Fire Extinguishers

Defining fire.

Firefighters are taught that fire is the rapid oxidation of a fuel with the evolution of heat and light (?) As soon as they learn what it is, they are taught how to put it out. It's a shame that more emphasis is not put on preventing the fire from happening ! (Dave's pet peeve). Anyway, 4 things need to happen just right to make fire; a fuel must combine with a heat source in enough air to begin off-gassing; then, a chemical chain reaction begins, and the gas is ignited by the heat.

+ +O^2 =

Translation: most things that burn need oxygen and a heat source before fire occurs. Further translation: keep the fuels away from the heat sources, wherever possible, and you too can prevent fires from occurring.

Types of fire.

There are 4 types of fire commonly seen, and 1 type rarely seen--but possible, in your daily life. These types are indicative of the fuel types or fire causes.

Class "A" fires involve ordinary combustible material as fuel (most common), such as: wood, paper, plastic, rubber, and cloth. The international pictogram is a green triangle with an A inside.

Class "B" fires involve flammable liquids and gases, exclusively. The international pictogram is a red square with a B inside.

Class "C" fires involve energized electrical equipment. When the electricity is cut off, these fires are then treated as a Class A or B type. The international pictogram is a blue circle with a C inside.

Class "D" fires involve combustible metals. These aren't seen very often, but sometimes these metals are used in automobile and machine manufacturing and construction. The international pictogram is a yellow star with a D inside.

Class "K" fires involve a liquid cooking medium (oil or grease).

Types of fire extinguishers.

The most common portable fire extinguisher is the "dry chemical" "stored-pressure" type. This type contains a very dry, specially formulated chemical or powder that is meant to interrupt the chemical chain reaction necessary for flame development--so the fire goes out ! Dry chemical fire extinguishers are made for each type of fire. You must anticipate the potential hazard(s) and be sure to match the type of fire extinguisher with the type of fire that might occur. A 5 to 6 pound dry chemical extinguisher is rated at 2 or 3A:40B:C.

There are also specially formulated "wet chemical", stored-pressure fire extinguishers that work in about the same way. They also provide a limited "cooling" and "smothering" effect. Most wet chemical fire extinguishers are rated from 40B:C and higher. A very effective hybrid portable is the foam type. This extinguisher is good for Class A, B, & C fires. A 2-liter foam extinguisher is rated at 8A; 70B; C. The 6-liter Class K extinguisher, for cooking mediums, is a wet chemical type.

There are also stored-pressure water fire extinguishers. Each one carries 2.5 gallons of water, and some have special additives to keep them from freezing or to make them more effective. Without additives, the water extinguisher is 2A-rated.

Stored-pressure fire extinguishers are immediately ready to use--they have the expellant means already inside the shell (canister). This is usually a charge of (inert) Nitrogen gas.

Non-stored-pressure fire extinguishers do not have their agent under pressure, but carry the pressurizing cylinder on the side. This type must be pressurized before it can be used.

Fire extinguisher rating system.

The rating system for portable fire extinguishers can be very confusing. It is based on the types of fire, i.e., A:B:C:D:or K. When testing began long ago, labs used a 3'x3'x3' "crib" of loosely stacked wood. If a fire extinguisher and a trained operator could extinguish this crib of wood when fully involved with fire, it received a 1A rating. To visualize higher ratings, just multiply the volume of the "cribbed" wood stack. A 5 to 6 pound dry chemical extinguisher is rated at 2 or 3A depending on its chemical mixture. All other things being equal, a 4A rated extinguisher should be able to extinguish twice as much fire as a 2A rated extinguisher. Remember: this is in a lab with a trained operator !

The standard rating for flammable and combustible liquids is 1 square foot of surface area of a "pooled" liquid at an appreciable depth (1/4" or more). Liquids will always seek a lower place, so they will always attempt to "pool" and therefore contain themselves. Liquids that are unconfined pose a greater risk, and are referred to as "three-dimensional" spills. The rating for one unit (1'x1') is 1B. The smallest B:C type extinguishers (2 to 3 lb.) have a 5 to 10B rating. All other things being equal, an extinguisher rated 40B should be twice as effective as one rated 20B.

There is no standard rating for Class C and Class D fires. When a Class C fire is de-energized, it is treated as a Class A or B type.

Class D fires burn ferociously, they may burn in the absence of air, and they are highly reactive to water. These fires must be completely covered with a compatible agent to at least 1/4" to 1/2", or more.

Class K fire extinguishers (6-liter) are rated 2A:1B:C:K. Although this doesn't seem like a lot, these extinguishers are specially formulated to be compatible with most commercial restaurant hood fire suppression systems, and they can certainly be used at home. They offer easier clean-up and less down-time after use.

When to use portable fire extinguishers.

A common misconception is that the primary purpose of portable fire extinguishers is to put out small fires before they get bigger. While that is surely a secondary purpose, you should select them, place them, and maintain them as if your life depended on them ! The primary purpose of a fire extinguisher should be for life safety--for your protection during an emergency escape.

