My AN/DP/Helitrox course

[rjack321]

Just curious, I ended up doing my helitrox course (I didn't have an inflator bottle), but with only 20% helium in the mix. I didn't feel cold, and I didnt notice any difference in clarity at depth.

how cold was the water?
you can get away with a lot in warm water (and 20% helium)
but that class doesn't exactly have long decos either

 

[Graeme Fraser]

I also only use 25% He and above for trimix fills and wouldn't use it for suit inflation. Most of our 45m plus sites are cold enough without making it worse with chilly gas.

However, when on trimix, I tend to plug into my lean mix rather than a dedicated suit inflation cylinder.

 

[Marie13]

I was told that for a mix over 20% He, you need a suit bottle.

 

[Graeme Fraser]

I was told that for a mix over 20% He, you need a suit bottle.

I can't say for TDI. My trimix courses we're through PSAI.

 

[Marie13]

I can't say for TDI. My trimix courses we're through PSAI.

I don’t actually remember if that’s in the course materials. That’s what instructor told me, as well as a couple of other local divers (TDI trained, I believe).

 

[rddvet]

How much helium do you guys put in the mix before going to an inflator bottle? Is there a threshold where you actually start noticing a difference?

I understand helium is a poor insulator and air is cheaper to use than the minimum amount of back gas with trimix.

I was taught anything over 20% use alternative suit gas or up to 25% if you’re really cold tolerant and the waters not very cold.

 

[Scuba Cobra]

how cold was the water?
you can get away with a lot in warm water (and 20% helium)
but that class doesn't exactly have long decos either

Water was in the low 70's, but I get cold easily.

I ask because the course may not have long deco obligations, but I sure am racking up [relatively] long deco out diving with my buddies.

I was taught anything over 20% use alternative suit gas or up to 25% if you’re really cold tolerant and the waters not very cold.

Thanks. That's roughly what my instructor had said with the caveat Rjack had mentioned early about vasoconstriction and getting bent easier. The TDI book was kind of less than helpful for a black and white answer.

 

[RainPilot]

Yeah a definitive answer won’t be forthcoming when it comes to any exposure protection. There’s way too much variation in personal tolerance etc.

We know the extreme edge cases but where exactly the line is will never be known. A lot like deco theory.
Personally I don’t use any trimix for a DS but that’s mostly because I am on CCR so I am not inflating off my diluent anyway. I generally find my leanest deco bottle to be most useful.

 

[arthurng311]

I was diving virgin wrecks in coron Philippines on a drysuit when my suit inflation bottle failed and i couldnt replace one, water temperature was 28C at 60m, I had a dive time of around 105 minutes with 30 minutes of bottom time. As a last resort i pumped 15/55 into my drysuit during that expedition, and honestly i couldn't tell the difference. I guess you can get away with an awful lot in warm water, YMMV.

 

[Scuba Cobra]

I hope I'm not hijacking too much @Marie13.

Are there any studies that show an increase in likelihood to get a type 1/2 DCS hit by using TMX for DS inflation?