Gas planning for diving in mixed company?

[PfcAJ]

And the entire team did not fill at the same place???? On OC, I had 3 different tanks often with 2-3 different fills. I am not sure the team is any safer on bad gas here. It is possible everyone is in trouble. So how often have you dumped all of your CCR/BOs or Backgas/Decos because of bad gas? But now we are talking way outside standard deviation of risk....

Now lets get back to reality - So how many failures do you plan for. On OC, I did 2 critical failures on my breathing system and still surface. If a diver has more than 1 critical failure, I suspect they are the problem. Maintenance, Planning, Execution - etc.

The reality of the statement I made is - I do not plan on or expect to give gas to any technical diver. If they need it, they have made an inexcusable error in their dive philosophy. I have given gas to divers in deco to get them up, when they were not even my team. Go figure - have you.... Would you dive with them again, considering your life may be put at serious risk?

In my experience rarely does everyone get fills at the same place. Furthermore, bad gas starts at some point. That may or may not be you even if everyone gets gas at the same place. Eliminating the option in planning and preparation isn't doing you any favors should things go sideways.

Lamar English wrote a very interesting essay about his experience with bad gas. I suggest everyone read it.

The Deco Stop

 

[LiteHedded]

Bad gas does not happen at the end of a tank (typically) so if it was my back gas, dive terminated early and minimal deco. My planning has always allowed for removal of 1 or 2 of my deco tanks depending on what I was doing. So if both were contaminated, deco on back gas (part of my planning). Swap regs if needed or able. So unless all of my gas was contaminated and I even understood that is was (as my buddy's would also probably be), I would still have gas to get up.

The philosophy was taught to me by a very well known and respected wreck diver. Proper planning on the surface will negate most potential issues such as gas. It is always possible that you are not meant to finish (survive) a dive due to gas but then things have gone very south. I am thinking of the experienced divers in EN in this case. Notice I said that I would never plan on using someone gas. I also have allowed for failure of 1 to 2 pieces of equipment in planning. So yes, there is no reason for any technical diver to run out of gas. If you do, what did you do wrong.... and I would seriously reconsider my level of diving. I doubt many people can tell me of an incident where planning and execution was not the main issue, or something very odd like getting lost, stuck or taking your gear off....

I am not talking about expedition level diving here. This is technical level 'fun' diving. I am also not talking long distance penetration in caves although I am sure the same philosophy applies there. If you often need to borrow gas, you will have no buddies eventually.

yea I figured that

 

[KevinNM]

In my experience rarely does everyone get fills at the same place. Furthermore, bad gas starts at some point. That may or may not be you even if everyone gets gas at the same place. Eliminating the option in planning and preparation isn't doing you any favors should things go sideways.

Lamar English wrote a very interesting essay about his experience with bad gas. I suggest everyone read it.

The Deco Stop

It's too secret for me to see.

Is this the same essay he has on CDF?

 

[stuartv]

We are going there next month for the Oriskany. Our group is some TEC but mostly rec. we are told that they launch the TEC divers after the rec divers enter the water since we can only do one dive.

What boat are you using?

We're going out on the H2OBelow. The boat will be mostly sport divers and we only get to do 1 tech dive.

At this point, it has actually occurred to me that the boat may not allow us to bring more than 1 deco cylinder each. I have emailed the captain. If they won't let my buddy bring 2 cylinders (plus his CCR) and me 2 plus my doubles, then I am back to Square 0 for planning.

What extra training do you need that you already haven't had- you have a long list of certs and i would have thought you have enough bases covered to carry and extra bottle?/QUOTE]

My training thus far has only been for carrying 1 deco gas. My tech instructor that I have been training with teaches 1 deco gas during AN/DP/Helitrox and then 2 during Trimix. So, I have no training for carrying 2 deco gases. Do I think I could do it safely? Yes. I have read the course materials and I understand the process. Have I ever actually done it? No. And I'm not going to attempt to do it for the first time when diving the Oriskany.


Thank you all for the input. My buddy and I have traded a couple of emails about it today as well and I have new thoughts based on all the input.

One, it is now clear to me that CCR divers in general and my buddy specifically do not dive with any kind of plan that involves them giving their BO gas to anyone else. In my buddy's case, he's happy to carry bigger cylinders and extra gas for me to use, but he would not carry so little that my need of it would leave him with not enough for himself.

If I were to plan for myself to use 2 deco gases, and given that I need redundancy, I would have to either carry 4 actual cylinders, or my buddy would have to be carrying my redundant gas. Or I could carry 2 cylinders of deco gas that were each big enough that I could deco out on either one, if I lost one. None of that really works for me.

So, my current thinking is to go with a plan of carrying 2 deco cylinders myself, but both with the same gas in them and each one big enough to hold all the gas I need. I would only use one. The other would be my redundant supply.

