Can you do too much deco?

[DeepSeaExplorer]

Once you’ve met your deco obligation, you can switch to back gas and do some extra deco. That gets you off O2 and gives you a greater safety margin.

If using up helium is an issue, you could switch back to your deeper deco gas, assuming you’re carrying two deco gases.

 

[RedSeaDiver2]

As said above, short answer is no however I would seriously re-evaluate your GF's as they are out of whack with currently accepted balance of GF. If you want a high of 60 then I would have a low of around 50 not 30. 45 at the lowest. The balance between low and high is coming into higher prominence in discussions with many diving a low somewhere around 80% of the high after several studies over the last few years.

What many of us personally do/recommend is choose our profile that we are happy with, for me on a 60m warm dive that would probably be 70/85 or 60/80 depending on how much fun we had the night before and once I got up to 30-20-10ft range, then hang out for a while. If I'm on a line just hanging in the middle of the ocean I have to admit that that probably wouldn't be a very long time but if there was something to do or look at then I am prone to nearly draining my tanks before I get out of the water. Don't forget low ppO2 gas breaks *air breaks but no one I know actually carries air anymore so it's some sort of a low ppO2 break*, and if you finish your deco on the "normal" gf's and are just hanging out for good measure then you can switch to a less harsh gas for the remainder of your time in the water that will still have you offgas but less likely to cook your lungs. A 60m dive should have 50% on there so you can stay on that until it is empty without having to worry about switching again.

If you have a Shearwater the surfGF function is quite convenient and if you want to get out at a gfHi of 60, just chill out until the surfGF is 60 *which will take a hot minute* but no need to set the actual ascent profile that low because it will give you a weird profile and if something goes sideways you may be in more trouble than you're attempting to save.

The diving will be on CCR, using a high helium% mix, there isn't any intention to swap gases during the ascent. Unfortunately the deco will be hanging in the middle of the blue.

 

[L13]

The diving will be on CCR, using a high helium% mix, there isn't any intention to swap gases during the ascent.

Just drop the PO2 setpoint for the "extra" time after deco is done. Effectively the same as @tbone1004 's advice. Instead of "use up the rest of your tank" it is now "use of the rest of your sorb time(since you are going to change it before next dive anyway)."

 

[RedSeaDiver2]

Just drop the PO2 setpoint for the "extra" time after deco is done. Effectively the same as @tbone1004 's advice. Instead of "use up the rest of your tank" it is now "use of the rest of your sorb time(since you are going to change it before next dive anyway)."

Sounds like an option.

 

[leadduck]

Remember that your last deco stop is not 3m but 0m, and it's a very important one. Make sure you decompress well right after surfacing; exit slowly, take a good rest, hydrate. That'll make a bigger difference than just minimizing GFhigh far below what your body actually needs, which again depends on your body and experience. Also consider that warm water is not necessarily an advantage. Are you working at depth ("archeological dive") in warm water? That would be a reason to reduce GF below what you usually are happy with.

 

[RedSeaDiver2]

Remember that your last deco stop is not 3m but 0m, and it's a very important one. Make sure you decompress well right after surfacing; exit slowly, take a good rest, hydrate. That'll make a bigger difference than just minimizing GFhigh far below what your body actually needs, which again depends on your body and experience. Also consider that warm water is not necessarily an advantage. Are you working at depth ("archeological dive") in warm water? That would be a reason to reduce GF below what you usually are happy with.

We will certainly be taking it very easy on the boat afterwards - that is something that I always emphasise to other divers. Last underwater stop has to be at 6m due to the ocean conditions - unfortunately this wreck decided to go down in open ocean rather than a nice calm spot behind a reef. Will be working at depth - basically kneeling on the bottom a lot of the time.

 

[leadduck]

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.

 

[tbone1004]

The diving will be on CCR, using a high helium% mix, there isn't any intention to swap gases during the ascent. Unfortunately the deco will be hanging in the middle of the blue.

I would suggest you reconsider not swapping gases on ascent. You should have 50% with you anyway for bailout deco and switching to that at 70ft/20m is going to greatly expedite your ascent profile....

 

[RedSeaDiver2]

I would suggest you reconsider not swapping gases on ascent. You should have 50% with you anyway for bailout deco and switching to that at 70ft/20m is going to greatly expedite your ascent profile....

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

 

[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 a good suggestion, will run the numbers for that in MultiDeco to see what it gives - thanks!