Advanced Gas Switching

[rjack321]

Total time on backgas is 2 minutes, 30 seconds of which was moving up to the next stop. If you double the time to stow, a "new diver" would be on backgas for 3 minutes and that really is inconsequential in the grand scheme of things, certainly not enough IMO to cause worry about ICD since you aren't intaking that much He.

Not to mention IBCD doesnt actually exist for deco, and certainly not at 20ft.
If you want to do a trimix to air switch at 220ft sure, probable problem
But you are far far more likely to take an inner ear hit on the O2 than have your 100% gas break gas cause ICBD

Keep your ENDs reasonable and ICBD is totally irrelevant. If Ross hadn't made that stupid "N2" warning in VPM years ago it would have faded into obscurity where it belongs.

 

[Manatee Diver]

@rjack321 "Inner ear hit on O2"

Can you explain I've never heard about that?

 

[rjack321]

@rjack321 "Inner ear hit on O2"

Can you explain I've never heard about that?

Also known as vestibular DCS
Pathophysiology of inner ear decompression sickness: potential role of the persistent foramen ovale - PubMed


Selective vulnerability of the inner ear to decompression sickness in divers with right-to-left shunt: the role of tissue gas supersaturation - PubMed

 

[rjack321]

Also Inner ear decompression sickness in compressed-air diving - PubMed

In water DCS due to a PFO or pulmonary shunt is a big risk factor for IE DCS and it ends up manifesting during shallow stops. The switch to O2 seems to be a risky time - although I dont have a huge cohort of cases everyone I know with an IE DCS hit (N=4) manifested at 20ft shortly after the first switch to O2.

 

[Graeme Fraser]

Now for the really stupid question: What is ICD?

Isobaric Counter Diffusion

https://www.google.com/url?sa=t&sou...FjAPegQIAxAB&usg=AOvVaw0HxrAik-VnPnA6n1TtJ3m8

 

[KenGordon]

When would you use the long hose, rather than just give the bailed out diver your cylinder? That sounds like a REALLY bad day...

I want to be left with bailout for me and that cylinder is plumbed into my BOV.
For simple single bailout dives that cylinder might be my suit gas too.

Worst I have had to manage is four bailouts at once when my intermediate bailout gas reg failed on my last mod3 course dive. I ended up with two on each side and it was slow and cumbersome but not a terrible issue.

For the gas changes I don’t really see the difference between a bailout ascent and a regular OC ascent. For two OC deco gases I was taught to switch from one to the other and I can’t really see the benefit of this going back to backgas game. I will try to ask an expert the next time one is available.

One of the key takeaways from mod3 for me was that you reach a point in depth/time where you need support divers or some other means to provide enough gas with certainty of getting that gas. It is extremely rare that I get to do stuff past 60 as those sites are generally a holiday week away and I have to be dived up at that sort of level first, which is not entirely trivial.

 

[rjack321]

When would you use the long hose, rather than just give the bailed out diver your cylinder? That sounds like a REALLY bad day...

Because:
1) you maintain eye contact with the bailed out diver - they need your presence of mind right now and not to be alone
2) you can manage their ascent and additional switches keeping the ascent reasonable and verifying their switches cause they won't be following proper protocols, they will leave dead regs hanging or fail to switch their computer or switch to the wrong gas or run out of gas again
3) if they have burned though their entire BO I can guarantee they are going to keep making mistakes and unforced errors

You pass them a bottle and
1) there's a non-zero chance of dropping it
2) you are not being a responsible buddy - they need more than gas

Every person who has bailed on me has made at least one more significant mistake between the moment of bailing and the surface and those weren't even very deep BOs (<50m) or very long ascents (<30mins).

 

[JonG1]

I've bailed twice for real, once in a simple quarry environment and once in a mine.

Both times despite being self sufficient throughout I missed key steps, such as computer switches.

I can only imagine that if you got to the point of needing to take a bottle from someone else it could go south very quickly and inc the task load unnecessarily.

Before I had to bail I used to think passing off would be better, not anymore!

Everything slows down when it goes wrong, well it does for me, I ran out of suit gas on Sunday and it took an eternity to remember I had a whip on 1 bailout to switch to.

 

[rjack321]

=
Everything slows down when it goes wrong, well it does for me, I ran out of suit gas on Sunday and it took an eternity to remember I had a whip on 1 bailout to switch to.

Wow when the poo hits the rotating thingie for me I tend to rush like crazy (and rushing = screw ups)

 

[CptTightPants21]

Wow when the poo hits the rotating thingie for me I tend to rush like crazy (and rushing = screw ups)

Some people are angry drunks and some are super mellow drunks. Going too fast and going too slow are caused by the same thing-your mind has gone blank and you've stopped thinking.