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Fire Safety and Extinguishers
Not all fires are alike. They can arise from a variety of different conditions. Accordingly, not every fire extinguisher is best suited to deal with them. Fortunately, the various types of fires are categorized as a given class and extinguishers are rated accordingly. We'll begin by discussing what is required for a fire to start, what it takes to stop them, what the various classes are, and then discuss the differences in fire extinguishing systems. We'll limit this information to that which pertains to fires likely to be encountered in an RV.
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Mark Quasius - "Cruzer"
The Fire Triangle
In order to begin, or sustain, a fire, you need to have four things present. If you remove any one of these elements fire cannot be sustained. Before you can begin to understand the various types of fire extinguishers you first need to understand fire itself. The fire triangle is a common diagram used to help illustrate the basic elements present in a fire. This triangle is now being replaced by the Fire Tetrahedron, which more accurately describes all fires by adding Chemical Reaction to the triangle, which helps in understanding chemical fires. But, for our purposes, the Fire Triangle will cover any RV fires so we'll keep it simple. The following diagram shows the Fire Triangle.
In order to have fire you need to have three key elements - fuel, oxygen, and heat. If you remove any one of these you will not be able to have fire. In order to put out a fire, a fire extinguisher must be able to eliminate at least one of these elements.
Fuel - In an RV there's an overabundance of fuel. RVs are made with a large amount of wood and composite materials and uses extensive amounts of glues and insulating foams. In addition there's plenty of wiring, which has burnable insulation, as well as propane and gasoline or diesel fuel present. The interior furniture, bedding, drapery, carpeting, all combine to assist a fire and let it spread rapidly.
Oxygen - you need oxygen to have fire. It's ever present in the air in and around the RV.
Heat - These combustible materials only need to be raised to their combustible temperature and ignition will occur. An electrical short creates intense heat in that wire, the insulation gets hot and can start on fire. Generally this wiring is run through or around highly combustible materials, such as wood paneling, carpeting, etc. A hot wire can cause any one of these fuels to easily ignite.
Fires are grouped according to standard classifications. There are a few key identification words that will help you remember these classes which I'll bring up in each description. Fire extinguishers are rated to handle various classes of fires. In other words, an extinguisher that is rated to handle a class B or C fire, won't work on a class A fire. The reasons that there are different classifications of fires is because they have different fuel sources. Following are the four main fuel classifications.
Class A Fire:
Class A fires are fires from solid combustible fuels (other than metals). Examples of this are wood, paper, cloth, and plastics. Class A fires leave ash so think of using "Ash" to remember what an "A" fire is. To extinguish a class A fire you can either separate it from it's oxygen or cool it down below it's flash point. This is the easiest fire to put out and plain water can work. Ideally you'd add an element to the water (soap works) to break the surface tension and separate the fuel from it's oxygen, allowing the water to further cool down the fuel.
Class B Fire:
Class B fires are fires from flammable liquids. Examples of this are gasoline, oil, grease, diesel fuel, and alcohol. Liquids boil so think of linking up "boil" with the "B" fire classification. These fires don't get extinguished with just plain water. The fuel floats on the surface of the water and tends to spread to other areas before it can be cooled enough to stop. There are other methods available that are better suited for handling class B fires.
Class C Fire:
Class C fires are electrical fires caused by energized circuits. If it's plugged in consider it a class C fire. Note that the wire itself doesn't burn, it's the insulation and any surrounding components. Once the circuit is de-energized you can treat it as a class A fire. The class C designation serves energized circuits, where water type extinguishers could create an electrical shock hazard. Electrical wires conduit current so think of "Current" as linking up with a class "C" fire.
Class D Fires:
Class D fires are fires from burning metal. Not too many metals burn, but certain metals, such as magnesium, potassium, and sodium can. You aren't apt to find these kind of fires in an RV so we won't get into them. If you do run across this kind of fire they are next to impossible to extinguish.
Fire Extinguisher Types
Fire extinguishers come in many flavors. Just as there are a wide variety of fire types, there is wide variety of extinguishers, each designed for a specific application. Following is a brief description of the various types of extinguishers and fire fighting agents used in them.
Air Pressurized Water (APW) Extinguishers:
APWs are large tanks that are filled about 2/3 of the way with water. They are then pressurized with plain old compressed air. When the trigger is pulled the water exits out of the hose and nozzle like a giant squirt gun. APWs are used to extinguish class A fires by taking away the "heat" portion of the triangle. If you use them on a class B fire the water will spread the burning liquid farther and create an even larger situation. They also cannot be used on electrical circuits unless the power has been killed or else they can conduct electricity and electrocute the user of the extinguisher.
