stage tanks and OOA procedure

[nadwidny]

Do you really bring a safety diver along on any dive that requires decompression?

I don't but people are looking for the DIR answer.

Funny nobody has mentioned swapping regs underwater to solve the problem, which is another DIR answer.

 

[nadwidny]

My point to Brian Nadwidny was that I can't imagine requiring safety divers for most dives above say, 200' or so where gas related issues are very manageable. Obviously it becomes very difficult to carry all your own gas along with contingency gas on dives exceeding 250' or so and support divers become a necessity, especially in ocean diving, simply to offload gear from you and monitor you during the lengthy decompressions.

I was also curious at what level he brings support divers along.

For our Halifax expedition this past summer we had one for dives beyond 200 (thanks JeffG, safety diver extraordinaire). All other dives, even the 140/150 range were done sans the SD but with 2 deco gasses which made reg switching a possibility. For the most part if we are doing any deco at all we do it with 2 deco cylinders; partly for reg redundancy, partly for other reasons. Switching may mean the reg needs a service right afterwards which is a PITA but dealing UW with a diver who has lost one of his deco gasses is much more of a pain.

 

[Soggy]

For our Halifax expedition this past summer we had one for dives beyond 200 (thanks JeffG, safety diver extraordinaire). All other dives, even the 140/150 range were done sans the SD but with 2 deco gasses which made reg switching a possibility. For the most part if we are doing any deco at all we do it with 2 deco cylinders; partly for reg redundancy, partly for other reasons. Switching may mean the reg needs a service right afterwards which is a PITA but dealing UW with a diver who has lost one of his deco gasses is much more of a pain.

We are beginning to do the same, except for deco dives within 'recreational' depths where backgas deco is easy.

 

[limeyx]

I don't but people are looking for the DIR answer.

Funny nobody has mentioned swapping regs underwater to solve the problem, which is another DIR answer.

yeah, If only I had mentioned it in post #29

 

[nadwidny]

yeah, If only I had mentioned it in post #29

So you did. Sorry about that Chief.

 

[limeyx]

So you did. Sorry about that Chief.

heh, no worries. Fortunately never had to do it so far.

 

[nadwidny]

heh, no worries. Fortunately never had to do it so far.

Had a friend that did it once in freshwater in a non-critical situation just to see if it worked; it did.

I almost had to do it once for real in saltwater but luckily for me I got things sorted out just before I made the switch. That was the end of my "second stage should be hand-tight" experiment. A few weeks later JJ posted on Quest that "second stage hand-tight" was no longer recommended.

 

[MXGratefulDiver]

First, you don't get into the water needing 75% of your deco gas. You reserve 1/3rd of your deco gas for emergencies, thus never plan on using more than 27 cft in an al40 and 50ish cft in an al80. That way, you can have enough gas to do all your deco x1.5 if a teammate loses his.

The team stays together. If you have a teammate that has lost deco gas, you would extend the time by 1.5x (2 minutes becomes 3 minutes, 3 minutes becomes 5 minutes, 4 minutes becomes 6 mins, etc). You would then do half of the original time (or 1/3rd of the extended time) on your deco gas, then pass the reg off to your buddy where they would do an equal amount of time on the deco gas. 2/3rds of the total extended time will end up being on back gas. That way, everyone has enough (or close to enough) gas and the team can stay together. The most important part, the deep stuff, is done, and if you run out, your can double your remaining stops.

That exactly describes what I was taught in my NAUI Advanced Nitrox class as well ...

... Bob (Grateful Diver)

 

[ianr33]

I am assuming that increasing the deco by a factor of 1.5 is only applicable to the loss of a 50% deco bottle? (and comes from the fact that 50% halves deco times compared to a typical backgas?)

Presumably if you lost an O2 bottle then 2 divers could alternate backgas and the one bottle of O2 if the deco time was doubled? (deco on O2 is about 1/3 deco on backgas)

 

[Soggy]

Presumably if you lost an O2 bottle then 2 divers could alternate backgas and the one bottle of O2 if the deco time was doubled? (deco on O2 is about 1/3 deco on backgas)

For the purposes of battlefield calculation, I would still use 1.5x. In open water, presumably you'd have a 50% bottle anyhow if you are carrying 100% and you could switch regs, or if that isn't possible, do as much deco as possible on 50% before sharing.