Gas planning for diving in mixed company?

[TrimixToo]

I think doctormike's approach is common for much of the Northeast.

 

[Jack Hammer]

In tech diving you need to determine what your acceptable level of risk is otherwise you can very quickly and quite easily plan yourself out of a dive.

 

[Doby45]

In tech diving you need to determine what your acceptable level of risk is otherwise you can very quickly and quite easily plan yourself out of a dive.

Spoken for truth and what I tried to convey earlier in the thread. I mean you can get to the point that you are planning for the boat to sink and sharks to be in the area and a meteor strike near by that will end the earth. Meh, stay home at that point.

 

[doctormike]

Spoken for truth and what I tried to convey earlier in the thread. I mean you can get to the point that you are planning for the boat to sink and sharks to be in the area and a meteor strike near by that will end the earth. Meh, stay home at that point.

Right, but I think that Stuart's question was: do the normal rules of only planning for one failure apply to mixed OC/CC teams, which is a good question. Especially coming from a non CCR diver, it's not alway apparent.

The reason that we generally don't plan for multiple failures is that if the chance of each one happening is a low percentage, then the chance of two of them happening is a low percentage squared (i.e. a REALLY low percentage). So I wouldn't plan a tech dive with enough gas to cover losing both my deco gas and my back gas, because soon you won't be able to dive at all if you have to carry enough for that.

To a non-CCR diver, however, it's not clear if the need to bail out for any one of a number of problems is much more likely than the need to, for example, run a lost-gas ascent on OC. So it's a reasonable question.

To be honest, I would NOT feel comfortable handing off my bailout to an OOG OC diver, just because the chances of him going OOG and me needing bailout on the same dive are small. I want my bailout no matter what (especially as a new CCR diver). I'm actually trying to work out my mixed team bailout regulator right now - necklace reg for me, second 2nd stage bungeed to tank with a shutoff valve to donate. And I'm carrying an AL80 bailout, so I'm definitely planning for reserving the option to bailout even if I need to donate gas in a non-deco situation.

 

[kensuf]

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

So if you're adding 2x more gas into your plan than your "rock bottom" amount to get to the surface, than you're already covering buddy gas.

Your CCR buddy needs to have enough bailout gas to get the two of you to the first deco stop, and enough deco gas to get the two of you to the surface. He also needs to be prepared to hand you a regulator.

Now, let's look at the real questions you asked:

Since my buddy will actually be on a CCR and will be carrying BO cylinders of bottom gas and deco gas that will be sufficient to get him safely from the furthest point in the dive to the surface in the event he has a CCR failure, my thinking is that I do not need to reserve any of the gas I'm carrying for him. But, I can plan to use his, if needed.

So, my rock bottom planning would be for 1 diver, instead of the usual 2. And I can plan that if I have any lost gas, I can use one of his BO cylinders.

As I said above, you need to adjust that and have enough gas for the two of you.

This thinking is all based on the usual approach of only planning for 1 failure. But, I don't know if that's valid when you're talking about a CCR diver. Is it?

In answer to the question of failure modes on rebreathers, CCR's can be robust machines. They can also be fickle beyotches. My limited experience (about 350 hours divided between two units) tells me they're pretty reliable if well maintained, but I've seen weird stuff happen on poorly maintained units.

My general rule when diving my machine is that I have enough OC bailout to get myself and my buddy to the surface. In other words, I carry the same amount of deco gas as an OC buddy, and I carry at least 2x times the bottom mix we need to get to the surface. In essence, I am planning for two failures, but in the case of a dive like you're doing, in practicality it means I am only bringing two AL80 bailout bottles (one of deco mix, one of bottom gas).

Is it acceptable to plan that if I lost my deco gas, I can just take the deco gas cylinder my CCR buddy is carrying? Is it acceptable to plan that if I somehow lose all my back gas, I can take the bottom gas BO cylinder my buddy is carrying?

In answer to the "is it acceptable to plan that if I somehow lose all my back gas, I can take my buddy's?" -- really, you need to have a conversation with your buddy before you ever get to the boat. He may think it's acceptable, but he may also think it isn't. Some CCR divers are fiercely independent, and if you show up to the boat anticipating that he's ready to give you gas, and you find out he isn't, well.

Or does diving with a CCR have elevated risk such that a CCR diver would/should never dive with a plan that includes him having to donate one of his BO cylinders to someone else?

Diving on a CCR entails additional risk beyond OC. However, that doesn't necessarily mean that your CCR buddy is unwilling to donate his BO cylinder to you. IMHO, if we're diving together and I'm on my machine, and you need gas, you're getting a regulator. It's that simple. But that's me.

I will discuss all this with my buddy, of course. But, I want other opinions just to reassure me that if he says this is an acceptable plan, there is no part of his acceptance that is based on a feeling of pressure from me or a willingness to compromise on safety to get decent bottom time when he's handicapped by diving with an OC diver. I don't believe he would do any of that. I'm just paranoid and like to get other perspectives on the relative safety of what I'm proposing.

Talk to him. Tell him you want him to be comfortable with the plan. And you need to understand what his expectations from you and your expectations of him are. Explain to him that you've never dove with a CCR diver, and you're not sure what to do. Heck, ask him to review some of the safety features on his unit; if he has a HUD or a Bail Out Valve, have him explain those to you so you can also monitor his gas and know how to get him on OC.

Finally, enjoy the big O. It's supposed to be a great dive.

 

[Michael Guerrero]

My thoughts are that if you're not trained to dive mixed teams you're violating your training, and if you're not trained to conduct solo tech dives you're violating your training.

 

[Michael Guerrero]

it has actually occurred to me that the boat may not allow us to bring more than 1 deco cylinder each.

My dives on Capt Douglas' boat were with doubles, two deco cylinders, and a scooter. You guys should be fine.

 

[lermontov]

My thoughts are that if you're not trained to dive mixed teams you're violating your training, and if you're not trained to conduct solo tech dives you're violating your training.

Theres a course for mixed teams?
what would it entail that couldn't be covered by basic gas planning

 

[KenGordon]

Stuart, if you are limited to one cylinder for either bailout or deco gas then your main problem is what to do if you have a deco gas failure. However that is the same problem the CCR diver has in the event of many failures leading to bailout.

Either you need to limit your dive to allow for backgas deco or rely on the CCR diver's bailout for deco. It can be richer than your backgas as he can run 1.6 ppo2 for bailout. Something like 30% might do.

Your CCR buddy is unlikely to be getting a bailout mix just for this dive though. He might be counting on being able to go back on the loop shallow or using YOUR deco gas after his deep bailout. In that case he might have bailout which is totally useless to you as a deco gas.

On CCR I would want two bailout cylinders for this dive. That is true for me once I get past OC backgas deco territory. Really diving CCR is like OC twinset but always requires an extra cylinder.

Another think to consider is to take two identical deco gases. That way your gas switching etc isn't so risky.

 

[Centrals]

1. Deco gas failure is part of the original training. I do not see any reason to bring a spare tank for that.
2. He is only entitled to one cylinder for either bailout or deco.