Deep Bailout Gas Choice for ~70M / 230FT

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Peter L

Active Member
Due to my deep bailout tank doing some wierness on it's calibrations and some suspected heliums make a run for it past the valve since it's last fill 2 years ago I am having to have it serviced and re-filled.

What would people use as a bail out gas at that depth and why?

Note, I am not quall'd to this depth but will be shortly, it seems to be a bit of an issue finding a bail out gas that covers 60-75M cleanly without hitting an ICD warning on bailout somewhere in the steps.

PL
 
I've been using 15/50 for a standard dil and deep bail gas for some time
It does give you a little more deco than a less hot mix; but I have noticed that backing off to say an 18/30 doesn't leave me as clear headed so I'm happy with a few minutes more on the line
 
SoggyBottoms said:
I've been using 15/50 for a standard dil and deep bail gas for some time
It does give you a little more deco than a less hot mix; but I have noticed that backing off to say an 18/30 doesn't leave me as clear headed so I'm happy with a few minutes more on the line
Click to expand...

15/50 is the choice that fits from an OC perspective but at 70M is a bit hot for both dil flushing and breathing viscosity at depth in a crisis bail out?
 
I'm in the same boat as you - thinking about the next step. I have been weighing up using 18/45 for deep bailout, then something like 35/20 as an intermediate gas, followed by O2..
I realise it's an open circuit mindset, but it's just become an open circuit dive. I'd prefer a fair bit of helium in the deep mix in case I'm chuffing like a train after a co2 issue.
As far as I've managed to glean so far, at this level of diving it's only really a co2 hit or major flood that's going to force you off the loop.
 
steve6690 said:
I'm in the same boat as you - thinking about the next step. I have been weighing up using 18/45 for deep bailout, then something like 35/20 as an intermediate gas, followed by O2..
I realise it's an open circuit mindset, but it's just become an open circuit dive. I'd prefer a fair bit of helium in the deep mix in case I'm chuffing like a train after a co2 issue.
As far as I've managed to glean so far, at this level of diving it's only really a co2 hit or major flood that's going to force you off the loop.
Click to expand...

The mantra I have for better or worse been given is try and keep an END of less than 20M / 60FT and PPO2 of 1.1 for bail out and at 70M depth this becomes too lean for travel up to 50% and the ICD and worse yet you need a lot if it's a bail out for anger hence the intermediate bail out that would be in place of straight to 50%. I am also assuming that the first tank is scrap metal within 5 minutes so don't plan on it getting you to 21M....
 
Peter L said:
15/50 is the choice that fits from an OC perspective but at 70M is a bit hot for both dil flushing and breathing viscosity at depth in a crisis bail out?
Click to expand...

Just running some quick maths...
@70m the 15/50 dil flushes to 1.2, nice and easy to spot and a good way to check the cells (or 1.1 @63m)

and the density of the various gas mixes is:
Air @70m - 9.6Kg/m3
15/50 @ 70m - 5.55kg/m3
10/90 @ 70m - 2.28kg/m3 (that's about as 'thin' as it gets, air on the surface is 1.2047kg/m3)

but the runtime for bailing out on the 10/90 is 382min and you'd need 13,068L of it. The runtime for 15/55 is 169mins and you need 4,047L of deep bail so doable on team bailout (based on 70m for 30min and 50% and 100% on top of deep bail, on a quick and dirty play on iDeco) if you go richer on the helium, you do more deco.

(I'm assuming you meant density as that's related to WOB, as they are gases the true viscosity is around 1.8E-5 kg/m.s with helium being more viscous than air)


Regards,
B
 
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erikradstrom said:
I did that dive yesterday, had a 80cf 15/55 + 80cf 50/25 and a 40cf 100
Click to expand...

I like that better. Swapping at 35m to 35/25 leaves me a bit short on gas to get to 6m.
Anyway, my point was about trying an intermediate trimix gas instead of swapping from deep bailout onto 50%.
 
Peter L said:
:trophy:

Cracking.. that was kinda where my numbers were pointing to.
Click to expand...

I was just about to cook dinner when I wrote it but now I have little more time to explain why I have it like that.

