Sad Story

[Barefoot]

the original Halon, does not so much displace oxygen as interfere with the combustion process.

BTW I used to have a rather large diesel motorboat that was equipped with a large Halon (the older stuff) fire extinguisher. I was working in the engine room when another person accidentally discharged the system. The agent was invisible but the sound scared the **** out of me and it costed big bucks to refill the tank but I am here to tell the story.

I'm in the same business that Steve retired from and know enough to be dangerous about halon and its replacements.

There are 2 main halons, 1301 and 1211. 1211 discharges mainly as a liquid and can be distributed throughout an enclosed area with reasonable precision. 1301 discharges as a gas, and is more difficult to precisely control. Michael is correct that the main way that halon extinguishes is by interfering with the chemical process of combustion. In something with a known volume, like an aircraft cabin, (or a boat's engine room), a system can sized to discharge enough halon to stop the fire, but not displace much of the oxygen. The standard we design and test to is 9% by volume. The standard for incendiary rounds is different, but that's a discussion for another day.

 

[Bob_Spidell]

What's the danger? I googled 'injury or fatality from halon discharge' and got mostly links to incidents with CO2 extinguishers.

My story (I've told it here before but it's worth repeating): Years ago I was struggling with typical SU fuel pump problems. In order to eliminate electrical issues I'd run a line directly from a hot terminal on the fuse box to the fuel pump. Once, I was swapping pumps and had cut power with the battery cut-off switch--mine works as expected--but had forgotten about the hot line. Of course, when I disconnected the fuel pump I spilled a bit of gas--just a couple tablespoons, probably--and somehow the hot lead touched the chassis, sparked and ignited the fumes. I had a gasoline fire in the rear axle well, with two gas-filled, dripping, open fuel lines inches from the tank (I was in my garage). I was just a few seconds from loss of Healey, loss of my house and most likely major burns if not loss of life (which I probably would have preferred). I remembered a small Halon extinguisher my flight instructor had given me to carry in my flight bag; I'd put in the glovebox as I was driving more than flying at the time. I moved fast--you can imagine how fast--grabbed the extinguisher, pulled the 'pin' and got the burgeoning conflagration/explosion out with a couple short bursts. From ignition to extinguished was probably less than 10 seconds; so quick I didn't even blister any paint. I'll take my chances with Halon.