Why is the max depth of Helitrox 150ft, while air goes to 180ft???????

[Tigerpaw]

Helitrox has a max depth of 150ft while Extended Range (Air) has a max depth of 180ft. Since Helitrox is a Helium Oxygen blend with a 100% O2 deco gas why is the depth limited to 150ft? Why isn't it 180ft or even 200ft? Just curious.
And for those wondering, NO I will NOT be doing Extended Range on air. Many thanks.

 

[Whitrzac]

Because diving air to 180ft is dumb, but 'is the way things use to be done' so somehow it sticks around. Like an STD you cant get rid of.

 

[jborg]

One is for those who care about narcosis and gas density, the other is for those who don't.

 

[inquis]

Helitrox is a Helium Oxygen blend

That blend would be heliox. Helitrox has nitrogen and is basically trimix with a limited amount of He (e.g., 20/35)

 

[broncobowsher]

Because Helium is expensive?

The deep air people I know are old school, and generally old as well. 150 on air is far enough for me. Even then I want good conditions to even try it. But really if I am planning on that, the rebreather is just going to get used (with Helium).

I have not kept up with any of the training agencies rules/levels/guidelines in near a decade now. I am sure they have changed. I just saw something about O2 exposure has changed. But the universe didn't change.

 

[randini]

I think it has more to do with the idea that the helitrox is an alternative to deco procedures. Helitrox is trimix with training wheels, only 1 deco bottle and up to 32% He. It's not 200ft because that's the territory of the normoxic trimix course.

Extended range is deeper because it teaches the diver to handle two deco bottles, like in the trimix course.

 

[tursiops]

TDI Helitrox: "The Helitrox course examines the theory, methods, and procedures for planned stage decompression diving utilizing Helium in the breathing mixture. This program is designed asa stand-alone course, or it may be taught in conjunction with TDI Advanced Nitrox at thediscretion of the instructor. The objective of this course is to train divers how to plan andconduct a standard staged decompression dive not exceeding a maximum depth of 45Metres/150 Feet. The most common equipment requirements, gear set-up, and decompression techniques are presented. Students are permitted to utilize Enriched Air Nitrox and Helium mixes with no greater than 35% He content, and up to 100% oxygen for decompression diving provided the gas mix is within their current certification level. Breathing gas mixtures containing more than 35% Helium (+/-5%) or less than 21%oxygen are not permitted (+/- 1%)."

TDI Extended Range: "This course provides training and experience required to competently utilize air for dives up to 55 Metres/180 Feet that requires staged decompression, utilizing nitrox mixtures oroxygen during decompression. The objective of this course is to train divers in the proper techniques, equipment requirements, and hazards of deep air diving to a maximum of 55Metres/180 Feet utilizing nitrox mixtures or oxygen for staged decompression."

I did the Extended Range class long ago. Final dive was to a wreck at 180 ft. I have no memory of the dive. Never again!

I would like to think we have gone beyond such stupid diving.....it was a bad idea 20 years ago, it is worse now that it is unnecessary. Yes, I understand that in some places you cannot get He and the dives are deep; that does not make the dive less stupid. Just don't do the dive.

 

[Nick_Radov]

You must have misunderstood. The maximum depth for air is 100ft / 30m.

 

[tursiops]

You must have misunderstood. The maximum depth for air is 100ft / 30m.

Ahhh, GUE vs TDI.......here we go!

 

[lowwall]

One is for those who care about narcosis and gas density, the other is for those who don't.

This is the actual answer.

TDI Helitrox originally had a max He component of 20%. At 45m, this gives an Equivalent Narcotic Depth (END) of 34m (112') on air.

TDI later increased the He max to 35%. Keeping the same END with 35% He would have allowed them to go to 57.6m, but by that time Anthony and Mitchell had published their recommendations on keeping gas density below 5.2 g/L. Conveniently for TDI, 45m is the deepest you can go (assuming 5m increments) with 21% O2 35% He without exceeding the recommended 5.2 g/L so they stuck with the same limit.

Performance Under Pressure

Gas density is one of the unknown mechanisms on the forefront of hyperbaric research.

dan.org