by wind or high ventilation rates. Short bursts from the extinguisher can be an effective tactic, but you must continuously monitor your progress to determine if the fire is becoming knocked down before your agent is depleted.

Generally speaking, smaller extinguishers will extinguish less fire than larger extinguishers, but it can be difficult to gauge capacity simply by size. Class C, D and K extinguishers are rated for those types of fires, not how much of that class of fire they can extinguish. The best way to understand the capabilities of various sizes of extinguishers is to practice with them on actual fires.

The Bottom Line

It’s by no means recommended that firefighters abandon the use of attack lines and master streams in exchange for fire extinguishers. However, extinguishers do have a place in firefighting and are often the most effective means of knock-down. They provide a fast attack when available, and may provide extinguishment capabilities necessary for very specific hazards.

Moreover, firefighters should be familiar with the use of extinguishers so that they can properly instruct the public. Just as public access to automated defibrillators may save a life prior to the arrival of first responders, public access to extinguishers, and the knowledge to use them correctly, allows for initial fire control. Spend a bit of time looking at the extinguishers you carry. Get familiar with them. Understand their limitations, and be sure you have the right sizes and types of extinguishers for the hazards you anticipate in your coverage area.

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