Originally Posted by
Aztec Kid
Pilots are often surprised that the duration of oxygen available for protective breathing is quite limited. This is because the oxygen consumption rate for smoke protection is far greater than the supplemental oxygen required for a decompression event.
Per FAR 121.337 (relating to protective breathing equipment) the flight crew is required to have a 15 minute supply at a cabin altitude of 8,000’. This amounts to 300 liters per flight crewmember. The 660 liter requirement for two crewmembers is only for 15 minutes of protection. It probably includes an additional 10 percent reserve to account for possible mask leakage when operating in the emergency mode (100 percent with positive pressure).
Based on Table 1, with a full 3150 liter bottle, and 2 pilots, you will have 1 hour and 12 minutes of oxygen.
3150/(660*4) = 3150/2640 = 1.19 hours = 1 hour and 12 minutes
If you have 4 pilots on the flight deck, you only will have approximately 36 minutes.
Keep in mind that this protection from smoke and fumes is available to the flight deck crew. The only protection available for the cabin crew is by the PBE. The passengers have no protection. The passenger oxygen masks are only designed to address a decompression event.
This underscores the need to eliminate the source of the smoke or fumes as soon as possible.
Thanks very much for your answer.
But Boeing gives us a particular information below table 3 (see above the sentence) that we could translate by a "real" O2 consumption, in this case, for extensive utilisation at 100%, 13 L/pilot/min., which is less than the 22 issued from regulation (300 L + 10% of potential leakakes per pilot). My initial question looked for a real endurance iso a required one.