When to do a safety stop?

[Scuba_Nick27]

Gotcha. You may have been editing while I was posting.

I still see the stop at 30 feet in your post. That does not sound like a safety stop, but more like a deep stop. Usually the target depth is around 15 feet, though the acceptable range usually runs between 20 ft to 10 ft, but can vary between computers.

Yes. Deep stop. I mean, it is a safety stop just half the total depth.

 

[Scuba_Nick27]

Gotcha. You may have been editing while I was posting.

I still see the stop at 30 feet in your post. That does not sound like a safety stop, but more like a deep stop. Usually the target depth is around 15 feet, though the acceptable range usually runs between 20 ft to 10 ft, but can vary between computers.

I read a study that says that gas escapes tissues at exponential levels based on depth and pressure. So if your max depth was 60 feet and you stay there for 30 minutes, you will have to stay at 30 feet for 5 minutes min. and then stay at 15 feet for atleast 3 to ensure that the gas levels in your tissues are equal. If you don't, then you won't really feel any difference.

 

[Belzelbub]

I read a study that says that gas escapes tissues at exponential levels based on depth and pressure. So if your max depth was 60 feet and you stay there for 30 minutes, you will have to stay at 30 feet for 5 minutes min. and then stay at 15 feet for atleast 3 to ensure that the gas levels in your tissues are equal. If you don't, then you won't really feel any difference.

It’s not quite as linear as that. Different tissues on gas and off gas at different rates. The Buhlmann ZHL-16C algorithm (used by Shearwater and several other computers) tracks 16 different tissue compartments. Tracks is not the right word, it’s more like a prediction. The slow tissues are always lagging. A deep stop can be beneficial for fast tissue offgassing, while contributing to more ongassing by the slow tissues. It would all depend on the actual parameters of the dive.

However, at a max depth of 60 feet, it’s probably not going to matter much either way. Assuming of course that the dive is well within the NDLs.

 

[Scuba_Nick27]

It’s not quite as linear as that. Different tissues on gas and off gas at different rates. The Buhlmann ZHL-16C algorithm (used by Shearwater and several other computers) tracks 16 different tissue compartments. Tracks is not the right word, it’s more like a prediction. The slow tissues are always lagging. A deep stop can be beneficial for fast tissue offgassing, while contributing to more ongassing by the slow tissues. It would all depend on the actual parameters of the dive.

However, at a max depth of 60 feet, it’s probably not going to matter much either way. Assuming of course that the dive is well within the NDLs.

Yeah exactly. I tried finding the study but i cant. Basically, it averaged the tissues and one deep stop + safety stop turned out to be the way to go. But its not that important if you didnt stay down long enough

 

[dmaziuk]

Yeah exactly. I tried finding the study but i cant

Try wikipedia. However it does not mean what you seem to think it means: it is the basis for the formulae running inside your dive computer. The half-depth stop is something entirely different.

 

[Scuba_Nick27]

Try wikipedia. However it does not mean what you seem to think it means: it is the basis for the formulae running inside your dive computer. The half-depth stop is something entirely different.

No it's not even a computer algorith. It is a legitimate, physical study done on divers in late 1980s by ... im pretty sure, may be wrong... the american and french navy

 

[boulderjohn]

No it's not even a computer algorith. It is a legitimate, physical study done on divers in late 1980s by ... im pretty sure, may be wrong... the american and french navy

I studied the theory of deep stops in recreational dives in some depth last year. I have no idea what you are talking about in terms of this study. Yes, there are people that advocate stopping at half maximum depth, but they have little to no research to base that on.

 

[dmaziuk]

Well it's not the algorithm, it's the very basic model of gas exchange. The rate is log(2) -- logarithm is the inverse of the exponent, so dep. on how you draw it you can call it logarithmic or you call it exponential. Wikipedia page on decompression theory has it as log curve:

 

[Scuba_Nick27]

I studied the theory of deep stops in recreational dives in some depth last year. I have no idea what you are talking about in terms of this study. Yes, there are people that advocate stopping at half maximum depth, but they have little to no research to base that on.

I read the study a good while ago. I just dont remember much so dont expect me to accurately recall info lol

 

[scubadada]

I read the study a good while ago. I just dont remember much so dont expect me to accurately recall info lol

Please check your background data before posting something that may not be correct and may be misleading

I do not know this topic as well as @boulderjohn but have read extensively on the issue. I have never read anything similar to your posts. Perhaps you are thinking about the 2004 article by Marroni and colleagues published in Undersea and Hyperbaric Medicine. This is the most commonly cited study to support deep stops in no stop diving, along with a followup study from 2007 by Bennett and collaborators in the same journal. This work was executed by DAN Europe.