Prevalence of Different mixes in side-mounted bailout bottles

[MattK911]

This tends to be popping up within the cave community. Typically as cave divers in Florida bailout is sidemounted with a matching mix, necklace on the left post, and longhose on the right post. All other gasses are carried in stage bottles that are dropped along the cave, and if doing mix dives, a suit inflation bottle is worn. I’ve now seen this with several sidewinder divers using trimix and for the life of me can not imagine why this is propitiating. Best guess is it’s all to avoid carrying an inflation bottle, or to save money on trimix.

There are several concerning problems with this configuration. One being Typically sidemount divers are driving the longhose off the right bottle. So in the event of an emergency at max depth you’d be donating a stupid rich gas with no helium? Or are you adding another long hose on you left bottle?
Or is everyone really just solo diving?

Can someone please explain WHO this stems from, and a legitimate reason for use?

Edit: post edited to narrow results to cave diving

 

[MattK911]

Paging @DiveTalkGus as he is 1 of 2 I’ve publicly seen talk about it. The other died in a cave diving accident, though unrelated to bailout choice.

 

[Whitrzac]

Are we talking deep ow, cave or deep cave?

By the time you need to donate gas to your ccr buddy you should have a handle on the situation. They should have gone through both of their bailouts.

Deep dives are al cylinders with 40in hoses that can be passed off as needed. lean left, rich right
Cave dives are a pair of lp50s at 3600(65cf) with matching bottom mixes. Long hose on one(your bottle) short on the other(my bottle) Extra gas and deco bottles staged as necessary.

 

[rddvet]

Hell no. It’s a very good way to kill yourself if one of them is a hypoxic mix (which is really the only reason someone would likely consider it). Even if you’re talking about 21 in one and 32 in the other, it’s still setting yourself up for eventual failure if you do move to a hypoxic mix.
Very dangerous imo
If you were talking a stage with a bottom mix for a small portion of the dove that’s a different story

 

[Whitrzac]

There is a much wider range of gear configurations and no standard for most things. It makes the prevdive talk/sdrill even more critical

 

[MattK911]

Are we talking deep ow, cave or deep cave?

I’m mainly referring to cave and deep cave, it’s where I’ve seen it occur. Seems to all be in an effort to avoid more stages, inflation bottles, and the cost of trimix

 

[Vicko]

You mean primary cylinders only?
On open circuit or as bailouts?
For bailouts of course, how else are you going to deco if you are doing something deep.

 

[grantctobin]

I’ve now seen this with several sidewinder divers and for the life of me can not imagine why this is propitiating. Best guess is it’s all to avoid carrying an inflation bottle, or to save money on trimix.

There are several concerning problems with this configuration. One being Typically sidemount divers are driving the longhose off the right bottle. So in the event of an emergency at max depth you’d be donating a stupid rich gas with no helium? Or are you adding another long hose on you left bottle?
Or is everyone really just solo diving?

Can someone please explain WHO this stems from, and a legitimate reason for use?

I've done it on holiday on a sidewinder in Bikini and Scapa. Zero penetration, open water, limited gas mix and bottle choices. Left bottle with 50% and a 40" hose tucked against the bottle, right bottle with 15/55 or 18/45 (or whatever silly mix Truk Master banks, 16/40?) on a long hose ran around my neck and under the loop.

I could see someone advocating for something like 32% in one side and 30/30 in the other in JB or Peacock, such that you get the gas density improvement/WOB/END decrease and to not have to figure out offboard inflation. An AL6 is simple enough that I don't bother and I just use a pair of 85s of 18/45 for almost any cave shallower than 190'.

I count 9 IANTD and 5 TDI Sidewinder Hypoxic instructors in the US, two of whom overlap both agencies. We'll add in a couple more from PSAI. I think only three or four of those individuals teach the class at least yearly and actively participate and teach "safe" extended range deep cave diving. The others...

It is an interesting conundrum in that there are very few public places in the US that someone could break 200' in a cave. Some in SW Florida, some near Tally, a few in Missouri. If we add Mexico, it gets a little bit easier to do so. Probably means we should be counting ART and or normoxic instructors, which increases the pool of "who teaches that it's safe to have mixes of different MOD on each side in an overhead on a sidewinder."

TLR. too little quality control. Long range deep cave diving on sidemount CCRs isn't for the faint of heart, and there's a lot of little things that need to be learned along the way to do it safely. It sure as **** starts with every instructor and team agreeing on PPO2 limits, bottle marking, END limits, gas density limits, etc etc.

 

[JonG1]

I do dissimilar sm in ow, 1 deep, 1 deco on normoxic wrecks, pretty much sop in the UK.

OHE though 2 identical sm bailouts with an appropriate mix.

 

[MattK911]

Post was edited to reflect CCR cave diving. I get carrying all bottles in OW, and I still just dive them as stages. 2 on the left chest, everything else on a leash, or more likely a tech rigged fathom