Similarly, I would plan my rock bottom based on 2 divers. If I lose 1 cylinder of back gas, the other will still have enough gas in it to get me to my gas switch. That is, presuming suitably conservative rock bottom planning (i.e. recognize that losing 1 cylinder means I will lose some amount of gas from the other cylinder before I can get it isolated). The possibility of completely smashing my manifold and losing all my back gas does exist. That seems so unlikely that I think my buddy will be okay with agreeing that, in that case, he would donate me his bottom gas BO cylinder, to get me to my gas switch.

I feel like carrying 2 deco bottles of (probably) EAN80 is something I can handle without difficulty. There would be no risk of changing to the wrong gas, as there would be with carrying 2 different deco gases. Only the ever-present risk of doing a gas switch at the wrong depth.

And, as with "normal" diving where my buddy is on OC, as long as I don't have any failures, I will have enough bottom gas to donate and get us both out and I will have enough deco gas to give him a cylinder and still have one for myself.

Anybody see any problem I'm missing with this approach?

 

[Doby45]

It is always good to start with the boat rules first. As stated earlier the boat may also offer to hang regs at 20' for ya, I don't know. I am pretty sure @Wookie did that on the Spree during tech charters. This does not rule out you needing your own deco gas but is a good fall back if deco goes pear shaped.

 

[lermontov]

@stuartv

My tech instructor that I have been training with teaches 1 deco gas during AN/DP/Helitrox and then 2 during Trimix.

whats his reasoning behind that TDI Ex -range requires 2 deco gasses and its not trimix

So, I have no training for carrying 2 deco gases. Do I think I could do it safely? Yes. I have read the course materials and I understand the process. Have I ever actually done it? No. And I'm not going to attempt to do it for the first time when diving the Oriskany.

do you have time to practice ?

One, it is now clear to me that CCR divers in general and my buddy specifically do not dive with any kind of plan that involves them giving their BO gas to anyone else. In my buddy's case, he's happy to carry bigger cylinders and extra gas for me to use, but he would not carry so little that my need of it would leave him with not enough for himself.

I find myself checking their (CCR) gas plan as much for my peace of mind as much as anything


So, my current thinking is to go with a plan of carrying 2 deco cylinders myself, but both with the same gas in them and each one big enough to hold all the gas I need. I would only use one. The other would be my redundant supply.

Similarly, I would plan my rock bottom based on 2 divers. If I lose 1 cylinder of back gas, the other will still have enough gas in it to get me to my gas switch. That is, presuming suitably conservative rock bottom planning (i.e. recognize that losing 1 cylinder means I will lose some amount of gas from the other cylinder before I can get it isolated). The possibility of completely smashing my manifold and losing all my back gas does exist. That seems so unlikely that I think my buddy will be okay with agreeing that, in that case, he would donate me his bottom gas BO cylinder, to get me to my gas switch.

I feel like carrying 2 deco bottles of (probably) EAN80 is something I can handle without difficulty. There would be no risk of changing to the wrong gas, as there would be with carrying 2 different deco gases. Only the ever-present risk of doing a gas switch at the wrong depth.

And, as with "normal" diving where my buddy is on OC, as long as I don't have any failures, I will have enough bottom gas to donate and get us both out and I will have enough deco gas to give him a cylinder and still have one for myself.

Anybody see any problem I'm missing with this approach?

YOUve communicated with your buddy and he understands your position so a long as he takes equal responsibly as far as gas planning/sharing then you've done what you can- my preference is to take 50% mix to give me a deeper MOD and thus bigger overlap in terms of what depth I can use it compared to the Max depth if i had issues

 

[kensuf]

There are more reasons to bring 1.5-2x the amount of deco gas than you need for yourself than "my buddy needs deco gas."

Here's a couple to get you started.

1. Problem resulting in overshooting bottom time (increasing deco)
2. Debris in second stage causing free-flow
3. Working harder in deco than planned, causing higher RMV than used for calculations
4. Diver not part of your team in need of deco gas

 

[stuartv]

There are more reasons to bring 1.5-2x the amount of deco gas than you need for yourself than "my buddy needs deco gas."

Here's a couple to get you started.

1. Problem resulting in overshooting bottom time (increasing deco)
2. Debris in second stage causing free-flow
3. Working harder in deco than planned, causing higher RMV than used for calculations
4. Diver not part of your team in need of deco gas

Factoring those kinds of things in is part of calculating how much I need for me, which is not the subject of this thread.

 

[TrimixToo]

And the entire team did not fill at the same place????

In this area, it is more likely than not that the members of the team got fills in different places.

 

[doctormike]

With your bud being on CCR, I would plan the dive as solo.

I have considered that approach. The result is MUCH less bottom time.

I'm only mod 1 on CCR, so I'm not really qualified to discuss staged deco on a rebreather. But when I was doing OC tech diving, I never included another diver's gas in my plans. I planned bottom time assuming that I would need to get myself to the surface using what I was carrying, and that included lost gas scenarios. Maybe that's indicative of local (NYC area) diving culture, maybe things are different in caves or other ocean locations.

I don't know what sort of depths you are planning, or how much deco you are comfortable racking up, but I'm sure that you can plan for a nice tech dive without depending on your buddy's gas to make it acceptable.