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Inflight Fire Question

Posted: Mon Sep 14, 2020 3:30 pm
by N171DN
If there were to be an inflight fire, could the cabin be depressurized at a high altitude to essentially kill the fire?

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 3:42 pm
by Starlionblue
N171DN wrote:
If there were to be an inflight fire, could the cabin be depressurized at a high altitude to essentially kill the fire?


Short answer. Sorta.

However, it probably wouldn't kill the fire in a definitive way. If a fire is uncontrollable, you need to set down ASAP.

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 4:12 pm
by VMCA787
It would also not work out too well for the pax!

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 4:40 pm
by Sokes
Operation successful, patient dead.
Jokes aside, the OP may have had oxygen masks in mind.
"Please take your masks and chill out!"

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 4:50 pm
by GalaxyFlyer
Feeding a fire oxygen via the pax won’t work too well. While depressurizing at high levels, crewv only, think freighter, might work, it might not either. Odds are fight it and land or ditch ASAP. A uncontrolled fire over water is a nightmare

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 4:58 pm
by gloom
Starlionblue wrote:
N171DN wrote:
If there were to be an inflight fire, could the cabin be depressurized at a high altitude to essentially kill the fire?


Short answer. Sorta.

However, it probably wouldn't kill the fire in a definitive way. If a fire is uncontrollable, you need to set down ASAP.


+1. You also gotta remember all those cases where fire damaged the ducts and/or oxygen generators, and depressurization wouldn't help much. As they say, there's always a pipe. Well, sort of say ;)

Cheers,
Adam

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 5:07 pm
by Flow2706
On the A320 there is a smoke removal procedure that involves raising the cabin altitude to 10000ft while descending to this altitude. Once level at 10000ft Ram Air is used to ventilate the cabin. So it’s not a „real“ depressurisation but only a minor rise in cabin altitude.
Not too familiar with business jets, but as far as I know some of them are equipped with a „cabin dump“ button that can be used to depressurise the cabin in an emergency.

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 6:43 pm
by GalaxyFlyer
Flow2706 wrote:
On the A320 there is a smoke removal procedure that involves raising the cabin altitude to 10000ft while descending to this altitude. Once level at 10000ft Ram Air is used to ventilate the cabin. So it’s not a „real“ depressurisation but only a minor rise in cabin altitude.
Not too familiar with business jets, but as far as I know some of them are equipped with a „cabin dump“ button that can be used to depressurise the cabin in an emergency.


I never saw one with a cabin dump, but I only flew six different bizjets by four OEMs. The safety valves would close trying to stop the cabin around 14,000’, so you’d override their operation and shut off the packs, I’ve never seen a system to do that. . The C-5 and most military types have a true cabin dump, hit the switch, turn off the packs and you’re at aircraft altitude faster than you can say “ouch, my ears”. It’s a red guarded switch on the engineer’s panel.

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 8:45 pm
by Nicoeddf
GalaxyFlyer wrote:
Flow2706 wrote:
On the A320 there is a smoke removal procedure that involves raising the cabin altitude to 10000ft while descending to this altitude. Once level at 10000ft Ram Air is used to ventilate the cabin. So it’s not a „real“ depressurisation but only a minor rise in cabin altitude.
Not too familiar with business jets, but as far as I know some of them are equipped with a „cabin dump“ button that can be used to depressurise the cabin in an emergency.


I never saw one with a cabin dump, but I only flew six different bizjets by four OEMs. The safety valves would close trying to stop the cabin around 14,000’, so you’d override their operation and shut off the packs, I’ve never seen a system to do that. . The C-5 and most military types have a true cabin dump, hit the switch, turn off the packs and you’re at aircraft altitude faster than you can say “ouch, my ears”. It’s a red guarded switch on the engineer’s panel.


Well, the jet I am very familiar with has exactly that kind of button and works very digital: outflow valves open!

It is part of a last resort attempt to remove smoke, not suppress the fire per se.

Re: Inflight Fire Question

Posted: Mon Sep 14, 2020 9:55 pm
by CosmicCruiser
In the cargo world yes it was part of our chk list. There was a DC-10 that had a cargo fire. They performed the chk list which included raising the cabin and going on O2. The made an emergency ldg and the fire remained subdued until the fire dept decided to hand crank open the cargo door. The fire blossomed and the plane burned into on the runway.

Re: Inflight Fire Question

Posted: Tue Sep 15, 2020 6:45 am
by spacecadet
UPS flight 6 vented the cargo bay and crashed anyway. I'm not an expert on lithium battery fires, but my understanding is that once thermal runaway begins, the fire is not easily put out even when starved of oxygen.

Valujet 592 had an airtight cargo hold, but that's kinda moot if you give the fire its own oxygen supply...

Re: Inflight Fire Question

Posted: Tue Sep 15, 2020 7:43 am
by tommy1808
gloom wrote:
Starlionblue wrote:
N171DN wrote:
If there were to be an inflight fire, could the cabin be depressurized at a high altitude to essentially kill the fire?


Short answer. Sorta.

However, it probably wouldn't kill the fire in a definitive way. If a fire is uncontrollable, you need to set down ASAP.


+1. You also gotta remember all those cases where fire damaged the ducts and/or oxygen generators, and depressurization wouldn't help much. As they say, there's always a pipe. Well, sort of say ;)

Cheers,
Adam


plus that iffy detail of fire burning quite well in air up to 50k feet. So that works more by the rapidly expanding gas cooling the fire/burning material than depriving it of Oxygen.

best regards
Thomas

Re: Inflight Fire Question

Posted: Tue Sep 15, 2020 4:50 pm
by fr8mech
Old folks know from school that 3 things are needed for fire. Fuel, oxygen & heat...ye old fire triangle. Now-a-days, we are taught about the fire tetrahedron...fuel, oxygen, heat & the chemical reaction. To extinguish a fire, one of the components must be removed.

When we depressurization a cabin, we reduce the amount of oxygen available, thus darkening down the fire, but until the heat is removed or the fuel removed, the fire is still there, waiting for an increase in oxygen. I guess, if you stay high enough, long enough, you may cool the fuel enough to put the fire out. But, since, “get on the damn ground” is pretty high up on the checklist for an in flight fire, we will be increasing the amount of oxygen as we head down.

Depressurization will buy you time, but chances are, it will not extinguish a large or deep-seated fire.

Note: introduce chemicals or combustible metals, and I’m thinking depressurization won’t buy you much time.

Re: Inflight Fire Question

Posted: Tue Sep 15, 2020 5:59 pm
by LyleLanley
spacecadet wrote:
UPS flight 6 vented the cargo bay and crashed anyway. I'm not an expert on lithium battery fires, but my understanding is that once thermal runaway begins, the fire is not easily put out even when starved of oxygen.


Bingo. Lithium fire produces its own oxygen and hydrogen gas as a byproduct of the reaction - two sides of the fire triangle. The only thing you can do with lithium fire is decrease the temperature to control the thermal runaway. Smothering with water helps but brings its own hazards on an airplane.