Can you do too much deco?

[tbone1004]

On bailout it would, but I haven't seen many people advocating using 50% as a CCR Dil during ascent. Carrying 50% is in the bailout plan

Many do gas switches into the CCR as if they were bailing out. Especially useful if you have a BOV

 

[GF99/99]

On bailout it would, but I haven't seen many people advocating using 50% as a CCR Dil during ascent. Carrying 50% is in the bailout plan

I dil switch to 50% all the time. Also at 18m its a really nice gas to do cell checks with and usually a great time to bump up to 1.4

On sub 100's usually do two dil switches and sub 160's 3 dil switches

Just make sure your are aware of ICD (but that is an entirely sperate controversial topic)

 

[RedSeaDiver2]

Just make sure your are aware of ICD (but that is an entirely sperate controversial topic)

ICD - that's another can of controversial worms. Fortunately with a depth of only 65m it is less of a problem.

 

[scubaozy]

I recently bumped into a documentary of an expedition/research done in Mediterranean, basically 28days of saturation diving. It is in German but perhaps later you can find translated versions. Images are pretty stunning and the concept they use would be very suitable for the archeology.

 

[RedSeaDiver2]

For working dives, there's a different traditional method that you may have a look at. The effect of workload is faster on-gassing at depth by better perfusion, which is similar to longer bottom time in a non-working dive. In the old tables you would read at 1.5x bottom time for working dives. So instead of guessing a reduced GF, you could enter a 1.5x longer bottom time into MultiDeco, e.g. for a 20min working dive calculate an ascent with 30min bottom time and your usual GF. Comparing that ascent to your other results with reduced GF will give you an idea what GF reduction is compatible with +50% faster on-gassing due to workload.

That is giving some interesting results, using my normal GF and 1.5x longer working time results in an extra 26 minutes of decompression required which pushes CNS to 100.9% (when compared to the planned working time and a GF of 30/60). Trying to get a matching profile for the 1x dive seems rather difficult - 50 isn't low enough for the upper GF.

 

[leadduck]

That is giving some interesting results, using my normal GF and 1.5x longer working time results in an extra 26 minutes of decompression required which pushes CNS to 100.9% (when compared to the planned working time and a GF of 30/60). Trying to get a matching profile for the 1x dive seems rather difficult - 50 isn't low enough for the upper GF.

Funny, isn't it? But +50% more perfusion is not excessively pessimistic for a strenous working dive in warm water. Looking at DCS incidents statistics, exertion at depth such as swimming against a current is a major contributing factor to "undeserved" hits, indicating that this problem is underestimated by many divers and some of these hits are actually well deserved ... Be aware that you have a potential major DCS risk factor here.
Practically, I can't tell how to best manage this. I wouldn't care about CNS exceeding 100%. Obviously, observe heart rate and breathing at depth, always move slowly. Maybe you want to keep two runtime tables in your wetnotes, and pick the extra conservative one when you feel that you had a lot of work to do?
A cheap underrated trick may be surface oxygen, i.e., back on the boat relax on the sofa breathing O2 preventively for like 30min right after a working dive that may or may not have you loaded with an unexpected high amount of inert gas, to get rid of it more quickly before it bites you. YMMV. Other ideas?

 

[RedSeaDiver2]

I recently bumped into a documentary of an expedition/research done in Mediterranean, basically 28days of saturation diving. It is in German but perhaps later you can find translated versions. Images are pretty stunning and the concept they use would be very suitable for the archeology.

Looks like I'm out of luck -

 

[RedSeaDiver2]

Funny, isn't it? But +50% more perfusion is not excessively pessimistic for a strenous working dive in warm water. Looking at DCS incidents statistics, exertion at depth such as swimming against a current is a major contributing factor to "undeserved" hits, indicating that this problem is underestimated by many divers and some of these hits are actually well deserved ... Be aware that you have a potential major DCS risk factor here.
Practically, I can't tell how to best manage this. I wouldn't care about CNS exceeding 100%. Obviously, observe heart rate and breathing at depth, always move slowly. Maybe you want to keep two runtime tables in your wetnotes, and pick the extra conservative one when you feel that you had a lot of work to do?
A cheap underrated trick may be surface oxygen, i.e., back on the boat relax on the sofa breathing O2 preventively for like 30min right after a working dive that may or may not have you loaded with an unexpected high amount of inert gas, to get rid of it more quickly before it bites you. YMMV. Other ideas?

I think that many "undeserved" DCS hits actually have quantifiable causes or contributing factors that haven't been recognised. In the Red Sea a big one is dehydration - simply because the air is so dry that your sweat evaporates before you notice it and so you don't realise how much fluids you are losing. I drum into people a variation on an old Johnny Nash song - it becomes "I can pee clearly now - even though it is a bright bright sunny day".
One of the ways to reduce bubbling will be the use of a boat with a diver lift instead of having people climb up a ladder, and agree with you about surface O2.
The tasks to be accomplished on each dive will be carefully briefed, and I will be keeping an eye out for any task that requires excessive exertion - divers doing those tasks might have their bottom time limited to 15 minutes but they are required to do the full decompression plan of a 23 minute dive.

 

[Johnoly]

I think that many "undeserved" DCS hits actually have quantifiable causes or contributing factors that haven't been recognised.

With the profiles, teams and months of dives, why not skip the entire daily decompressions and instead just switch to full saturation diving. There's lots of commercial dive boats setup for it and would be alot safer.

 

[RedSeaDiver2]

With the profiles, teams and months of dives, why not skip the entire daily decompressions and instead just switch to full saturation diving. There's lots of commercial dive boats setup for it and would be alot safer.

Totally - but to train archaeologists all the way through commercial diving to sat diving level...