Most commercial flights cruise for extended periods at almost double the height of Mt Everest where the air pressure is very low. Aircraft are designed with pressurization systems that increase the internal pressure* to compensate for this so that people continue to live.
Pressurization turns the aircraft fuselage into something approximating a flying aluminum** balloon. Balloons pop, e.g. if a window falls out <link> or deflate if someone forgets to seal it <link>. In this situation, the humans on board will experience rapidly declining cognitive function before falling unconscious, possibly permanently. You have something like 10-30s of useful consciousness depending on the altitude situation.
The conventional solution to this is to fit passenger transport aircraft with an emergency oxygen system, usually stored in the panels above each seat. These systems usually use a chemical reaction to generate oxygen for long enough, approx. 10-30 mins. in this time, the pilots should have initiated an automatic*** descent to ~10,000ft or so where everyone should be OK to breath... but, oh no! the depressurization was caused by a fire started in a poorly labelled shipment of lithium batteries**** in the cargo hold! The fire suppression systems work through displacing oxygen, and lithium batteries don't care about that. The hole in the side allows the CO2 to escape and now other things ignite.
The pilots have diverted and are now on approach to a closer airfield, but acrid burning plastic fumes begin to fill the cabin, the oxygen masks do not seal and chemicals in the plastic smoke (ironically, many of them chosen because they do not burn) are horrific irritants to the lungs and eyes. Despite the fact the aircraft makes it to the ground in one piece, the smoke and panic kill many.
So, the solution to this is to replace the oxygen mask with a smoke hood<link>. These are hoods that go over the head, as hoods are wont to do, and are equipped with a similar oxygen generating system + CO2 absorber, this inflates the hood and prevents acrid smoke from being inhaled/reaching the eyes. Same advantages in a decompression scenario but with the benefit of being useful in a fire.
*but not humidity **or plastic, for the 787 fans. *** in case they pass out too **** Another one for the 787 fans.-- bs0u0155, Nov 11 2021 Windscreen blow out BA5390 https://en.wikipedi...Airways_Flight_5390 [bs0u0155, Nov 11 2021] Aircraft pressure leak Helios 552 https://en.wikipedi..._Airways_Flight_522 [bs0u0155, Nov 11 2021] Smoke hood https://en.wikipedia.org/wiki/Smoke_hood [bs0u0155, Nov 11 2021] Smoke Clearance 737 https://studylib.ne...ew-air-conditioning [bs0u0155, Nov 19 2021] I can’t tell you if it applies to all jets but if smoke becomes the #1 threat there IS a smoke clearing procedure that involves depressurizing the plane and ventilating the cabin with ram air, in which case the regular oxygen masks may be useful.-- DIYMatt, Nov 14 2021 People under stress/panic heavy breathe. A hood isn't going to fog up, is it? Desiccant possibly.-- wjt, Nov 19 2021 //if smoke becomes the #1 threat there IS a smoke clearing procedure that involves depressurizing the plane and ventilating the cabin with ram air,//
I can't find an awful lot on this in a brief google, I suspect it's very aircraft type specific. Does, say, a 737 have a ram- air intake? I mean I know they do, but as far as I can tell, these are intakes for bleed air cooling and aren't linked to the cabin. A read through this <link> (pg9) suggests there is high flow for smoke clearance, but it's all from the packs/bleed air/apu.
And none of this helps you much on the ground.
//A hood isn't going to fog up, is it?//
There's a few things working in our favor. 1, if the mask type is an O2 generating model, then the O2 generation puts out completely dry O2. The CO2 absorbtion system, be it NaOH/CaOH or LiOH are all incredibly hygroscopic and absorb water vapor readily.
The activated carbon types, typically have mouth pieces so that the breath doesn't get into the same space as the eye covering.
I think we're OK on this.-- bs0u0155, Nov 19 2021 Is there a psychological barrier?. Hey, really scared person put this bag over your head. You will feel better,trust me.-- wjt, Nov 20 2021 So perhaps an oxy mask/goggles combo - of course, as a scuba diver / motorcycle helmet wearer, my opinion is valueless ...-- normzone, Nov 25 2021 random, halfbakery