He unavailable - DeepAir again?

[JonG1]

Seldom, in these discussions pertaining to using He mixtures for dives to Deep Air depths, is mentioned the risk of helium bends. Personally, if I still dived beyond 130 ffw, or if I ever return to diving below 130 ffw, I wouldn't hesitate to work back to diving air to ~165 ffw. I used to be able to tolerate the nitrogen narcosis from air at that depth (and deeper). And with deep air, there is no risk of helium bends (which can be much more debilitating than nitrogen bends, I understand).

FWIW.

rx7diver

Is that still current thinking, I thought I'd read that helium is rarely the cause of the bend due to its low density, meaning that the inert gas causing the issue is usually n2 and the profile is the likely cause of treatment issues.

Might have misremembered tho

 

[tomsch]

Is that still current thinking, I thought I'd read that helium is rarely the cause of the bend due to its low density, meaning that the inert gas causing the issue is usually n2 and the profile is the likely cause of treatment issues.

Might have misremembered tho

As far as I know there is not more or less risk of getting bends when diving with helium. The only problem is that your deco times will be longer(helium penalty) due to a around 2.65x lower half-time of He in comparison to N2.

Edit: lower halftime not higher

 

[inquis]

your deco times will be longer(helium penalty) due to a around 2.65x higher half-time of He in comparison to N2.

The half-times are actually shorter for helium leading to higher tissue loading for each gas (partial pressure) for a given dive time. The M-Values are also higher, but not so high that they don't increase the total deco time. On ascent, you have to stop deeper than you would without He. This additional time at depth increases N2 loading and lengthens total deco time.

 

[tursiops]

I wasn’t there at the time.

Shouldn’t we save a collection of these articles for fun reading?

On the other hand, if ever a book needed to be burned.....

 

[rx7diver]

Is that still current thinking, I thought I'd read that helium is rarely the cause of the bend due to its low density, meaning that the inert gas causing the issue is usually n2 and the profile is the likely cause of treatment issues.

Might have misremembered tho

@JonG1,

My lay understanding (from a while ago) is that helium more easily winds up in smaller places much more quickly. And that it more readily comes out of solution. There are significant implications. For example, there is an increased risk of spinal cord injuries, inner ear injuries, and eye injuries. As another example, a 60 fpm ascent rate can be tolerated (per your dive tables or dive schedule) when diving deep air, but such a fast ascent rate from a helium dive is extremely risky.

Again, this is my understanding from a number of years ago. If there is more current information about this, I hope someone will let me know.

rx7diver

 

[PfcAJ]

Bakers dozen (by JJ) for computers was correct 20 years ago. It’s mostly correct today.

Bakers dozen (by George) for 80% was correct 20 years ago. It’s still correct today.

 

[rjack321]

Is that still current thinking, I thought I'd read that helium is rarely the cause of the bend due to its low density, meaning that the inert gas causing the issue is usually n2 and the profile is the likely cause of treatment issues.

Might have misremembered tho

There's an old paper out there (formerly on the Rubicon site) which badly bent some rabbits and then measured "what's in a DCS bubble". You're basically correct, its disproportionately N2 not helium compared to the initial breathing gas mix. I don't have the author or the year anymore and Rubicon seems to shut down anyway.

 

[PfcAJ]

There's an old paper out there (formerly on the Rubicon site) which badly bent some rabbits and then measured "what's in a DCS bubble". You're basically correct, its disproportionately N2 not helium compared to the initial breathing gas mix. I don't have the author or the year anymore and Rubicon seems to shut down anyway.

And this really makes a lot of sense as helium has significantly lower solubility than nitrogen.

 

[wetb4igetinthewater]

I think it's kinda comical listening to people get all worked up about an article written 20 years ago as if it's something new.

p.s. the subject of the author, his actual affiliations, and his method of delivery has been addressed multiple, multiple, multiple times here.

I think we should all be grateful that GI3 was engaged in a niche sport instead of being the US ambassador to the Soviet Union. Only cockroaches would be alive right now.

It's all about perspective people.

EDIT: I stand corrected: 8 Animals That Would Happily Survive A Nuclear War

 

[tomsch]

The half-times are actually shorter for helium leading to higher tissue loading for each gas (partial pressure) for a given dive time. The M-Values are also higher, but not so high that they don't increase the total deco time. On ascent, you have to stop deeper than you would without He. This additional time at depth increases N2 loading and lengthens total deco time.

Sorry, my fault, meant lower times but wrote higher. Max halftime on N2 is around 600-700 min for ZHL 16 while He has max around 260 min