The rollbar seems to be a...
The rollbar seems to be a handy mounting spot for the fire extinguisher, but is it? Will that small plastic strap holding the extinguisher in place during an accident stay fastened? Five pounds of projectile is not something that I would want to meet up with. A couple of hook-and-loop fastening straps with a pull tag would go a long way in keeping it in place, but still provides full and quick access.
At our local 4x4 club's outing last week, one of the members showed me a new fire extinguisher that he had just bought. He said it was foam and wouldn't make a mess like a dry chemical extinguisher would. I told him that was great but to look at the extinguisher closely. Did he see a UL rating number on it anywhere? Nope. In fact, this extinguisher had no markings at all. It didn't even have a gauge on it to let me know if it was charged.
What the extinguishing agent most likely was is a material called AFFF, which is short for aqueous film-forming foam. This was developed and used by the U.S. Navy back in the early '60s to fight liquid fuel fires in conjunction with a material called Purple K (potassium bicarbonate). The PK is used to knock down the fire, and the AFFF produces a high-quality foam blanket that floats on the fuel surface. By quickly covering the fuel surface, AFFF provides a fast knockdown of hydrocarbon fuel fires (gasoline, kerosene, diesel, etc.). These are sometimes referred to as "wet" chemical fire extinguishers, and the main factor is cutting off the fuel from the oxygen supply (the air) by putting a non-combustible layer of soapy chemical between them. It also has a cooling effect on the fuel, which helps to prevent re-ignition. They are not designed for Class C electrical fires and will to some extent work on Class A fires.
While AFFF extinguishers work great, it takes a lot of material to do the job. The small (less than a half quart) extinguisher he showed me just wasn't going to do it. Well, maybe for a small fire, a very small fire. And definitely it's not the extinguisher to be carried for a vehicle fire. Just as an example, to obtain a UL 1 A 20 B rating, an AFFF extinguisher must have at least six liters of capacity. That's about 13/4 gallons and costs over $100. Plus, it does not have a rating below 40 degrees Fahrenheit. Being a water-based material, it will freeze. Not the thing to have here in Montana when the temperature gets to below minus that number.
Okay, maybe I am getting ahead of myself and need to back up and go over the basics of fire extinguishers. My credentials, in case you're wondering, are 22 years as a professional firefighter in a Southern California department.
Let's start off with classification of fires and the extinguisher to use on them:
 Would you remember that the...  Would you remember that the fire extinguisher is hidden down here? |  Be sure to periodically check...  Be sure to periodically check the gauge on your extinguisher, making sure it's in the "green zone." |  This is not the place to keep...  This is not the place to keep your fire extinguisher. If your solvent tank was on fire, would you really want to get that close to grab the extinguisher? |
Class A fires:
Those involving paper, wood, textiles, and plastics. Water is an excellent extinguisher, as it cools the fire. The primary chemical agent used to fight these fires is monoammonium phosphate because of its ability to smother fires in these types of materials. Sodium bicarbonate works to a small extent.
Class B fires:
Those involving a flammable liquid. These can be fires where cooking liquids, oil, gasoline, kerosene, or paint have become ignited. Commonly used chemicals effective in fighting these types of fires are monoammonium phosphate, which effectively smothers the fire; sodium bicarbonate; or PK, which induces a chemical reaction that extinguishes the fire. As I mentioned at the start, wet chemicals like AFFF are also used. CO2 can be used as well.
Class C fires:
Those that involve live electrical equipment. CO2 is a common extinguisher. Both monoammonium phosphate and sodium bicarbonate are also used to fight this type of fire because of their non-conductive properties. AFFF is not used as it is electrically conductive.
There are also a couple of other classes that relate to specialized circumstances that we won't go into (such as metals), which are Class D fires.
Every UL-rated fire extinguisher will have a rating label affixed to the body of the extinguisher for the type of fire and the size of the fire that it is capable of extinguishing by the average person. An experienced person, such as a firefighter, can put out a bigger fire with a smaller extinguisher. The number and letters may read something like "2 A 20 BC." The number in front of the A, B, or C indicates the rated size of fire the unit can extinguish.
A "1 A" rating means it can put out a specially prepared stack of sticks measuring 20x20x20 inches in size.
A "1 B" rating means it can put out 3.5 gallons of the flammable liquid heptane in a 2.5-square-foot pan. A "2 B" rating would be twice that much, and so on.
In order to get a "C" rating, the extinguisher and contents must pass certain electrical conductivity measurements in accordance with UL711 and UL299, which include a non-conductivity test. Keep in mind most electrical fires involve some sort of wiring insulation.
