Originally Posted by
ATC Watcher
Not a medic but I think the critical part is from 400 to 300 , at 4000 ft/min (typical emergency descent on most types) say 2- 3 min deprivation ; like a long underwater scuba dive ., brain damage ?
But from 30.000ft you get back a bit of oxygen , there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
But again I am not a brain specialist..
I just remember a decompression on a Spantax DC8 over the Netherlands from FL33 or 370 where half the O2 masks did bot deploy because stuck by nicotine tar .. Diverted to AMS. .. Nobody was injured, shocked yes, but most of the pax continued a few hours later to the Canaries...
Humans are variable creatures, of course, but three minutes is the generally-accepted period after which hypoxic/anoxic brain damage is of serious concern. The FAA tables show TUC at FL300, with rapid decompression, as 30-60 seconds:
https://www.faa.gov/pilots/training/...%2061-107A.pdf
Of course, that doesn't mean brain damage at that limit, but it does mean that few will be able to don those masks if they don't do so very quickly.
I don't mean to suggest that serious or permanent injury is guaranteed, just that it's far too serious a risk to discount. You really, really want all the pax O2 systems to work when the cabin undergoes rapid decompression.