Diving with gradient factors for a new recreational diver

[tursiops]

A simple strategy to decrease DCS risk is to set your computer for air while using Nitrox.

This is really old advice. Just staying away from NDL will accomplish the same thing without lying to your computer.

 

[dmaziuk]

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In VERY simple terms, the problem is faster tissues will be off-gassing diluent while slower tissues can still be in-gassing during a delayed ascent. Avoiding getting bent is a balance between these conflicting factors.

On recreational dives you're simply not going to be down there long enough to load slow tissues. In DSAT testing schedules it took them 6 days to load the 120-minute compartment to near its M0 and the 480-minute one never got anywhere close. Extrapolating to ZH-L16, its 187-minute 11th TC is a bit of an if, and 12..16th ones may just as well not exist at all for recreational diving.

Edit: not to say that this isn't a concern -- on the kind of dives that require decompression on a separate gas -- but for us vacay divers... meh.

 

[HomeBarista]

On recreational dives you're simply not going to be down there long enough to load slow tissues. In DSAT testing schedules it took them 6 days to load the 120-minute compartment to near its M0 and the 480-minute one never got anywhere close. Extrapolating to ZH-L16, its 187-minute 11th TC is a bit of an if, and 12..16th ones may just as well not exist at all for recreational diving.

I remember seeing some DCS research in which they observed the large portion of cases to be related to medium tissues. If I remember right, diving buhlmann, no idea what profiles. Definitely an area for future research. Might be useful to adjust the safe limits for those tissues.

 

[dmaziuk]

I remember seeing some DCS research in which they observed the large portion of cases to be related to medium tissues. If I remember right, diving buhlmann, no idea what profiles. Definitely an area for future research. Might be useful to adjust the safe limits for those tissues.

In other ground-breaking research they observed water to be wet.

(Because the fast compartments are just that: fast, they off-gas a lot during ascent and safety stop, and the slow ones don't matter, guess which TCs are left to drive the DCS on recreational dives.)

 

[doctormike]

I remember seeing some DCS research in which they observed the large portion of cases to be related to medium tissues. If I remember right, diving buhlmann, no idea what profiles. Definitely an area for future research. Might be useful to adjust the safe limits for those tissues.

I'm not sure about what you are referring to, and I'm definitely NOT a DCS expert. But I think that you are confusing two things.

Tissue compartments don't correspond to actual physical anatomical sites. They are a mathematical model that takes into account that some tissue takes up and releases dissolved gas faster than others. But it's not like a doctor can look at you and say "aha, you got a hit in compartments 3-5".

Depending on the profile, one of the compartments will be leading, that is, the controlling compartment that has the greatest overpressure.

 

[Akimbo]

This is really old advice. Just staying away from NDL will accomplish the same thing without lying to your computer.

Sometimes, but not always. All things being equal, including not pushing NDLs, breathing lower diluent mixes will always reduce diluent absorption. The advantage of lying to your computer is the advantage is calculated over the entire time/depth range of dive profiles.

On recreational dives you're simply not going to be down there long enough to load slow tissues.

This is the problem with relative terms. "Slow" tissues are not the same thing as "slower" tissues, which is what I wrote. The slowest tissues are primarily of of concern to saturation divers. In a recreational context, slower tissues are any below the very fastest.

 

[dmaziuk]

I'm not sure about what you are referring to, and I'm definitely NOT a DCS expert. But I think that you are confusing two things.

I remember that paper, I think it was one of DAN Europe ones. Possibly the one that conflated a small database of DCS cases of unknown origin and a very large set of questionnaires filled by recreational divers who never got bent, in one "study".

 

[tursiops]

I remember seeing some DCS research in which they observed the large portion of cases to be related to medium tissues. If I remember right, diving buhlmann, no idea what profiles. Definitely an area for future research. Might be useful to adjust the safe limits for those tissues.

You know, if you are going to "quote" stuff like this, you really do need to provide citations. Otherwise it is just memory and hearsay. I guess blurting it out goes with overthinking the issues? You've been repeatedly told by those with the background and experience that you have much bigger things to worry about than DCS. So focus on those,...and get some diving in.

 

[rjack321]

Yup, was about to write what @boulderjohn said. The only way I can think of for someone to have an acquired PFO would be trauma, in which case DCS would be the least of your concerns!

You can acquire a pulmonary shunt later in life though, which also allows a bubble to pass into arterial blood similar to a PFO.

 

[rjack321]

I remember seeing some DCS research in which they observed the large portion of cases to be related to medium tissues. If I remember right, diving buhlmann, no idea what profiles. Definitely an area for future research. Might be useful to adjust the safe limits for those tissues.

Are you sure diving is for you? You seem REALLY concerned about established recreational diving practices which have a very low rate of DCS already (1: 4 to 8,000 dives roughly). This is far lower than the injury rate for almost any other outdoor activity.