 This 3 A 20 BC extinguisher...  This 3 A 20 BC extinguisher is mounted on the shop wall next to the main door and the vehicle door. It's a handy spot that is visible and easily accessible from either inside or outside the shop. |  This water-pressure extinguisher,...  This water-pressure extinguisher, sometimes referred to as a "loaded stream extinguisher," has a 2 A rating. While it only has an A rating, by using it properly it will do a darn good job on a liquid fire as long as you don't push the fire to another location. |  These two extinguishers use...  These two extinguishers use Halotron, a clean extinguishing agent. The advantage is that they leave no residue to clean up. The disadvantage is that they are costly at $120 for the larger red model, which only has a 2 BC rating (a comparable sized dry-chemical model would have a 1 A 10BC rating). The smaller chrome unit has only a pitiful 1 BC rating. (Photo by Jimmy Nylund.) |
This is sold as a fire extinguisher....
This is sold as a fire extinguisher. However, there is no labeling of what type it is, what rating is has, and no pressure gauge. The literature that came with it says it's a "foam extinguisher." No matter what, its small size doesn't give much confidence in its ability to put out a fire.
When it comes to an extinguishing agent, each material used has its application and both good and bad points. For instance, monoammonium phosphate, while working great and being considered an ABC agent, is a yellow powder that forms a sticky residue that is very difficult to clean up. Both PK and sodium bicarbonate can be abrasive and put powder, literally, everywhere. You generally won't find a PK extinguisher in your big-box stores, as they are quite expensive though they do have a higher rating. One major problem with a dry chemical such as sodium bicarbonate is that it has a tendency to settle and pack, especially when subjected to vibrations like those encountered with a vehicle. It's a good idea to set up some kind of a program where you remove the extinguisher from the bracket and turn it upside down and give it a few whacks against a post to loosen up the powder. Maybe do it every time you change your oil. A 2.5- to 3.3-pound extinguisher is the most common one you will find in most auto parts, marine, or general merchandise stores. High-pressure water is a very effective firefighting tool when used properly on a Class A type fire. Trained professionals such as firefighters sometimes even use it on Class B and C fires under special circumstances.
I dealt a bit on AFFF at the beginning. When used in large volumes, it is an excellent extinguisher. And even the very small handheld units may sometimes work on an engine fire where liquid fuel is burning; however, most vehicle fires also consist of plastic, rubber, and cloth. AFFF is most effective on spills-that is, flat surfaces, not irregular surfaces like engines, where it can run off and break surface tension.
CO2 is an excellent extinguishing agent for a Class B or C fire, being non-conductive and leaving no residue behind. Its limitations are its short range and the need to be in a heavy container.
I should also mention an extinguishing agent called Halotron. It's what's referred to as a "clean" extinguishing agent. Its real name is HydroChloroFluoroCarbon. It is discharged by argon gas as a rapidly evaporating liquid which leaves no residue. It effectively extinguishes Class A and B fires by cooling and smothering, and it will not conduct electricity back to the operator. It is approved for use on Class A, B, and C fires, depending on the size of the extinguisher. Halotron is intended for use in areas formerly protected by Halon 1211, such as in areas of sensitive electronic equipment. It dissipates, leaving no residue. Race cars of all types use this type of extinguisher for onboard systems within confined spaces. It is also available in portable handheld units. It's a very superior firefighting agent but also very expensive-a 5-pound extinguisher with a 10 BC rating will cost in excess of $100. Another downside is that when used outdoors, it doesn't take much wind to blow it off course. Its method of action is actually a "chain-breaking reaction" similar to a chemical reaction like spontaneous combustion in reverse.
This mounting location is...
This mounting location is accessible to both driver and passenger, and uses a quality over-center metal strap to hold the extinguisher in place. (Photo by Jimmy Nylund.)
What's the bottom line when it comes to fire extinguishers? All I can tell you is what I use. My first line of defense is actually a 5-gallon bucket of water kept next to my grinders. Not only is it good for cooling off parts, it makes for one heck of a fire extinguisher and it's pretty low-cost. Each one of my vehicles has at least a 10 BC sodium bicarbonate extinguisher. I have one in my enclosed trailer as well as in my camper. In the shop there is a 5 BC and a 2 A 20 BC extinguisher mounted on the wall. There is also a 2.5-gallon water pressure extinguisher on the wall. In my house, there is a 1 A 10 BC in the kitchen. Note that I said "mounted on the wall." Don't set your extinguisher on the floor! First, it can fall over and break off the head, and well, you have a heck of a mess to clean up. Second, you just won't remember where it is when you need it, especially when other things get pushed in front of it. Mount it on the wall in plain sight, about chest-high.
Don't "test" a dry chemical extinguisher by squirting out a bit of the material. The extinguishing agent can stick under the valve and prevent it from totally sealing, and the expelling gas will leak out, making your "tested" extinguisher useless. Any quality extinguisher will have a gauge on it, so periodically look at the gauge and make sure it still is in the green zone.
While I was working on this story, a friend sent me a video of a very expensive sand rail burning in the dunes. In the background you could see lots of other vehicles parked, and people were madly tossing sand on the fire that apparently was being fed by a fuel leak. Before they got the fire out, it did a considerable amount of damage to the vehicle. Funny thing is, no one nearby had a fire extinguisher! A $20 fire extinguisher could have saved about $10,000 worth of damage or a potential total loss.