Mt. Everest of Diving

[Waterlover]

Irreversible asphyxiation will occur as a result of the rapid diffusion of the HE in the lung tissue. Basically the HE blocks the passage of Oxygen. Diving grade helium used for commercial diving usually has 2% O2 in to prevent this blocking of the oxygen and keep the O2 passage way open. They also use this gas for saturation diving. You cannot breathe pure helium for a few minutes. Maybe 3-6 breathes before you don't wake up. You need at least a PO2 of .16 to remain awake with the gas you are breathing.....Ken

 

[VTWarrenG]

The whole concept of pure helium seems pretty stupid.

1) The whole point of using specialized deco gasses is to help offgas either nitrogen or helium. The presence of oxygen does not adversely affect the offgassing except in the slight lessening of inert partial pressures -- and it usually helps to sustain life.

2) The body only needs a small fraction of oxygen (0.16 ATA), and thus there's really no reason to breathe pure helium.

3) Besides that, the minimal amount of time you can spend breathing a hypoxic gas would have little effect on one's deco. Toggling refers to taking breaks to back gas for 5 minutes. A one minute break to pure helium would serve basically no purpose, and would carry an inordinate and unnecessary amount of risk.

I have the feeling someone read something somewhere and misunderstood what they read. These divers are decoing on pure helium and oxygen -- NOT pure helium.

- Warren

 

[Stone]

Ken,

Originally posted by Waterlover
Basically the HE blocks the passage of Oxygen.

Does N2 act this way, too, or would the guys cleaning the fuel tanks last 2 or 3 minutes?

 

[VTWarrenG]

Waterlover,

2% O2 in to prevent this blocking of the oxygen and keep the O2 passage way open.

Uhhh... what exactly is the "oxygen passageway?" I've read up on plenty of anatomy and physiology, and never found this one. How does the diffusion of helium prevent the diffusion of oxygen? Even if this mysterious effect existed, don't you think the lack of oxygen in the breathing gas would be a more relevant cause of hypoxia than the closing of the oxygen passageway?

Maybe 3-6 breathes before you don't wake up.

The fact that pure helium asphyxiates has nothing to do with the fact that it's helium -- and everything to do with the fact that it's not oxygen. Any hypoxic gas will cause the same ultimate effect -- death. Most people can sustain consciousness for several minutes with no inspired oxygen.

- Warren

 

[Waterlover]

Pure nitrogen will diffuse slower in the tissue than pure helium(helium diffuses aprox 2.7 times faster than nitrogen). The helium will block the oxygen passage into the tissue. The oxygen will not displace the helium in the tissue. I agree Warren lack of Oxygen in the mix is what causes the loss of consciousness. My point is IMO I don't believe you can breathe pure helium on decompression without the helium blocking the passage of oxygen into the tissue. I could be wrong and I'd be interested in finding out why they used PURE HE as it is a major risk.. Ken

 

[VTWarrenG]

Waterlover,

Could you provide some references? I haven't ever heard the phrase "oxygen passageway" in the umpteen million documents I've read. It just seems rather irrelevant to me what effect helium has on oxygen diffusion... when there's no oxygen present to diffuse.

The concept that the He blocks the passage of oxygen into tissues is a completely foreign concept to me -- considering that gradient diffusion dictates the ongassing/offgassing of all gases in accordance with the relative partial pressures between the tissues and the inspired gases. Besides, if you're decoing, you're likely already at the saturation limits of your inert gases, and you likely won't ongas anymore inert gases at all, no matter what you breathe.

No one breathes pure helium, ever... I beg for some references! :boom:

- Warren

 

[Waterlover]

I am not at a place where I have my reference books. The CGA( Compressed Gas Assoc.) has a information on helium dangers. Also there are some other references in some of the tech diving books regarding pure helium.
I will send them to you when I get home and look them up. Also I agree no one breathes pure HE I am disputing that John Bennett did it on his deco(breathed pure helium) from his record setting dive. My point is that because there is no oxygen in his mix he would be rendered unconcsious. Also because it is pure helium it is impossible to revive someone even using 100% O2. The rapid diffusion of helium into the tissue is even faster than Oxygen thus O2 would not be able to get into(diffuse) the tissue. I have witnessed someone breathing10/50 trimix pass out after taking 6 breathes from the regulator while walking down the dock. He was revived using pure o2. If it was pure helium the lungs would have been saturated with helium and there would be no way to get the oxygen into his tissue, but because of the O2 in the mix they were not saturated with helium so there was a "passageway" to get o2 into the tissues.
Ken

 

[VTWarrenG]

Waterlover,

But see... you're still not explaining to me how this oxygen passageway mechanism works. How would rapid ongassing of helium prevent oxygen from being transported into the tissues? Science would have us believe that the partial pressure of helium in the tissues has nothing to do with partial pressure of oxygen in the tissues, and the diffusion of one is unrelated to the diffusion of the other. There may be something physiologically going on that I don't understand, but I think I'm rather clear on the physiology.

There are many people who breathe a few breaths of pure helium from balloons at frat parties -- these same people then go on to take a breath of air, and live -- so it seems their oxygen passageways are unaffected...

The man breathing 10/50 on the surface was a moron. But I don't believe his resuscitation was enabled by the 10% of O2 in his mix. I highly suspect that after he went unconscious, all one would have to do to save him would be to remove the reg from his mouth. Within a few [autonomous] breaths of air, he would have regained consciousness. I firmly believe that nothing would have been different if he were breathing pure helium. You're going to have to provide some stronger evidence than anecdotes to have me believe this oxygen passageway theory...

- Warren

 

[Waterlover]

I'll get the references for you(it will be a couple of days). Balloon helium has usually 20 -30 % O2 in it to prevent people from dying at Frat Parties also he'd be a dead moron had it been pure helium
Ken

 

[VTWarrenG]

Balloon helium has usually 20 -30 % O2 in it to prevent people from dying at Frat Parties

Is that so?

Seems pretty weird, then, that I've checked out at least three helium-tank rental sites, for example: http://www.balloonplace.com/helium.html

And they all make mention of the purity of their helium. They certainly don't seem to fill balloons with 30/70....

And I even called AirProducts (right next door to my building) and they're quite sure that no one ever uses heliox to fill balloons.

So I'm very perplexed.... I guess I'll just have to wait until you get me those references.

- Warren