Your Gradient Factors?

[beester]

I’m sure someone will correct me in this if I’m wrong. But surely no dive computer builder will allow a user to make an adjustment that might bend them and built into every computer is a ceiling that you don’t go above without deco. So people are playing around with minimum deco and max deco. And any adjustments to the gradient factor is just playing around at the edges?

The GF part has already been answered. The computers I use (both on rebreather and for OC) try to keep you safe but they will keep calculating an ascend even if you dangerously change the parameters.

For example I also use a computer as gauge (depth and time). I've had times where I forgot to change my breathing gas from last dive (deco on O²) back to a trimix gas. So then you arrive at the bottom breathing your trimix mix but your computer still has O² as breathing gas set. Yes you'll see bright red warnings flashing your PPO² stating you are about to die ;-) but it will keep calculating a 60m dive even if you keep the settings on pure 100% O². Same with missing deco stops. If I elect to skip a stop, or just drop the last 5 minutes of the last stop and go up, it will warn me that I'm missing stops, but if I confirm this it will keep calculating, instead of crashing out.

I really like this...

 

[boulderjohn]

If I elect to skip a stop, or just drop the last 5 minutes of the last stop and go up, it will warn me that I'm missing stops, but if I confirm this it will keep calculating, instead of crashing out.

Yes, and it important to know before selecting a computer that not all will do this. Some will go into gauge mode in mid dive if they do not like your profile, and then you have no guidance whatsoever.

 

[boulderjohn]

I've seen it in some DAN EU study that I'm pretty sure did not include deco dives and I should've highlighted and stressed no-stop up there. Although ZH-L16 was "adjusted" from A to B to C also in the middle compartments, and that was after the trials. Or at least A to B was I believe.

Note that this is only how numbers work out. How much faith an actual diver should put in them for actual deco is another story.

I read the study as well, although for the life of me I cannot find it right now. It was very recent. IIRC, it hypothesized from DCS results that algorithms in general do not allow enough time for middle tissue off-gassing. It also said, unsurprisingly, that personal differences in physiology were major factors.

 

[scubadada]

I read the study as well, although for the life of me I cannot find it right now. It was very recent. IIRC, it hypothesized from DCS results that algorithms in general do not allow enough time for middle tissue off-gassing. It also said, unsurprisingly, that personal differences in physiology were major factors.

Frontiers | Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base | Psychology (frontiersin.org)

 

[scubadada]

Frontiers | Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base | Psychology (frontiersin.org)

I believe this article came to my attention when it was posted by @stepfen Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving

It is a very interesting read, I recommend it. Nearly 74% of 320 cases of DCS occurred at GFs from 0.7-0.9 (a little over 18% even lower). Nearly 76% of cases of DCS involved the medium tissues, 5 and 6, half lives of 27 and 38.3 min respectively.

Considerable food for thought

 

[NothingClever]

Yes, and it important to know before selecting a computer that not all will do this. Some will go into gauge mode in mid dive if they do not like your profile, and then you have no guidance whatsoever.

I still dive with a slate in the 1:1,000,000 chance my Perdix fails.

 

[tursiops]

Nearly 74% of 320 cases of DCS occurred at GFs from 0.7-0.9 (a little over 18% even lower).

I don't know how to interpret this without also knowing how many dives did NOT have DCS that used GFs from 0.7-0.9; that is, what is the denominator?

 

[boulderjohn]

I still dive with a slate in the 1:1,000,000 chance my Perdix fails.

For decompression dives, you are absolutely supposed to carry some sort of redundancy. If you are only going to use one computer, then your dive should have been preplanned, with at least 3 possible ascent scenarios written out. You would also need to have methods to measure depth and time as well.

 

[boulderjohn]

I don't know how to interpret this without also knowing how many dives did NOT have DCS that used GFs from 0.7-0.9; that is, what is the denominator?

I am sure they have those details. The article article gives enough information to get a good idea.

The DAN DB analysis shows that most dives were made in a “safe zone,” with an average depth of 27.1 m, average GF 0.66, and an average ascent speed lower than the currently recommended “safe” one. Even more importantly, very few deco omissions occurred; this indicates that divers tend to dive very conservatively.​

I have frequently heard or read the phantom statistic that 50% of all DCS cases happen when the diver is within NDLs. Well, in this study, 97.5% of all DCS cases occurred with the divers staying within NDLs. Apparently it is pretty rare for NDL divers to violate their computer algorithms, so the overwhelming majority of DCS cases occur within NDLs.

 

[Celt]

The GF part has already been answered. The computers I use (both on rebreather and for OC) try to keep you safe but they will keep calculating an ascend even if you dangerously change the parameters.

For example I also use a computer as gauge (depth and time). I've had times where I forgot to change my breathing gas from last dive (deco on O²) back to a trimix gas. So then you arrive at the bottom breathing your trimix mix but your computer still has O² as breathing gas set. Yes you'll see bright red warnings flashing your PPO² stating you are about to die ;-) but it will keep calculating a 60m dive even if you keep the settings on pure 100% O². Same with missing deco stops. If I elect to skip a stop, or just drop the last 5 minutes of the last stop and go up, it will warn me that I'm missing stops, but if I confirm this it will keep calculating, instead of crashing out.

I really like this...

Do you mind me asking what computer you use