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diverrick · Jun 5, 2005

I was out at a local airport the other day and got into a conversation with someone who was skydiving from very high altitudes from an unpressurized aircraft. He was telling me that they have to breath pure oxygen before they jump, "due to the chances of them getting bent on the way down". I don't get this, as they would be falling to HIGHER pressure, plus they are not breathing compressed nitrogen to begin with. The oxygen I am sure helps keep them mentally sharp at the rarified altitudes they were going to, but I don't get all this stuff about getting bent while free falling. Plus the pressure change would have to something less than one atmosphere (14.7) a very slight pressure change in all. Any one know the answer for sure?

pt40fathoms · Jun 5, 2005

He mis-spoke, or was misunderstood. The DCS hit will come as a result of the depressurization of the aircraft.

We would pre-breath for 30 minutes prior to depressurization, and while on descent until we reach a safe altitude and can breath air.

pasley · Jun 5, 2005

I agree. The culprit is the assent, not the decent, and perhaps the very thin air lacking sufficient Oxygen to sustain them in a coherent mode.

But this is a question for DocDeco. The astronauts have to worry about the bends, buth that is because they are going from 1ATA to 0 ATA when they do ther space walks (it appears the shuttle offers a presurized cabin.

pusser · Jun 5, 2005

pasley:
I agree. The culprit is the assent, not the decent, and perhaps the very thin air lacking sufficient Oxygen to sustain them in a coherent mode.

But this is a question for DocDeco. The astronauts have to worry about the bends, buth that is because they are going from 1ATA to 0 ATA when they do ther space walks (it appears the shuttle offers a presurized cabin.

I believe astronaughts use a 1/4 ata pressure in the space suit on pure O2. They have to go though a deco profile of some sort before donning the suit This gives a po2 of .25 and a lot less pressure on the suit.

pcowboy6196 · Jun 5, 2005

The oxygen is to keep from getting hypoxia. At those altitudes oxygen is extremely thin. At 45k feet and no oxygen there is only 1-3 minutes of useful consciousness. and oxygen does help from getting the bends because you are saturation your cells with oxygen and essentially purging all the nitrogen out of your system. I recently did a rapid decompression to 42K and you have to get an oxygen mask on immediately and not hold your breath. oxygen to keep from passing out and holding your breath during a rapid decompression will cause devastating lung over expansion just as in diving.

wedivebc · Jun 5, 2005

pcowboy6196:
The oxygen is to keep from getting hypoxia. At those altitudes oxygen is extremely thin. At 45k feet and no oxygen there is only 1-3 minutes of useful consciousness. and oxygen does help from getting the bends because you are saturation your cells with oxygen and essentially purging all the nitrogen out of your system. I recently did a rapid decompression to 42K and you have to get an oxygen mask on immediately and not hold your breath. oxygen to keep from passing out and holding your breath during a rapid decompression will cause devastating lung over expansion just as in diving.

If you are jumping out of a plane you are rapidly going from a low N2 atmosphere to a higher one. Bends are a result of the opposite. O2 would only reduce the N2 at high altitude.

diverrick · Jun 5, 2005

Ok you all seem to be in agreement that either he was a bit confused, or I misunderstood. Thanks for the prompt responses. BTW I won't jump out a perfectly good airplane. but I will out of a perfectly good diveboat.

pcowboy6196 · Jun 6, 2005

wedivebc:
If you are jumping out of a plane you are rapidly going from a low N2 atmosphere to a higher one. Bends are a result of the opposite. O2 would only reduce the N2 at high altitude.

Yes indeed. If you are flying in a de-pressurized aircraft to that height you will start breathing oxygen before takeoff to purge you body of any nitrogen. Im not a sky diver but i am pretty sure that they will continue to breath oxygen until they decend to much lower altitude. I only speak from what i learned of flight phisiology during aircrew training. Yes oxygen will only help from getting dcs during a rapid decompression. I must have not worded it right.

david.tolan · Jun 7, 2005

1) You can suffer a bend on ASCENT. So you pre-breath O2. We didn't need to for a jump at 23000'. It's going to depend on Altitude, and the rate you get there, and possibly on how long you spend there.

2) You need O2 above 18000' to stay with the world, unless you spend weeks aclimitising.(sp?)

I did jump, a lot. Kinda got bored with sitting around waiting for good weather, (Ireland), When there was wall to wall cloud, we use to do hop & pops. Go to cloud base, 2000' was fine, get out, clear the aircraft and open. That's WAY more interesting than going high. You can see individual people on the ground. It's personal. At 23K it's more like a photograph.

Blues Skies,
Soft Landings.

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