Deco Setpoint

[JonG1]

Firstly I have tried searching but for some reason the search function is not operational and prior threads that come back from google are 404.

A few of us were diving normoxic wrecks over the weekend at circa 50-60m and there was some discussion about whether to bump up the set point on deco, either to accelerate it or to improve conservancy by doing the same stop durations as indicated whilst on 1.3 but with a higher setpoint (circa 1.4-1.5).

Obviously there are due considerations regarding cell health and accuracy at the end of a dive with humidity levels in the unit etc. and CNS percentages, but generally what is current thinking on this.

 

[rjack321]

1.2, 1.3, 1.4 makes very little difference on a 60m wreck dive. The majority of the offgassing is driven by the pressure gradient not the ever so slightly different fO2 in the loop

 

[Wibble]

Whilst at decompression with a significant time to go, e.g. over an hour, changing the setpoint from 1.2 to 1.4 makes a significant difference to the TTS, over 10 mins.

 

[Vicko]

Realistically speaking you only have 3-4 deco stops bellow 12 meters and above that holding anything over 1.4 becomes a pain in the ass.

 

[cathal]

Most people I know, will, as soon as the ascent starts, manually bump up the O2 to 1.5.
Also, at the 6M stop, about every 40 minutes or so, they will do a complete loop flush with O2.

 

[JonG1]

Most people I know, will, as soon as the ascent starts, manually bump up the O2 to 1.5.
Also, at the 6M stop, about every 40 minutes or so, they will do a complete loop flush with O2.

What's the rationale on the flush Cathal and is the 1.5 to improve the efficiency of the deco or reduce the time to surface.

 

[kensuf]

I typically run 1.2 on the bottom and 1.3 on deco until I get to 6m, then I'll do an O2 flush to check cell health and let it decay from there to around 1.4. I may run 1.0 on the bottom if it's going to be an exceptionally long dive (>3 hours).

 

[tbone1004]

I typically run 1.2 on the bottom and 1.3 on deco until I get to 6m, then I'll do an O2 flush to check cell health and let it decay from there to around 1.4. I may run 1.0 on the bottom if it's going to be an exceptionally long dive (>3 hours).

similar, though on a normoxic dive I would flush with 50% at 70ft/20m and that way I could check the cells at 1.5-1.6 and be comfortable running them up that high. I typically run 1.1-1.2 on the bottom as well which is close enough to the 1.0 that I calibrated against that I'm happy. 1.5-1.6 is too far away and too risky for the funky chicken for me to head over to without a dil flush to check.

 

[beldridg]

A few of us were diving normoxic wrecks over the weekend at circa 50-60m and there was some discussion about whether to bump up the set point on deco, either to accelerate it or to improve conservancy by doing the same stop durations as indicated whilst on 1.3 but with a higher setpoint (circa 1.4-1.5).

I'm not sure how you would realistically and easily do the same stop durations.

Let's say you get to your 40' stop @ 1.3 and it is 6 minutes. You then bump up to 1.4. As you do that your computer would then decrease the stop time based on 1.4 (which wouldn't be a big change as another poster mentioned). Do you then remember the original stop time and stay at the 40' stop until the "clock" has reached that even though you have cleared the 40' stop?

And then when you get to 30' do you bring it back down to 1.3 to see what the stop duration would be and then repeat the process?

Or do you use an off board computer with an internal set point of 1.3 and do the stops indicated on that and not on the computer connected to the cells which is presumably at 1.4?

Maybe I'm just misunderstanding what you mean by "doing the same durations as indicated whilst on 1.3?"

- brett

 

[Wibble]

The discussion was about increasing the setpoint (at deco) and whether there's any issues arising from this, aside from the benefits of a shorter TTS.

Answers to include references to conservatism and risk assessments. Would be good to get references to current thinking.