skydiving oxygen system legality?

[billvon 2,400]

> my point was you must first be saturated.

You are. You are 100% saturated - at sea level pressures.

>going in a plane decreases pressure . . . .

Right. You have decreased pressure BELOW the point at which you are saturated - so you will start outgassing. If you can't outgas fast enough you can get DCS.

>so breathing compressed air will not increase your risk of getting bent.

In no case do you breathe compressed air in an airplane.

[LouDiamond 1]

A thread that touches on this subject can be found HERE.

A search on "oxygen" using my user name will also bring up many posts on the associated equipment and the draw backs to typical civilian skydiving O2 set ups.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[PiLFy 0]

"so breathing compressed air will not increase your risk of getting bent."

WTF?!

[mjosparky 3]

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A thread that touches on this subject can be found HERE.

A search on "oxygen" using my user name will also bring up many posts on the associated equipment and the draw backs to typical civilian skydiving O2 set ups.

One thing that skydivers don’t understand it how breathing at altitude is tied to pressure. The exchange of O2 and CO2 is all done in the alveoli, the little sacks in the lungs. In order for this exchange to take place there has to be enough pressure for the O2 to pass through the alveolar membrane. At sea level the pressure of the O2 in your blood is about 100mm Hg. At 15,000 feet it is down to 44mm Hg and your situation is about 80%. Anything below 87% is considered hypoxic. From about 18,000/20,000 feet up to 40,000 feet you can breathe pure O2 and still be hypoxic. This is where you should be on a diluter-demand system to maintain the pressure needed to ventilate the alveoli.

Sparky

My idea of a fair fight is clubbing baby seals

[pchapman 261]

Hang on. I've seen all sorts of varying numbers for altitudes. But I've seen it written that Constant Flow is OK to 30,000', Diluter-Demand to 33,000', and Positive Pressure above that level, since above that level one would be getting hypoxic even with 100% oxygen at the ambient pressure. But as I said, the numbers tossed around vary a lot.

In a way, diluter-demand is only a way of saving on oxygen flow, not really improving on the physiology. That's why one can do constant flow up to quite a high altitude, if one can afford to be wasteful about oxygen. However, you are right that diluter-demand is superior IF one is talking about certain mask designs.

So for example even if you crank up the oxygen flow, at some point having a cannula, small hose in one's mouth, or a mask with holes is not enough. When you breathe in, you suddenly need a larger volume of air, so that can't be supplied all of a sudden from the fixed rate of oxygen from the little hose. You either suck the air in from outside too (not desirable if too high), or you need a bag attached to the mask which holds either oxygen or an air-oxygen mix -- or you use diluter-demand which can supply a larger volume of air & oxygen when combined with a large diameter hose (fighter pilot style).

So there is also a large difference in mask types, not just the regulators used. Masks can have open ports, they can have simple partial valve systems, they can have full valve systems, they can have a non-rebreather storage bag, or they can have a rebreather bag. Some systems are fine to a certain altitude, above which a more sophisticated system is needed to provide more oxygen in the mix.

I'm not explaining all the details here, just making the point for this thread in general, that there are some additional complexities.

[LouDiamond 1]

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So for example even if you crank up the oxygen flow, at some point having a cannula, small hose in one's mouth, or a mask with holes is not enough.

As you stated, it is not enough. Using this method is the norm in civilian skydiving but is really only good at barely staving off hypoxia at lower levels. What people fail to realize is that any system where you can breath O2 AND ambient air above 18k ft is pretty much worthless as you have not purged and or are still introducing nitrogen into your blood stream. Hypoxia is just one of the issues to be concerned about, DCS is also a very serious one to be concerned about but often not discussed or known. The only solution is a full face mask with a constant seal ( not taking it away from your face) and prebreathing for the correct time to purge the nitrogen from your system.

Pressure breathing and diluter demand accomplish the same thing just in a different manner. The newer systems use the later as pressure breathing is only good if you have a constant supply which usually means you are hooked up to a console of some kind, it also makes communicating/talking just about impossible. Imagine every time you opened your mouth or breathed in it felt like a someone was shooting a firehose of air into your lungs, it's not fun at all.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[billvon 2,400]

>From about 18,000/20,000 feet up to 40,000 feet you can breathe pure O2 and still be hypoxic.

You can always be hypoxic for a number of reasons - lung problems, breathing problems etc. But if you are breathing 100% O2 at 20,000 feet or even 36,000 feet, the partial pressure of oxygen is HIGHER than it is at sea level.

(Math - sea level, 14.7psi, 20% oxygen -> partial pressure O2 is 3psi. 20,000 feet, 6.7psi, 100% oxygen -> partial pressure O2 is 6.7psi. 36,000 feet, 3.3psi, 100% oxygen -> partial pressure O2 is 3.3psi. Above that even pure O2 doesn't get you back to 3psi.)

That does not mean that there's no problems of course. Outgassing of nitrogen can cause DCS, which is why you have to prebreathe - and system leakage can effectively reduce O2 concentration.