Question Multiple Deco Dives in One Day Experience and Rules

[Winstone]

Hi Tech divers, so I have a question I know that in general the advice is that when conducting a decompression dive you should not do a 2nd dive on the same day, but I have been on multiple tec dives with a mix of technical and recreational divers on a boat and I am in the minority of the Tec divers who miss out on the 2nd dive. I have even seen tech divers conducting multiple decompression dives after 1hr surface interval and even 3 consecutive dives.

When I calculate using multi deco depending on the profile it looks like it’s technically possible so I am asking what other technical divers experience has been and any specific rules/ guidelines that you always adhere to.

Thank you and Happy Diving

 

[boulderjohn]

It depends upon how serious the first deco dive. I have frequently done more than one decompression dive in a day. There are lots of shallower depth decompression dives that can easily be repeated in a day. When teaching technical diving, it is almost necessary if you want to complete the class in a reasonable amount of time. You have to use your head about it to decide how much is too much.

 

[Winstone]

Ok so my thinking is that keeping to 10mins of deco would keep within sensible limits while maintaining at least 1hr of surface interval?

 

[Subcooled]

I am not the most knowledgeable guy on these issues, but I will try to answer.

We have tables and computers to calculate mandatory decompression stops.

More dives is of course more risky, as there are bubble dynamics that are included in some models and not in others and the topic is controversial.

There are other things to consider too, such as hydration status, physical shape, fat, age, exercise after the dive (=bad) and so on.

 

[DiveLikeAMuppet]

Two decompression dives are pretty common on boats in Scapa Flow but the surface interval is 3 - 4 hours. The deco is not horribly long due to cold and boat logistics - you don’t want to miss lunch. When I was there I limited myself to max 3 hours runtime per day and max 60 minutes of deco per day, which seemed to work but that was just a rule of thumb and similar to other divers. It was also on a unit so the quality of deco was pretty nice due to stable PPO2.

I do and have seen other people do a deco dive (20ish minutes) followed by a shallower no-stop dive with very short surface interval of 1 hour.

I probably wouldn’t do two massive dives per day - but I’ve never been tempted yet… The main problem is that Buhlmann probably hasn’t been tested for repetitive dives all that much.

 

[rjack321]

I've done 2x 180ft+ dives in a day in the Great Lakes. Roughly 100 minute SIs and GF 50/75. I usually pad the deco down to 65-70 surfacing high though.

 

[boulderjohn]

The main problem is that Buhlmann probably hasn’t been tested for repetitive dives all that much.

Why would you make that assumption? Are you talking about test conditions or simply by the dives people have been doing for decades?

 

[boulderjohn]

Ok so my thinking is that keeping to 10mins of deco would keep within sensible limits while maintaining at least 1hr of surface interval?

I'd typically be doing more than 10 minutes of deco and also more than a 1 hour surface interval.

 

[nadwidny]

2 x 150-200' dives per day is pretty standard in the Great Lakes and Bikini. Bikini was 2 hour-ish run times. 4 hour surface interval is mandatory with Dirty Dozen on their Bikini and Truk trips. I think we did 90 minute run times (because of the cold) with 90 minute surface intervals in the Great Lakes.

 

[Rich1280]

I've done 2x 50-55m dives per day for a 3-4 days at a stretch, then a day down to one dive and then carry on with 2 to see the week out. SI was usually at least 2 hours though, and dives were usually about 30 minutes of deco, so not massive dives. Was a good way to see the wrecks in Croatia. Didn't feel too bad on it either, not super sleepy or sub clinical.

Similar to Dives like a Muppet, my Scapa weeks have been two decent deco dives a day, but again 30 minutes of deco per dive is about all you'll want realistically to make sure you don't miss lunch, and that feels fine too. There is the common view in Scapa though that the chamber is busy on Thursday as everyone loads up with nitrogen and gets the hit on day 5 of diving if they're going to get it by not being sensible.

Rich