Deco dive with divers on different back gas

[sunny_diver]

The EAN32 diver agrees to put their computer in air mode or use air tables.

Why does the EANx diver agree to do this?

So that during the dive the EAN32 diver can see the expected deco schedule. I see better ideas from others in this thread though.

What prevented the air diver from drawing a better gas?

I created an example to keep the post simple, but imagine this. Divers A and C planned to dive on air. A separate team at the same dive site, divers B and D, planned to dive EAN32. Diver D discovers an unfixable gear problem while getting kitted up. Diver B asks if they can join the air divers A and C, on their dive.

 

[sunny_diver]

And you all keep going on about janky work arounds instead of just saying "nah not diving today". That's what both should do about it instead of asking strangers on the internet. It's a sloppy slippery slope which they already started with this purported 'plan'

@rjack321 can you think of how to be friendlier on Scubaboard? In general, your posts are unnecessarily confrontational and often not helpful. I invite you to imagine an Internet where people talk to each other online just as they would in real life.

 

[Boarderguy]

@rjack321 can you think of how to be friendlier on Scubaboard? In general, your posts are unnecessarily confrontational and often not helpful. I invite you to imagine an Internet where people talk to each other online just as they would in real life.

That's part of the DIR/GUE mindset and dogma that is oh so off putting. Below 100 requires trimix and everything is black. Color and personality are only acceptable on your surface Halcyon gear such as your changing mat.

 

[DiveLikeAMuppet]

The downside would be that one of the divers brought the wrong gas, so the other diver will have a very short dive. The air diver would be cutting down the “activity” length by half, I wouldn’t dive with someone like that again unless we were good friends.

With a square profile, at 30 meters using 32% nitrox backgas and a 50% deco stage you can nicely max out your bottom time to about 45-50 minutes. Diver on air is a muppet who will need to cut the dive short, probably at 30ish minutes. This assumes taking into account a lost deco gas scenario which will be the main limit of the air diver (yeah teammate might be around with their 50% but try relaying on that in 2 meter viz).

What I would do is wave a good bye to the air diver and stay longer.

 

[NothingClever]

That's part of the DIR/GUE mindset and dogma that is oh so off putting. Below 100 requires trimix and everything is black.

It’s not GUE dogma but hyperbaric research and a recommendation from DAN.

Performance Under Pressure

Gas density is one of the unknown mechanisms on the forefront of hyperbaric research.

dan.org

Helium appears to be the immediate solution for divers who are concerned about WOB and correlated medical issues (immersion pulmonary edema, CO2 retention, etc.) and for technical divers who are doing even normal dives to moderate depths.

I encourage folks to read the whole article.

 

[NothingClever]

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.

DIR is a legacy term and George Irvine hasn’t been heard from in decades.

ScubaBoard perpetuates both to the detriment of many.

 

[LFMarm]

Once you are doing a stop together, you ascend to the next stop when both divers are ready for it. Again, there is no harm to the diver who is staying a little longer.

I fully agree with the recommendations but there may be situations where there is some harm. If the divers have mismatched GFs and one of them has a lower GF low / higher GF high (e.g., 30/95), the other diver may suffer from a more inefficient decompression compared to his programmed one (e.g., 60/72).

Diving similar and agreed before hand GFs is another practice I prefer to avoid disagreeing underwater during deco.

 

[rjack321]

Boy, I just don't see it as that big of a deal. If I had a buddy who had doubles filled with air and I had doubles filled with 32%, I'd do the dive. It's a pretty simple basic deco dive. I don't see why people are getting their panties in a wad over this.

So when 2 divers up with 18/45 and 21/25 for a 150 dive do they just buddy up casually too? Where does this slippery slope end? Part of making a deco dive <PLAN> is ensuring you're both doing the same dive and here we have 2 divers deviating from one of the basics before they even get to matching rock bottoms, potentially with dissimilar tanks, or mismatched stressed SACs, OOA plans, or anything else. It's a same ocean dive, just go solo if not having a common plan is that trivial.

 

[boulderjohn]

So when 2 divers up with 18/45 and 21/25 for a 150 dive do they just buddy up casually too? Where does this slippery slope end? Part of making a deco dive <PLAN> is ensuring you're both doing the same dive and here we have 2 divers deviating from one of the basics before they even get to matching rock bottoms, potentially with dissimilar tanks, or mismatched stressed SACs, OOA plans, or anything else. It's a same ocean dive, just go solo if not having a common plan is that trivial.

So we go from a pretty simple, barely-into-deco dive to full on hypoxic with all sorts of other issues. That is just an absurdity.

The "slippery slope" argument is a fallacy, and you are showing why. The fact that something makes sense in one situation does not mean it will make sense in another. That is why we have to use our minds and not follow dogma that might make sense in one case and not in another. Once you have become part of the dogma, though, it can be hard to see that. It took me a long time to clear that junk from my brain.

 

[boulderjohn]

I fully agree with the recommendations but there may be situations where there is some harm. If the divers have mismatched GFs and one of them has a lower GF low / higher GF high (e.g., 30/95), the other diver may suffer from a more inefficient decompression compared to his programmed one (e.g., 60/72).

Diving similar and agreed before hand GFs is another practice I prefer to avoid disagreeing underwater during deco.

Why do they have mismatched GFs? Does having different gases require you to use different GFs?

In the deco dives I have done over the years, we try our best to get the same gas mixes, but when you are blending gases in a motel parking lot, it can be tough. We always discuss GFs ahead of time to make sure we are on the same page. No one has ever told us we are not allowed to do that.