Decompression in very cold water

[rjack321]

This really is the one failure that we can't do a hell of a lot about. We can dive purpose-made undergarments, and cinch up gauges, but in my experience with flooded suits I still get cold, and fast.

I see this as the major limitation in cold water deco diving. At the end of the day I think it's wise to have a plan for cutting time. Coupling that with trying to figure out what you think you will be able to get away with in terms of time in the water with a flooded suit. This would give a picture of what to plan for in terms of max deco obligation.

For the most part I agree with rjack123's numbers. I might stay a little longer, but not much.

Me too, purpose made or not big leaks are really cold, really fast in sub-60F waters. 400gm Thinsulate or the Weezle mateials can handle 60F leaks "ok" but even a torn dryglove in 40F water is alot colder than I'd want to deal with for hours.

If I'm cutting deco I'd do all the deeper gases (EAN50) and as much O2 time as I can stand. Surface and do at least as much O2 time as possible in a warm environment with warmer clothes and warm water bottles in my armpits etc.

 

[rx7diver]

... [T]he whole concept of very cold water diving and decompression diving got me thinking ... . What would someone do if there was a significant deco obligation and a drysuit failure ... .

OP, thinking about things like this is what originally launched me down the slippery slope of tech diving. When I moved near the Great Lakes in the early '90's and started thinking about diving some of the deeper (though not extremely deep) shipwrecks there, I decided I absolutely needed a drysuit that was difficult/nearly impossible to hole. So I purchased a custom DUI CF200SP (crushed neoprene) with neoprene fold-under neck- and wrist seals, and thinsulate undergarments. Neoprene seals are extremely durable and less likely to fail (though a bit less comfortable, perhaps) than silicone seals, and thinsulate undergarments will keep one warm(er) even if flooded.

When I started thinking about doing deco dives there--you know, so that I could stay a bit longer at those deeper depths--I became aware of something called "accelerated Oxygen decompression" (where a diver, I was told, would switch to Oxygen at his/her 20 ffw stop, and subsequently shave 33% off his/her 20- and 10 ffw stop deco times). Anything that would get me out of that frigid water sooner was something I definitely wanted to learn more about!

Then came the formal tech courses, which taught me about choosing a bottom gas to minimize inert gas loading (which minimizes deco obligation), and Nitrox "wash-out" gases that could be used before one ascended to his 20 ft stop (which reduces even further the remaining inert gas left for the Oxygen to eliminate).

So, my personal interest in tech diving really had nothing to do originally with descending ever deeper and staying ever longer. It really had to do more with being able to do not-so-deep, relatively short bottom-time deco dives in (to me) very cold water. I wanted to be able to do a 20-25 minute dive in the 150-175 ffw range, but with a reasonably short run time (i.e., I wanted to spend the minimum amount of time decoing in those freezing Great Lakes!).

Anyway, maybe the answer to your question might be, if practical, avoid diving a plan that would give you a significant deco obligation when diving in extremely cold water.

(Still, when I hear/read about some of the amazing dives people have made to the truly deep Great Lakes shipwrecks, ...)

Dive Safely,

Ronald