Originally Posted by CCA
Above what altitude is forced oxygen required (Ive found from 28,000'-47,000') and if the pax O2 bottles are considered as diluter masks what altitude are they good for?
Cheers CCA
Taken directly from RAF "Human factors" Book:
"
Oxygen requirements and Cabin Pressurization"
The addition of an increasing proportion of oxygen into a pilot's breathing gas (airmix) can be used to avoid hypoxia until the point is reached at which he is breathing 100% oxygen to maintain an alveolar partial presure equivalent to that breathing at sea level. The point (100% oxy) is reached at an altiture of 33700'. However, as is noted above, it is permissable to allow alveolar partial pressure of oxygen to fall to 55 mm HG. With 100% oxygen as the breathing gas, this permits an altitude of 40,000' to be achieved. To go any higher than this it is required to deliver oxygen under pressure, ie Positive PREssure Breathing.
as a summary
0-10000 air only required, some higher function inpairment (night vision above 8k I believe, but may be wrong)
10000 - 33700 increasing percentage of oxy breathing in gas.
33700 - 40000 100% oxygen
above 40k 100% oxygen under pressure. "
HOWEVER, if you were transatlantic, would oxygen be the limiting factor? I often cruise around 26K on my fleet, and the OAT at this level is around -25C..... if you had to carry out any significant diversion, say 1.5 hours, would this not neccesarily become a limiting factor? Apparently, the body reqires significantly more oxy as well when cold (to generate heat) than warm, thereby compounding the problem. I was led to believe, and I am not sure how truthful this is, that due to differing oxy reqirements (of the older, infirm and very young) that if an ETOPS aircraft had to div as a result of pressurization loss, and decend to a suitable level, it may not be possible to save all pax as a direct result of hypoxia and or hypothermia. Then again I am probably talking crap, but interesting none the less!
Either way, Cabin depress whilst on ETOPS or far away from the nearest diversion sends quite a shiver down my spine.... Very much as Cabin fire absolutely terrifies me as well. As a quick question to the cibvvies, do any of your drills for cabin fire include reducing speed and popping open doors or even jettisoning doors to assist in smoke elimination? I am led to believe having two doors open ( both at the rear) doesn half clear smoke quickly due to the "Chimney" effect of the airflow.