Disturbing 'advice' from DAN in Alert Diver

[knotical]

Found this in Lippmann and Mitchell's Deeper into Diving.

It is also possible, although currently unproven in humans, that the rapid delivery of bubbles to, and consequent overloading of, the pulmonary circulation may result in some bubbles passing directly into the arterial circulation.

(underlining mine)

That's from the 2005 edition. Is there anything more recent?
Is it possible that DCS cases attributed to bubble pumping might have happened anyway?
Is it possible that such DCS cases occurred because of some other mechanism?
Or is this something that we just don't know yet?

 

[Blackwood]

^ not sure what "the" current thinking is, by I have heard of bends cases from shallow dives attributed to this specifically (my wife's, for example).

I thought Geo Irvine specifically warned about this issue and referenced divers retreiving deco bottles getting bent. I always assumed the deco bottles were "shallow".

Do I misunderstand his admonishments or has the thinking changed in the DIR world?

He also warned against free diving following dives.

I think a more common application is going down to free an anchor chain or shotline, etc.. It's done without I'll effect quite often, but so is driving tired.

 

[rstofer]

I don't think the dive computer logging features really play into this argument one way or the other. Whether or not a computer counts a dive as one or two is probably thought of as a convenience feature more than something they spent any amount of time worrying about from a safety perspective.

Tom

Well, if the computer is happy, why don't I just grab another tank and head back down to 100' or so? As far as the computer is concerned, this isn't a problem. It's just a continuation of the previous dive.

So, what's the difference between a recompression dive and an interrupted dive? As long as the NDLs aren't violated, everything should be fine.

But, there's anecdotal evidence that all won't be fine. Or, that's the gist of this thread. Didn't the diver just dive back down to 50'? That part where he ran out of air was unfortunate but if he didn't violate the NDLs, he really didn't need to make a final safety stop. Or, did he violate the NDLs.

Is the problem recompression or a simple violation of the NDLs?

Richard

 

[Blackwood]

Is the problem recompression or a simple violation of the NDLs?
Richard

NDL, schmen DL

(sorry, that's the best I can come up with).

The problem I'm trying to discuss is short re-compression.

 

[lowviz]

... short re-compression.

I assume the issue revolves around bubbles that are rapidly re-compressed so that they pass the lungs but are not in equilibrium with the blood gas tensions. I also assume that the problem is decompression before equilibrium is re-attained. Or is it just the point that the microbubbles make it through to the arterial side?

 

[rstofer]

The problem I'm trying to discuss is short re-compression.

I understand that. What I don't understand is the difference between short re-compression and an interrupted dive. Apparently the computer doesn't care if you surface to change tanks and dive back in.

A computer will probably be quite happy with a 100' dive followed by surfacing to change tanks and a continued dive to some depth, perhaps even including 100' At least the GEO doesn't seem too concerned about it, other than the usual nitrogen loading. There is certainly no admonition to stay on the surface once you get there.

There is only a requirement to change tanks in less than 10 minutes.

I have no problem with the idea of staying on the surface once you get there.

Richard

 

[Blackwood]

I understand that. What I don't understand is the difference between short re-compression and an interrupted dive. Apparently the computer doesn't care if you surface to change tanks and dive back in.

Nor do I, so long as you remain underwater sufficiently long.

I'm operating under the assumption that the Geo programming is trying to not punish you for surfacing by counting an extremely short surface interval into a repet dive, but that it doesn't expect that repet dive to be on the order of a few minutes.

In any case, you can't program for every situation.

 

[Blackwood]

I assume the issue revolves around bubbles that are rapidly re-compressed so that they pass the lungs but are not in equilibrium with the blood gas tensions. I also assume that the problem is decompression before equilibrium is re-attained.

Indeed. That's what I meant by "short" re compression. Shrinking the bubbles and thus allowing them access to places they aren't meant to be, and then growing them (by ascending) shortly after. That was the first plausible explanation to my wife's type II hit (diagnosed and treated by a hyperbaric MD) following a couple of 32% dives with a max depth of 60' (avg in the 40s) for about 50 minutes each, the second of which she popped up towards the end and re-descended for the swim back to the boat.

 

[lowviz]

I'll be doing my first decompression dives this year. However, my real interest in this thread stems from the possibility that one can crap-up a no-deco dive sufficiently that you end up in exactly this situation. -I've done my share...

 

[lowviz]

That was the first plausible explanation to my wife's type II hit (diagnosed and treated by a hyperbaric MD) following a couple of 32% dives with a max depth of 60' (avg in the 40s) for about 50 minutes each, the second of which she popped up towards the end and re-descended for the swim back to the boat.

First, I hope your wife escaped without issues. Secondly, it is a real eye-opener that a single bounce like that generated a type II hit. Instructors doing multiple ESA's are indeed at risk.