Oxygen Time for B777 pilots

[Philemon]

Hello everyone,

As instructor, I try to obtain a good idea about how many time in 100% O2 mode (in protective breathing situation) have 2 B777 pilots with a full O2 bottle of 3150 liters at 1850 PSI. Does anybody know how to calculate that with the B777 PD tables ? Thanks a lot in advance…
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[cavuman1]

Bonjour, Monsieur Philemon! As a sufferer of Chronic Obstructive Pulmonary Disease (COPD), I have been tethered to cannulated oxygen for twelve years. Though annoying, it beats the heck out of the alternatives! Here are a couple of articles which I hope will help you find the answer to your question: O2 Tank Depletion Rates Oxygen Tank Size Duration Bon Chance, Mon Ami!

- Edvard

[Musician]

Table 3, 2 crew, up to 13999 ft, 100%, gives 22 l/min
3150 l / 22 l/min = 143 min = 2:23 hours.

At higher pressure altitudes, the air is less dense, so 100% requires less oxygen, and endurance is longer.

The Table 3 note suggests that at 8000 ft the rate should be 26 l/min.

[Philemon]

So, for you, the consumption of the 22 L/p/min. from Table 2 (altitude below 14 000 ft alt. pressure) is for 2 pilots and not for only one, that is to say 11 L/P/min ?

Also, about the « note », do you think that we must add the figure of 13 L/p/min to the 11 L/p/min. of Table 2 (new consumption : 11 + 13 = 24 L/p/min.) or this first consumption (13) replaces completely the latter (11) ?

Tks again…

[Musician]

Originally Posted by Philemon

So, for you, the consumption of the 22 L/p/min. from Table 2 (altitude below 14 000 ft alt. pressure) is for 2 pilots and not for only one, that is to say 11 L/P/min ?

Yes. The table shows 33 l/min for 3 crew and 44 l/min for 4 crew, so it's clearly 11 l/min per person at that altitude.

Also, about the « note », do you think that we must add the figure of 13 L/p/min to the 11 L/p/min. of Table 2 (new consumption : 11 + 13 = 24 L/p/min.) or this first consumption (13) replaces completely the latter (11) ?

Table 3 gives what needs to be added to the table 2 value for extra time. I understand the "add" in the note the same way. If you read it as "add to table 3", that would more than double the oxygen requirement, and that feels implausible, and would far exceed the air density difference? But I could be wrong on that, so hopefully someone else knows better.

[cavuman1]

For comparison, to maintain a >94% blood oxygenation for my medical needs (staying conscious and alive!) at 607' ASL, I breathe 1.5 liters/min. of 95% pure oxygen. The gas is supplied by a concentrator which utilizes a zeolite molecular sieve. I used to need 4 l/m, but when I was hospitalized for a cardiac arrhythmia two years ago, I was treated with BiPAP: BiLevel Positive Airway Pressure. This therapy opened some of the cigarette-clogged alveoli in my poor old lungs, resulting in a much improved oxygen requirement. Lord knows I rue the day I took up smoking. It took forty-eight years for me to put those "health tubes" down. The Grim Reaper was in the room and he was walking directly toward me! Rapidly!

- Ed

[Musician]

Originally Posted by cavuman1

For comparison, to maintain a >94% blood oxygenation for my medical needs (staying conscious and alive!) at 607' ASL, I breathe 1.5 liters/min. of 95% pure oxygen.

Yeah, that's essentially "normal mode", where the oxygen is added to the outside air. That's not sufficient when that air is toxic (smoke etc.).

[Musician]

https://pros-blog.padi.com/dan-safet...-aid-prepared/ says 100% oxygen for a diver is a "flow rate of at least 10-15 litres per minute (lpm)".
24 lpm would clearly be too much.

Actual oxygen consumption obviously depends on the physique of the person, big people need more than small people, etc.

[Philemon]

Thanks again for this precision that gives me more arguments... 👍

[cavuman1]

As an aside, patients in acute pulmonary failure can be administered as much as 60 (sixty) liters/min!

- Ed

[Philemon]

My big interrogation now concerns the sentence beginning by "add" : for a consumption at 100% in an extensive utlisation, must we "add" 13 L/pilot/min. to 11 L/pilot/min. (i.e. 24 L/pilot/min. total) or simply "replace" 11 L/pilot/min. by 13 L/pilot/min. ? Because the time available per pilot won't of course be the same...

[VH_WTF]

As an aside, patients in acute pulmonary failure can be administered as much as 60 (sixty) liters/min!

Yes but for the drivers at home(or up the front) that's not because they consume that much, only to create a steeper pressure gradient and force more o2 across into the bloodstream when uptake capacity is dramatically reduced.

must we "add" 13 L/pilot/min. to 11 L/pilot/min. (i.e. 24 L/pilot/min. total) or simply "replace

Replace.

Exesss o2 intake is best avoided and is harmful also. Look up oxygen toxicity.

[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.

[Philemon]

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.