Carbon Dioxide CO2) Extinguishers:
CO2 extinguishers are filled with CO2 gas that is compressed to a very high pressure. They use a hard plastic horn rather than a hose with nozzle. The CO2 exits at very high pressure. Frost, which is actually dry ice, may form on the horn as well as on surrounding materials. CO2 extinguishers are rated for use on class B and C fires. They operate by displacing oxygen from the fire, effectively suffocating the fire. A side benefit is that the CO2 is cold due to it's high exit velocity so it also helps cool the fire. CO2 is generally not effective on class A fires because they may not displace enough oxygen to effectively smother it and prevent it from re-igniting.
Dry Chemical Extinguishers:
The most popular fire extinguishers available for consumer use today are the dry chemical variety. The dry chemical, which resembles baking soda, is a fine powder that fills the extinguisher and is pressurized with nitrogen to eliminate any moisture from allowing the dry chemical to pack up. The biggest reason for their popularity as that you can use them on class A, B, and C fires, which makes them fairly universal. They function by coating the fuel with a fine layer of dust to separate the fuel from the oxygen in the air. They also do not conduct electricity so they are safe to use on electrical fires.
However, dry chemical extinguishers do have their drawbacks. The first is that these units are generally undersized. The small 5 lb extinguishers typically found in an RV don't have very much volume and should be replaced with a larger 10 lb unit. Also, dry chemical leaves a real mess. The powder safely puts out electrical fires but the chemical is corrosive to electrical circuits so you'll need to do some replacing of your electrical components if they "inhale" any of this dust. They also tend to stagnate over time. Even though they are filled with nitrogen, the chemical can settle and pack up overtime. A good recommendation is to turn the extinguisher upside down and wack the base with a mallet every 6 months to keep the powder loose enough to blow out the extinguisher when it's needed. They also need to be regularly checked for any pressure leaks and require servicing, although many of these units are inexpensive throwaways that are not serviceable. In this case it's important to throw them away and replace them rather than keep a non-functional fire extinguisher around that won't work when you really need it.
Designer Foam Extinguishers:
The ABC Designer Foam extinguishers, made popular by Kidde or Hawk are rated for ABC fires. The cylinder is filled with foam that exits at high pressure. It clings to vertical surfaces, produced no toxic gasses, and is very safe to use. It functions by cooling the fuel. In addition, the Hawk ABCDK ALLFIRE extinguisher will emulsify hydrocarbons like gasoline and oil so that they cannot re-ignite.
Halon is an inert gas. Halon extinguishers are cylinders filled with pressurized halon gas and are generally coupled with an automatic sprinkler head. These were very popular in computer rooms in the 1980s and would auto deploy to basically smother the fire by removing oxygen. They were effective in fighting class B and C fires. However, it was hazardous for any occupants of the room in that they suffocated due to lack of oxygen. Halon was pretty much made illegal and you won't find it any more.
FM-200 is similar in Halon in that it is a gas used to smother the fire. However, it does not produce toxic gasses when it gets hot and won't suffocate any occupants. It's popular in computer rooms and engine compartments of boats. A very popular supplier of FM-200 based systems is the Sea-Fire company. It's a great replacement for Halon.
Aqueous Film Forming Foam (AFFF) Systems:
AFFF is used extensively by the military and fire fighting services. AFFF is an agent that is mixed with water. When the material is sprayed through a nozzle it leaves a foam blanket that prevents re-ignition, unlike plain water. It operates by removing heat from the fuel as well as by cooling it down.
A similar system is the cold fire system from Cold Fire Super Systems. These units are available as hand held units or as automatic systems. They work by providing a stream of water (or special antifreeze) that leave a foam film, similar to the AFFF systems. This is actually the automatic system that I have installed in my RV and have detailed at This Link.
RV fires can be disastrous. Your only chance to stop a fire is when it first begins. If you don't have the time to do this you need to evacuate the RV and let it burn. If you have the proper fire extinguisher, designed for your application you may have a chance, depending on the location and severity of a fire. Hopefully the above information will give you a better understanding of what makes fires tick, what kind of extinguishers are available, and how to best deal with them. The best tool in your fire fighting arsenal is knowledge and training. Know what to do when a fire starts and be prepared to implement it immediately. I am by no means a fire fighting expert so please check out the following links to sites that will further educate you. I'm just a concerned RVer who wants to be better prepared. In addition to adding a number of designer foam hand held extinguishers, I've also installed an automatic engine fire suppression system. For further details on these modifications, as well as some great links to sites that are loaded with helpful information, please check out the following links.
This article written 8/23/07