Disturbing experience at dive shop

[Storker]

what's your 220 mix @kensuf ? 21/35?

21% O2 at 220'/67m is >1.6 bar pPO2. Isn't that somewhat on the hot side?
36% N2 at 220'/67m is an EAD of 35m/115'. Isn't that approaching narc country just a bit too much?

 

[rjack321]

18/40.

21% O2 at 220'/67m is >1.6 bar pPO2. Isn't that somewhat on the hot side?
36% N2 at 220'/67m is an EAD of 35m/115'. Isn't that approaching narc country just a bit too much?

lol @Storker there's a reason I asked...
None of the choices in this thread are my "go to" gasses. So I was curious even though I'm not doing 420ft dives, although I agree that another gas between 400 and 120 and a roughly 200ish switch makes sense. The 12/55 is probably the least useful option of all.
​

 

[jale]

21% O2 at 220'/67m is >1.6 bar pPO2. Isn't that somewhat on the hot side?
36% N2 at 220'/67m is an EAD of 35m/115'. Isn't that approaching narc country just a bit too much?

It is BO gas. How long you r going to stay at these values...
theory is good bur no need to follow blindly...

 

[kensuf]

It is BO gas. How long you r going to stay at these values...
theory is good bur no need to follow blindly...

I agree with you on the O2 % for non-overhead environments, if it spikes to 1.6, but you're going straight up, meh. Cave penetrations, hell no, O2 needs to be matched for the depth and time to exit.

Narcosis on the other hand, you need to minimize that. My first hand experience was from when we used to switch from trimix to air at 200' because we were scared of the helium (this was in the mid-90s) and that switch was like being kicked in the head by a mule. Coming off helium to deep END's is much more dramatic than descending on air the whole way down -- so if you think you're gonna be fine switching to a bailout with a deep END because you've been to 180 on air before, think again buddy because you're wrong.

 

[TrimixToo]

<snip>
It was after my buddy and I completed a very enjoyable deep dive and I ran some numbers on multideco did I begin to realise the impact if we had not challenged his gas substitution. He had substituted an intermediate deco mix of 32% nitrox with a trimix 12/55!!! (On what planet is that a sane choice?) This would have resulted in an additional 55 minutes on bailout and required 136 cuft of intermediate bailout gas vs 64cuft on my plan. We we carrying 80s so I would have needed an extra tank to make it home on bailout!
I have not spoken to the owner since I came to this realisation since that was my last day there and he was away from the shop the next day.
I want to talk to him about this as I consider him a friend but I am so puzzled and angry I don't even know where to begin. One of my first thoughts is that although he is an OC trimix instructor he may not actually have the CCR knowledge to understand what the consequences of his actions could have been. Can anyone experienced in CCR trimix suggest a plausible reason for making such a switch?

With some puzzlement, and considerable disappointment, unless it was somehow accidental ("My bad; I grabbed the wrong tank. Sorry, dude.") I'm afraid that would be my last-ever visit to that shop.

 

[stuartv]

Narcosis on the other hand, you need to minimize that. My first hand experience was from when we used to switch from trimix to air at 200' because we were scared of the helium (this was in the mid-90s) and that switch was like being kicked in the head by a mule. Coming off helium to deep END's is much more dramatic than descending on air the whole way down -- so if you think you're gonna be fine switching to a bailout with a deep END because you've been to 180 on air before, think again buddy because you're wrong.

Thank you for taking the time to share that. I can't speak for anyone else, but once again your experience and willingness to share here is helping me. Seriously. Thank you!

 

[jale]

I agree with you on the O2 % for non-overhead environments, if it spikes to 1.6, but you're going straight up, meh. Cave penetrations, hell no, O2 needs to be matched for the depth and time to exit.

Narcosis on the other hand, you need to minimize that. My first hand experience was from when we used to switch from trimix to air at 200' because we were scared of the helium (this was in the mid-90s) and that switch was like being kicked in the head by a mule. Coming off helium to deep END's is much more dramatic than descending on air the whole way down -- so if you think you're gonna be fine switching to a bailout with a deep END because you've been to 180 on air before, think again buddy because you're wrong.

Of course i do agree with you.
My remark was more about the general tendency which sees theories overriding reality.
Yes ppo2, narcosis, density, gas solubility, etc... are real factors to care about but it is always back to your personal risk management and to know where you draw your own red line considering your situation...

 

[sdj42]

BTW I did consider that the dive shop owner might have thought a switch from 10/70 to 32% might have been too extreme or he might just have been trying to sell more helium. I will talk to him about it at some point but thought I'd drop in here in case I'm missing something.

Unless you were on a different plan than everyone else that week, he was charging a flat rate per day by depth, so if there was a financial motivation for him it would've been to use less helium, not more.

I don't know what his gas choices were on his deep dive prior to yours to speak to his typical deep gas plan, since I was only involved in the first 200' or so of that one, but the fact that he lost one of his deep bailouts on that dive (and continued the dive anyway) may have gotten in his head somehow.

 

[Gareth J]

I’ve seen it twice, both on fit rebreather divers. My buddy is a triathlete, she does 3 or 4 a year.

Wookie

This has just been released by the BSAC

https://www.bsac.com/safety/diver-guidance-for-immersion-pulmonary-oedema-ipo/

New Guidance Released by BSAC on Immersion Pulmonary Oedema for Scuba Divers and Instructors


You might find it interesting reading. One of the areas they have been seeing/studying IPO is in the super fit - triathlon athletes!

Gareth

[Sorry if I'm deviating from the OP - move the thread if appropriate]

 

[Wookie]

Wookie

This has just been released by the BSAC

Diver Guidance for Immersion Pulmonary Oedema (IPO)

New Guidance Released by BSAC on Immersion Pulmonary Oedema for Scuba Divers and Instructors


You might find it interesting reading. One of the areas they have been seeing/studying IPO is in the super fit - triathlon athletes!

Gareth

[Sorry if I'm deviating from the OP - move the thread if appropriate]

DAN studied my crew member. You know of her. I don’t know if she was in the BSAC study.