The dives I do I plan not to use the gas SCR, I bail out, final. I bring enough gas to make it all the way.
if I would need it as diluent it´s fine, little high PO2 but in a situation I need to use my bailout as diluent I probably abort the dive or have in mind that it is little higher than normal.

The consumption up to 21m is not that high, the long stops usually comes after 21m and I think it´s better to have more gas in the next bottle instead of changing earlier.

50/25 I added a little helium to give the bottle little float. Some may find it better in case of ICD but personally I have it more to get the bottles floating.

100% is so I can use it as a backup if the solenoid/leaky valve or what else you have breaks or something else happens so I cant get the onboard O2.

Would be nice to read if any has any other solutions!
 
I use a completely different approach than most folks I know and put my deep dil/bailout offboard while always having a normoxic mix onboard that is part of my bailout calculations. Using my standard mixes (I tolerate a higher END than you) my gasses would be
80cf offboard 14/45
30cf onboard 28/20
80cf offboard 45%

Based on a 30 minute BT, the bailout scenario adds only 16 minutes, no ICD warning, and only 2 offboard tanks to carry. All gasses are available either through BOV or second stage, including the onboard tank.

My approach is clearly not for everyone, but it works for me.
 
kwinter said:
I use a completely different approach than most folks I know and put my deep dil/bailout offboard while always having a normoxic mix onboard that is part of my bailout calculations. Using my standard mixes (I tolerate a higher END than you) my gasses would be
80cf offboard 14/45
30cf onboard 28/20
80cf offboard 45%

Based on a 30 minute BT, the bailout scenario adds only 16 minutes, no ICD warning, and only 2 offboard tanks to carry. All gasses are available either through BOV or second stage, including the onboard tank.

My approach is clearly not for everyone, but it works for me.
Click to expand...

What CCR are you on and I am assuming you have a flow stop on your ADV?
I am interested in the idea of a travel gas inboard but have concerns around plumbing and boom scenarios...
 
Deep bailout has to cope with three major issues:

1: Narcosis under stress asnd possable C02 hit

2: Oxygen toxisity which is possably hightened by high C02 levels in the blood

3: It needs to be as low viscosity gas to reduce the effects of retained Co2 due to WOB issues = loads of low viscosity Helium


So for a 70m dive you dont want to be over 1.2PP02 so max 15% 02

I chose 15/65 for this dive

ATB

Mark
 
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Peter L said:
What CCR are you on and I am assuming you have a flow stop on your ADV?
I am interested in the idea of a travel gas inboard but have concerns around plumbing and boom scenarios...
Click to expand...

I dive an Optima. It comes standard with a flow stop on the ADV. I modified it with a manifold block on the dil side to feed ADV, MAV, wing, and BOV. So whatever gas is driving the RB is driving everything. I have a 3-way ball valve that feeds into the manifold block. One input is from the onboard tank and the other is a QD for offboard. All bailouts have matching QD and can be plugged into the ball valve. Using a combination octo/inflator gives OC access to the onboard tank as well.

Yes, Mark, it adds potential failure points. And yes, Mark, you have to be careful which gas is active from the ball valve. But I find the convenience worth the extra diligence. I always have a breathable gas connected to my BOV no matter what depth. My onboard tank is always normoxic. When I surface, I can disconnect all offboard tanks and hang them or hand them up while I still have a breathable gas connected in case of a problem.

As I said, its not for everyone.

Ken
 
Mark Chase said:
Deep bailout has to cope with three major issues:

1: Narcosis under stress asnd possable C02 hit

2: Oxygen toxisity which is possably hightened by high C02 levels in the blood

3: It needs to be as low viscosity gas to reduce the effects of retained Co2 due to WOB issues = loads of low viscosity Helium


So for a 70m dive you dont want to be over 1.2.3PP02 so max 15% 02

I chose 15/65 for this dive

ATB

Mark
Click to expand...

Thanks, this is where my thinking was starting from in concept. The question is how quick would you get off the deep mix, I am almost thinking that the first bottle should be gone pre-deco depths. What would be the next one you add to this?
 
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