Drawbacks to Helium??

[kanonfodr]

Looking through various agency's standards for diver qualification, it seems to me that some agencies are a little gun-shy of giving divers access to Helium, and quantities of it at certain levels (eg. TDI's AN/DP Helitrox add-on that limits mixes to 20% He) while other agencies are far more liberal with Helium for dives on the same level (eg. GUE Tech1 certifying for 21/35) and some of these additions have been recent (TDI) while other programs involving Helium have been established longer.

Why is this? Why do some agencies keep He levels low, while others want it early, often, and in larger amounts? Is there some danger to using elevated fractions of Helium that beginning technical divers may not be ready to handle? I'd really like to understand the difference between agency's motives.

Peace,
Greg

 

[rjack321]

"Motives" might be a bit strong. Helium is a much misunderstood (and longterm somewhat still experiemental) and some of these misunderstandings shape current course offerings.

Some agencies think beginning technical divers can and will screw up and try to "protect" them with low helium contents. As a general rule these agencies tend to have vague and pretty generous standards (i.e. although individual instructors may be quite rigorous the agency's themselves are not)

Other instructors/agencies provisional far more student's and make them come back for remedial skills work because they expect you to deco dive at a high level regardless of whether you're a beginner or not. These latter agencies tend to have stricter standards and cards issued by them include helium earlier in their training progressions and in more liberal amounts.

 

[DevonDiver]

Helium is a gnarly gas when it comes to decompression. I guess that some agencies what to increase the amount used incrementally, to ensure that the diver concerned has time and experience to develop their skills in line with the requirements of using the higher % gas.

Other agencies establish a very high skill baseline for initial entry into He diving. Confident in the diver's skills, they can load up the % from the start.

 

[Kern]

Just how factual are some of the well known facts about the dangers of He?

 

[rjack321]

Just how factual are some of the well known facts about the dangers of He?

They aren't "facts" they are urban myths...

For instance the perception that "helium will bend you" for ascent violations worse than air is not accurate. Bubbles are disproportionately made up of N2 after explosive (trimix) decompression.
Rubicon Research Repository: Item 123456789/2613

 

[ajduplessis]

It's the same with PPO2 levels. Some agencies have different levels for diving, ranging from 1.2 to 2. Each has their own reason in determining “safe” partial pressures and the same happens with Helium in reducing narcosis. Some accept a PPN2 of 3, others 3.5 and higher and this is where I believe the higher/lower % of helium is derived from.

My 2 cents.

 

[Kern]

They aren't "facts" they are urban myths...

For instance the perception that "helium will bend you" for ascent violations worse than air is not accurate. Bubbles are disproportionately made up of N2 after explosive (trimix) decompression.
Rubicon Research Repository: Item 123456789/2613

When I say, "well known fact," I'm being a wee bit sarcastic.

My definition of a "well known fact" is similar to that of Terry Pratchett; Baseless nonsense, propagated by those who don't know, but repeated so often, that those who do know, will never convince them otherwise. In other words, & as you say, an urban myth.

The diving world is full of them.

PS. Thanx for propagating the "actual facts" though.

 

[w ripley]

If you want to have a really good laugh, do a little digging on how the various agencies reacted to Nitrox. It wasn't that long ago that Nitrox was considered voodoo gas by more of the agencies than you might guess.

 

[Akimbo]

Comparatively speaking, there is very little quantitative data available on Trimix decompression. The world's Navies, who perform the great body of human testing, have a long history with HeO2 mixtures, as does the more proprietary oriented commercial diving industry. The comparatively narrow depth range where Trimix offers minimal thermal and economic advantages does not justify the costs to the organizations with the money to prove the tissue theories.

Understandably, there is a lot of well informed scientific speculation/unproven theory — a necessary phase in the pursuit of knowledge. This conundrum always results in uniformed speculation and urban myth. This problem is not likely to improve anytime soon because so much of the commercial diving industry is moving toward full saturation where decompression is very well proven, has an extremely low incident of DCS or other complications, and the tables are so simple they can be memorized in a few minutes.

 

[Blackwood]

eg. GUE Tech1 certifying for 21/35

And 18/45 too.