Standard Bailout Mixes

Decodiver

What I cited as an example is this:

All 3 cells 1.29 and you flush with a diluent that is 1.2 PPO2 at that depth, it tells you what?

Are all 3 of your cells so spot on that they are going to show 1.2?

Go to 90 metres and blow your loop full of O2, it takes more than 1 or 2 seconds to diluent flush that down to 1.3 believe me.

1 second for a diluent flush, Christ, your cells react fast.

Cheers,

Dave Cooper.

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Rebreather World Terms & Conditions

nigelh

<cough><splutter>
Isn't that back to front?

OK I date from that days when we were taught not to exceed 2bar ppO2 and 1.6 was preferred but even then you were supposed to tighten that up if working hard.

Breathing 0.21bar of O2 the ol' oxymeter shows 98% hemoglobin saturation. We only use higher rating because it's better than breathing inerts. I don't think higher O2 levels help any part of your body unless something else is severely compromised.

If I'm bailing out I'll risk being a little bent but I'm not messing with O2. That's just not life expectancy.

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nigelh

jradomski

The cells may take longer than that to react.. but I HAVE practiced flushes at this depth.. doing 1 or 2 second flushes.. then waiting for the cells to catch up.. there is no need to keep flushing until the cells display what you anticipate if done correctly, if you wait then you could waste alot of gas.. Typical cells are 6 second full scale so it more like 2 or 3 seconds for a correct reading..

by crushing the breathing bags on a OTS system you have very little gas in the loop.. for all practical reasons just the hoses and cannister (your lungs you vent out the loop)..

If I keep hearing injections at 1.3 flushing with a mix that brings me to 1.2 and it displays 1.2 then I know I can trust my cells AT 1.2, but if that flush only gets me to 1.1 or less then I know the cells are not linear.. If you target a mix thats your calibration point you SHOULD expect it should be OK around there,, It could be off below or above this but at the cal point it should be close, so I want to test with a gas above this point..

And yes I have Had a solenoid that failed to close.. I was at 115m and my po2 hit almost 3 (it could have been higher but I never test my cells out that far) in the few seconds it took me to do a shut down.., I had it down to 1.3 in no time.. It did not take alot of effort.. crushed my bags, breathed out the loop and one big squirt of dil (it was 2 or 3 seconds at the most - In situations like this time perception goes out the window) and my po2 was only slightly higher than I wanted it (I probably didnt exhale as far as I could have), so I exhaled out of the loop the gas in my lungs and added a bit more dil..

There is no one correct way to do things.. I prefer to be able to verify my cells near where I am going to use them.. The quick dropping of the po2 to me is a non issue if you can do efficient loop flushes.. On a BM system it definately takes more gas than an OTS system where the diver can crush the bags manualy..

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

decoweenie

Yes Joe, in an ideal world, I agree that we should all be doing everything the most idealistic way...

We have a small boat that already carries a lot of divers and a lot of gears. There is barely room even to kit up. Most of the time I just throw my stages and scooter in the water first, and get don them on when I am in.

There is no space for everyone to bring a secondary set of tanks for that once in a lifetime cell error...

I am OK with that risk as I always calibrate, check for current-limiting at the beginning of the dive and don't push the cell life.

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decoweenie

Exactly!

As I mentioned in my first post, I usually penetrate at depth so I certainly do not want to switch to a high-PO2-high-PN2 gas, breathing like a race horse, narked as a drunken sailor and try to find myself out of the wreck before commencing ascend...

If you haven't done already, I recommend that you try to do a controlled bail-out exercise as you have mentioned with some safety divers and extra safety trimix stages (in case you can't go back to your unit) and see the effect.

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"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM

ScubaDadMiami

I like the idea of standard mixes where possible. It does not so much matter to me about which mixes so long as enough people are using them out there that we can switch bail out bottles during the dive without issue. Yes, it would be ideal to have custom mixes for every outing. However, I don't want to start dumping and remixing for every dive. So, I get somewhat practical about the situation, working within what I deem to be acceptable exposure ranges.

I want a dil flush to bring me down to 1.0 (which is where I almost always fly my unit--unless exposure requires it to be lower), and I am okay with bail out being somewhat hotter but within reason. (If in overhead, likely 1.0-1.2 max; if open water, 1.2-1.4 if not extended deco.)

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Howard Packer
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Skipbreather

Perhaps the safest way to try this, if a guy dives w/ BOV, would be to do a test dive w/ BOV temporarily connected to air. At depth give it a try w/ safety divers standing by to twist BOV back once you get realllllly stooooooopid...

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Andy Del

Getting back to standardised bailout mixes... it makes sense, if only because there is a ball park area where most (not all admittedly) would feel gasses x, y and z will do the job and get you home in one piece, having had to max bailout.

for me, this is:

to 50m
a - air diliuent, 40% intermediate gas, 100%
b - 15/55 diluent, 40% intermediate gas, 100%

to 80m

15/55 diluent (+ off-board cylinder), 40% intermediate gas, 100%

past 80m...

Well, I don't get to dive these depths that much. Last time it was a team bailout plan along the lines of:

120m dive

10/70 diluent, first bailout then to
15/55
21/35
50%
100%

Strangely enough, 21/35 and 15/55 is locally available premixed, and there isn't much difference between 40% and 50%. From what I have observed, most other divers around these here parts do similar up to 80m. (Did I say 'these here parts'? It is due to old dubbaya bering in town? )

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gathan

I played around for a while and eventually ended up settling on the following mixes:

18/45
35/25
EAN70

I usually run a SP of 1.0 on the bottom and bump it up to 1.2 at the first stop and raise it further for the longer shallow stops. If I bailout during the dive, the deco requirements are just about the same as if I was still on the loop with deco at 1.2 - makes it easy.

18/45 is plumbed into my BOV and I'm happy to use it down to about 90m ish, or so if not in an overhead. I now also have a second stage plumbed into my inboard O2 which I could use for a few minutes to do a "clean up" once the deco on EAN 70 is complete.

Andre

jradomski

for me its not just the cell, but having a better bailout gas for the depth.. If you don't have the option then the hottest mix that would meet my requirements for all the possible depths would be my choice..

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.