To stop a small fire from getting bigger, a portable fire extinguisher should still only be used under certain circumstances:

~ The fire is small and not developing quickly.

~ The user knows how and is comfortable with using the extinguisher.

~ The material involved in the fire is known and not hazardous.

~ The extinguisher is compatible with the fuel that is involved.

~ The area of the fire is not already filled with heat and smoke.

~ The user needs no personal protective equipment.

~ The way out is not blocked in any way.

The fire department should always be called first, if possible !

If all of these conditions are not present, it probably will not be safe for you to fight the fire alone. CALL THE PROFESSIONALS !

How to use portable fire extinguishers.

Remember to PASS !

Pull - the safety pin;

Aim - the nozzle or hose at the base of the fire;

Squeeze - the lever to release the agent;

Sweep - the agent from side-to-side at the base of the fire.

Matching the extinguisher with the hazard.

Using a portable fire extinguisher that is compatible with the type of fire you have can be very important to your safety and to the results of the application. The rating system indicates which type (single-purpose) or types (multi-purpose) of fire a particular extinguisher can effectively be used.

Reading the label.

Reading the manufacturer's label on a portable fire extinguisher is vitally important. Everything you need to know can be found there. Look for the type of fire it is compatible with, the relative effectiveness rating, the type of agent that is inside, operating and maintenance instructions, and approvals of credible testing laboratories, such as Underwriter's Laboratories (UL).

Proper mounting is important.

The proper placement of your portable fire extinguisher is very important. You want it near the fire hazard, but not too close. You want it to be nearby, but also on the way out of the room, area, or house where it is strategically located. Don't cover them up or allow them to be used as a coat rack ! Extinguishers should always be within sight and ready to use at all times--when you need them, there will be no time to waste trying to gain access to this life saving device.

Proper maintenance is essential.

Proper maintenance of your portable fire extinguisher is essential to your piece of mind, and it ensures that the extinguisher will function properly when you need it most. Each manufacturer puts recharge and maintenance information on the label, which is affixed to the extinguisher. Generally, all aluminum and steel shell, stored-pressure extinguishers must be inspected at least annually, maintained every six years beginning with the date of manufacture, and hydro-statically tested and maintained every 12 years beginning with the date of manufacture.

In residential use, the owners can perform inspections. A specialty contractor must be used to perform the maintenance and hydro-test. In commercial use, all inspections, testing, and maintenance must be performed by a "qualified" contractor (and they are not created equally !). Inspections can and should be performed monthly, and in places of employment this is required by OSHA.

Inspections are non-invasive, and consist of looking at extinguishers to see that they are where they should be, that they have not been damaged or used, and that they appear to have adequate pressure by some indicator (most commonly a gauge).

Maintenance includes a discharge of the agent, disassembly, cleaning, reassembly, and pressurization. This constitutes a full functional test.

A hydrostatic test assures the integrity of the shell or canister of the extinguisher. The shell is emptied and filled with water, and then pumped to double the working pressure of the extinguisher--usually 200~400 psi. If the shell does not burst (rarely ever happens), it is dried and "maintenance" is performed.

Making your selection.

Now that you know a little more about portable fire extinguishers, it's time to make your selection. How many do you need, of what type and size should they be, and where is the best place to put them in your dwelling or business ?

Generally speaking, you need one or more for life safety and protection of property and one for each special hazard you may have. They should also be in every "compartment" of your dwelling--this is defined by locked doors or floor levels.

To simplify the process, you should have one minimum 2-A rated extinguisher that is easily accessible on each occupied floor level of your dwelling. To minimize size and weight, this is best accomplished by installing a 5-lb (or larger), A:B:C rated, multi-purpose, dry chemical type of extinguisher or 2-liter foam type. The 2.5 gallon water extinguisher meets this minimum, but is larger and heavier. The 6-liter Class K wet chemical extinguisher also carries a 2-A rating. The advantage of water, foam, and wet chemical extinguishers is less mess and easier clean-up after using them.

In addition to this, you should have a minimum 10-B:C rated (or larger) dry chemical extinguisher in the kitchen (but not too close to the stove), however the best choice may be the 2-liter foam type. A Class K wet chemical extinguisher would be larger and heavier, but also much more effective. The foam and wet chemical types would definitely be easier to clean-up after use. An A:B:C-rated multi-purpose dry chemical extinguisher in the 2.5 to 5 pound size would also be small and effective.

You should also place minimum 2A:40B:C rated (or larger) extinguishers in the garage, workshop, barn, or other out-buildings. This can be accomplished with a 5-lb or larger multi-purpose dry chemical type extinguisher or the 2-liter foam type. The farther away help is, the more protection you may need.

Also, as a general rule, having more of the right sized extinguishers can be more beneficial and less expensive than having fewer and larger extinguishers.

Portable Fire Extinguishers