TDI Helitrox

[rongoodman]

The question came up in Tri-Mix Agencies as to why TDI limits their Helitrox divers to 20% Helium, instead the 25% or 30% that some of the other agencies use for their Recreational Trimix classes. Any input from TDI? I thought it was a worthwhile addition to my Deco Procedures class, but I was wondering the same thing.

 

[dl348]

Ron, I thought only NAUI had a Helitrox class. I wasn't aware TDI had one also...it's not listed on the TDI website at least.

 

[rongoodman]

It's pretty new, just appeared this summer. I had booked my Adv Nitrox/Deco Procedures courses before I saw references to it here and over on Yorkshire Divers, so I contacted the shop and they had things straightened out with TDI by the time I got there in September. It allowed me to avoid the deep air dives that are normally done in those courses. There are dives up here that will go better for me with some helium in the mix until I complete Normoxic Trimix, such as the U-Boat off Block Island. IANTD has one too, and GUE used to, although I haven't heard much about it lately.

 

[TSandM]

GUE has morphed their class into their recreational curriculum as Rec 3. I'm not sure how many, if any folks have taken the class in its present incarnation.

 

[Troutmaster]

I have a TDI Helitrox card, and my understanding of the limit of 20% is this: They limit you to 150ft at that cert level, and 20% gives you a narcotic depth of about 100 ft at 150 actual depth.

 

[jago]

I'm not yet a Tx, Triox or helitrox diver but I know Helium need a very slow ascent speed. So Maybe TDI staff has considered than 20% of He would be the best compromise between narcosis and the risk of helium decompression sickness.

 

[SeaCobra]

NAUI's Helitrox class uses a training gas of 26/17 (17% He) and that is the reason. Gives the student a narcotic benefit without undue risk if ascent mistake is made.

Jeff

 

[Doppler]

The question came up in Tri-Mix Agencies as to why TDI limits their Helitrox divers to 20% Helium, instead the 25% or 30% that some of the other agencies use for their Recreational Trimix classes. Any input from TDI? I thought it was a worthwhile addition to my Deco Procedures class, but I was wondering the same thing.

Ambient pressure at 45 metres = 5.5 bar (that's about 150 feet and 5.5 ata)

using gas percentages from course guidelines...

Partial pressure of 20 percent helium in mix at 45 metres = 5.5 x 0.20 = 1.1 bar

Partial pressure of 25 percent oxygen in mix at 45 metres = 5.5 x 0.25 = 1.4 bar
Value of vacant partial pressure at 45 metres = 5.5 - 2.5 = 3 bar

Vacant partial pressure is filled with nitrogen therefore nitrogen narcotic loading at 45 metres is less than diving air to 30 metres (100 feet).

However, the tissue loading from helium at this depth and for bottom times that are practical at this level on open circuit, is very light and in a pinch a slightly modified, conservative "air" table can be employed if things go completely pear-shaped.

Good luck with the course.

 

[rongoodman]

Thanks for the reply. I did the course in September and had a great time.

 

[Blue Quaker]

Hi Steve,
When did the TDI Helitrox Course come into being? I can't find any info on it on the TDI website, and we've been teaching using our "IANTD hats" the TEK Lite program when students are looking for this type of course for the past couple of years as we didn't know it was available to teach though TDI.
Cheers,
Norman H.