Do the engine fire extingushers use Co2 gas ,some kind of foam, dry powder, or do they use somthin else?

They use Halon.

Halon is used because it doesn't damage the avionics as would dry chemical. CO2 could kill the pilot if there wasn't airflow in the cockpit if the engine caught fire in flight. Foam really only works on fuel spills, that's why you don't see too many foam fire-trucks on highways.

Ok, well since bromotrifluoromethane (halon) is a toxic gas, any inhaling will be bad for humans.. Why would it matter though if it were being used on an engine?

I beg to differ RJ. In concentrations used Halon is not toxic. I have near twenty years experience in the fire suppression industry and have done many tests where I stayed in the room while Halon was discharged with nothing more than a dry throat to show after 15 to 20 minutes.

As with any non-oxygenic gas, Halon will not support life at 100% concentration, but you suffocate, the Halon itself will not kill you. CO2 will kill you, and it is sometimes used in situations where personnel are not present.

When used on aircraft engines Halon is a shoot and gone situation. The Halon releases and hopefully extinguishes the flames on its way through the engine. In most cases it does. If not, you have a reserve bottle, in most cases.

Also, I believe the Halon used for aircraft engines is the 1211, bromochlorodifluoromethane, not the 1301, bromotrifluoromethane.

Wouldn't you need something like 10% or less in the air? I have no idea what systems airliners use, just thought that it was the halon that did the suffocating, I guess it's the resulting CO2.

I don't know about airliners but the aircraft I have flown/do fly that are equipped with engine fire suppression systems use Halon 1301. I guess I don't know the difference between 1301 and 1211, but 1301 is not toxic nor is it corrosive. It's used for these reasons.

Aircraft are equipped with 1 Halon bottle per engine (the planes I am familiar with anyway). If a given engine's bottle fails to extinguish a fire you can use the other engine's bottle on that engine, too. In this sense you do have a "reserve" bottle.

You are right about the percentage. Computer rooms, etc. usually get a 5 or 6% concentration by volume and it is allowed to "soak" for 15 minutes.

Aircraft engines never really build a concentration as the Halon is discharged into the airflow at the front of the engine. I've not had much to do with civilian aircraft and learguy is probably 100% right on about those. I have dealt with C-141, C-130, and C-5 systems and there are two bottles on each of those engines. At least there was in the 70s.

Even Dupont, the inventor of Halon, doesn't know, exactly, how Halon does what it does. It is a knockoff of Freon, dichlorodifloromethane, and can be used as a refrigerant. I know that you can't even get a lighter to spark in a Halon environment. Also, at temperatures above 750 degrees Faranheit Halon turns into Phosgene, the "mustard gas" used by the Germans in WWI. In that way I guess it can be toxic, but in normal fire situations it is totally safe and doesn't create any CO2 and is not corrosive. It's a darn sight better than dry chemical for car engine fires.

Interesting, I knew they used Halon but wasn't sure about the concentrations, and also the implications of life support. Don't aircraft usually have 2 Halon fire extinguishers per engine though?

Cheers,
Chris

For 30 years I was under the impression that aircraft had 2 bottles per engine. Learguy, who knows his stuff, says the planes he's flown had one per engine with the ability to divert flow between engines. All the military transport aircraft I've worked on had 2 bottles per engine.

It depends on the airplane. The 747-400 has two bottles in the leading edge of each wing which are connected to the engines on that wing. The 737 has two bottles in the main wheel well that connect to both engines. On the MD-11 each engine has two bottles.

Allright! Finally, a man who knows.

It's different for different planes. Some new knowledge.