Deco dive with divers on different back gas

[sunny_diver]

Diver A has air. Diver B has EAN32. Both have 50% for deco.

The dive is 100 ft for 30 minutes. Let's say using air would require 16 minutes of deco and EAN32 requires 8 minutes.

The EAN32 diver agrees to put their computer in air mode or use air tables. Both divers follow the same deco schedule and do 16 minutes of deco.

If a gas share is required, they still assume the back gas is air.

Any downsides?

 

[rjack321]

Any downsides?

Yes you posted in the wrong forum. Consistent team gas choices are a "before you leave the dock" requirement.

Also air is not used, especially for a 100ft deco dive.

 

[sunny_diver]

Yes you posted in the wrong forum. Consistent team gas choices are a "before you leave the dock" requirement.

I debated on posting here or the parent Technical Diving forum. Maybe it's a topic for a different post, but it's not obvious to me if DIR only means what George Irvine defined or if it's a more broadly used term now. Sounds like it's the former.

Also air is not used, especially for a 100ft deco dive.

TDI AN/DP divers use air to that depth and deeper. Maybe TDI isn't DIR though? Same point as above.

 

[boulderjohn]

You will get answers to your question if you post in a different forum.

 

[boulderjohn]

TDI AN/DP divers use air to that depth and deeper. Maybe TDI isn't DIR though? Same point as above.

As an agency, TDI isn't DIR at all. I do know some TDI instructors who are also DIR, but that is an individual choice. The founder of TDI, Bret Gilliam, was very much opposed to George Irvine and the DIR philosophy in general. I talked with him about it years later, and he still went into a rage. When I took TDI training years ago, I identified very clear anti-DIR comments in the materials. My TDI instructor knew nothing about DIR, so I had to explain to him what the comments meant. (Those materials are long gone.)

 

[Badger7]

Any downsides?

The downsides seems pretty cut & dry by "DIR" or really any other diving standards/theory:
1) Diver B is stuck doing 8 extra minutes of deco because his teammate showed up with the wrong gas for the dive plan
2) Diver A is taking on additional nitrogen exposure for absolutely no reason or benefit because he showed up for the wrong gas for the dive. If he was able to get his deco bottle filled up with 50%, he could have gotten his back gas filled with 32% which would be far more appropriate for a 100' dive than 21%.
3) Trusting anything your computer tells you when you have it set to the wrong gas mix is never a good idea for any reason or any scenario, that should be self-evident.

 

[sunny_diver]

Post moved to Technical Diving.

 

[grantmac]

I have done deco dives with one diver on air and another on trimix because they know that they have a history of narcosis. That made sense on that particular dive.

Mixing air and EAN doesn't make sense though.

 

[arkstorm]

I have done deco dives with one diver on air and another on trimix because they know that they have a history of narcosis. That made sense on that particular dive.

Mixing air and EAN doesn't make sense though.

Why? How is EAN different then trimix in that scenario?

 

[grantmac]

Why? How is EAN different then trimix in that scenario?

The Trimix diver accrued similar deco obligation to the air diver based on the plan (35m/30min).