We haven't actually used an H3R Halon extinguisher yet, and hopefully we won't have to, but having used Halon in the past, we know how well it works. Those of you who have used a dry chemical extinguisher on your vehicle (or any belongings, for that matter) can probably relate to why we tend to carry two extinguishers. We'd gladly hand our dry-powder one to anybody who wants or needs to use it, but wouldn't use powder on our own stuff unless absolutely necessary. So why not just let anybody use our Halon, or carry two Halon extinguishers? First and foremost, availability.
For the past 10 years, Halon has been virtually Unobtainium. Apparently, some great minds decided that it may be better to let things burn, no matter what the toxicity of the smoke, than to let some Halon into the atmosphere. However, there are things that are best left unburnt, even in the eyes of the save-us-from-ourselves groups, such as computer systems and aircraft. Sure, dry chemicals would likely put out fires in airplanes, too, but may well destroy the electrical system of the craft in the process, and possibly blind the pilots, effectively creating a delayed but really large fire at the moment of impact. If somebody discharged dry chemicals into a computer system, well, the corrosiveness would pretty much destroy it. We wouldn't wish that on even the IRS.
We were very glad to recently find out about H3R, a company selling 1.3- through 5-pound Halon extinguishers for automotive use. Since Halon production has been outlawed, H3R uses recycled 1211 from a finite supply. Consequently, if dry chemical extinguishers were price-competitive before, they sure are now-but you get what you pay for. H3R wants $82 for a 1.3-pound unit and $135 for a 2.5 pounder (chrome versions are obviously more), but perhaps the best value we found on H3R's Web site was the refurbished 2.5-pound extinguisher for just $90.
Either way, you should put things in perspective. Surely you already have an extinguisher, but is it an old dry chemical unit carried purely to satisfy the requirements of organized runs? If so, the powder may well be clumped at the bottom by now and it won't work at all-which, all things considered, could actually be a good thing. If the value of your four-by exceeds the cost of an adequately sized Halon extinguisher, wouldn't it make sense to have at least one on board? And your tow rig and trailer are certainly also worth more than what another really good extinguisher costs. Look at Halon as extremely cheap insurance for the vehicles and items you care about, which likely includes the garage. Maybe even the house.
Halon can put out a tire fire, which is a really bad scenario for a vehicle. Halon can be squirted into an engine compartment after just cracking the hood open enough to get the nozzle inside (instead of opening the hood and providing oxygen for the fire to flare up) or even through the radiator or a fenderwell. Got a dash on fire while going down the highway? Grab the Halon and put it out, then open a window and come to a stop when it's safe to do so. We wouldn't even want to think about the consequences of discharging a powder extinguisher inside a pickup cab while driving-about the best that could happen would be that somebody got it on video and you'd end up in a Vonage commercial.
We once had to use a dry chemical extinguisher to put out a fire, caused by ATF hitting a hot header. It was a really nice vehicle, but after seeing the result of the corrosive effects of the powder, we wondered if it wouldn't have been better to let it burn. Not because of insurance reasons, mind you, because insurance isn't meant to cover our bad luck; it's a defense against other people's dumb acts. No, it was just so depressing to see engine parts that looked as if they'd recently been found on the Titanic. Halon doesn't do that to your four-by-it leaves no trace whatsoever. You can blow your birthday cake candles out with it, if you feel like it. Unlike a powder extinguisher, it's also still useful even after squirting some of the contents out of it. Also, H3R can service and refill Halon extinguishers, should you end up having to use yours, or if you have an old one lying around that needs freshening up.
While not always A-rated, Halon is still effective on wood, upholstery, and such (water works very well, too), but it's on B- and C-rated fires that Halon really shines. "B" is oil, gasoline, and the like, where Halon stops the chemical reaction of the fire and puts it out. The same goes for "C" (electrical) fires, which aren't exactly uncommon on four-wheel-drive vehicles.
Given the choice, which at least for the near future we are, Halon extinguishers are definitely the way to go. The only thing better would be not to need an extinguisher at all, but as long as there is oxygen, fuel, and heat, we're going to have fires.