Deep Stops Recreational Divers

[rjack321]

Under the right conditions that ascent rate would be harmful. Could those conditions be met on a rec dive??????

I've seen 200ft/min done on rec dives. Essentially corking from 40ft in 10-15seconds. I'd say that's outside of any tested model but at least on a 40ft dive your embolism risk probably exceeds your DCS risk.

 

[scubadada]

Because in my case I reduce pressures more gradually and 15ft sucks when its surgy or wavey or most times on CCR. Vis at 20-30ft is usually way better than 15ft, so you can see and communicate better too.

You take 2.6 mins to reduce from 4 to 1.5 ata
I take about 4 mins to reduced from 4 to 1.5 ata (by the time I get to 15ft)
I don't think there's any reason 1.5-2 mins deeper than 15ft is remotely relevant from an offgassing perspective.

30ft is still well within the offgassing zone for faster tissues and on 32% the slow tissue ongassing at anything less than ~45ft is so negligible you have for all practical purposes infinite NDL time. I don't know anyone rushing up to 15ft to hang around here, even on a boat dive coming up an anchor line. Definitely not on shore dives where there's stuff to see at 20ft since its often below the wave action zone.

So, it's because you like to. You don't like the surge at 15 ft, so you do 2 min at 10 ft. Vis has nothing to do with it, you do 2 min at 20 ft and the 2 min at 10 feet.

Maybe it's because your home diving is WA, mine is mostly reef drift diving in FL

 

[MargaritaMike]

For communication to be successful, you have to have the common sense to understand a word in the meaning it was intended to convey, not another meaning that results from your preferred definition of the key terms.

But remember, John, common sense is uncommon.

Cheers -

 

[NAM001]

I've seen 200ft/min done on rec dives. Essentially corking from 40ft in 10-15seconds. I'd say that's outside of any tested model but at least on a 40ft dive your embolism risk probably exceeds your DCS risk.

I agree... you have to really try to get hurt on a legit rec dive. any precaution at all and you make it up safe. A deep stop should not even matter unless you tried to do a max +++++ascent rate to 1/2 pressure and lost depth control and then thats IFFY. I am sure it can be done though with effort.

 

[rjack321]

So, it's because you like to. You don't like the surge at 15 ft, so you do 2 min at 10 ft. Vis has nothing to do with it, you do 2 min at 20 ft and the 2 min at 10 feet.

Maybe it's because your home diving is WA, mine is mostly reef drift diving in FL

Yea and if I wanted to I could skip the safety stop. Back when I was a 30 dive diver I corked from 15ft plenty of times (and back then ascent rates were 60ft/min too, so it was maybe a 2min ascent from a 50-60ft dive). And I cant tell you how many times I corked from 15ft on CCR when I was starting out. You all are making safety stop out to be some sort of precise thing. Even DAN has said their primary function is to slow down divers in the last (and largest) region of pressure changes. They aren't about offgassing ala a deco stop. 3 mins is inconsequential for offgassing, its about moving slow near the surface as the pressure drops the most.

 

[KenGordon]

...running a version of RGBM, which is inherently deep stop in its design.

Why do you think that Suunto RGBM is a version of RGBM, and so a bubble model calibrated to give deep stops? Surely if it were it would not need to introduce them in the style of Pyle stops as this computer does.

Have a read of http://www.dive-tech.co.uk/resources/suunto-rgbm.pdf which describes Suunto RGBM, it includes a lot of things that are features of a regular dissolved gas model.

“The Suunto RGBM assumes that the human body is divided into 9 major tissue compartments, which are based on the rate at which each tissue group on- or off-gasses. These half-times range from 2.5 to 480 minutes.”

And, following a description of the mitigations against repetitive diving, short SIs etc,

“The combination of the correction factors is applied to the Suunto RGBM’s M-values thus reducing the permitted supersaturation gradient, which adjusts the required decompression obligation.”

My bold.

I have two Suunto computers, the HelO2 and a Zoop. The Zoop doesn’t add these Pyle deep stops but I is still Suunto RGBM (the Helo2 is Suunto Technical RGBM, but I think that just allows more aggressive settings). I recall I have had stops as deep as maybe 13m with the Zoop, using it as a backup bottom timer on a 60m dive using two deco gases.

I wrote an implementation of Bühlmann GF from scratch as an aid to understanding it myself, it works (ie, gets the same answers as Ross) and so I believe I understand how a gas content model works.

For my reading of what Suunto say, and from my observation of how the Suunto computers work on deco dives, I think that they have a gas content model with some minor modifications to the limits which are supposed to limit bubble growth. I don’t think there is any ‘deep stop’ inherent in the design.

 

[rongoodman]

Why do you think that Suunto RGBM is a version of RGBM, and so a bubble model calibrated to give deep stops?

Why wouldn't you, since they chose to use the name in their advertising? The problem is that no one really knows what it is, or how it varies across their product line.

 

[scubadada]

Yea and if I wanted to I could skip the safety stop. Back when I was a 30 dive diver I corked from 15ft plenty of times (and back then ascent rates were 60ft/min too, so it was maybe a 2min ascent from a 50-60ft dive). And I cant tell you how many times I corked from 15ft on CCR when I was starting out. You all are making safety stop out to be some sort of precise thing. Even DAN has said their primary function is to slow down divers in the last (and largest) region of pressure changes. They aren't about offgassing ala a deco stop. 3 mins is inconsequential for offgassing, its about moving slow near the surface as the pressure drops the most.

Hi @rjack321

I was certified by LA County in 1970, ascent rate was 60 ft/min, there were no safety stops, we used USN tables for NDLs. Most of us did just fine diving in Southern California.

Today, you are still able to ascend directly to the surface from a no stop dive, the ascent rate is slower, the safety stop is optional. In my 49th year of diving, I'm more conservative than I used to be, I'd like to continue diving as long as I'm able. I still dive relatively aggressively. I do a 3-5 minute safety stop on a no stop dive and pad my stop by 3-5 minutes when I do light deco. Either of these practices will lower my surfacing GF compared to a direct ascent (perhaps someone with an appropriate computer can tell me by how much). So far, so good We all end up doing what we want, based on the information available to us and how we choose to interpret and use it.

Good diving, Craig

 

[tursiops]

I'm sympathetic to the points being made about recreational diving being full of ways to keep from hurting yourself, and the marginal benefits that come from small adjustments like deep stops, exact depth of a safety stop, etc, are, well, marginal. Any safety stop of 1 minute or more in the 20-10 ft range is fine and is going to provide most of the benefit, it seems; 3 mins is better than 1 (marginally), 5 better than 3 (marginally), etc.

Having watched lots of recreational divers, I'd say the most dangerous thing I routinely see is a very fast ascent from the safety stop to the surface. At 30 ft/min, it ought to take 30 secs to go from 15 ft to the surface. If it only takes 10 seconds, that's 90 ft/min. 5 secs is 180 ft/min. So 200ft/min? I'd say that's pretty common, not rare. Scary. So the safety stop becomes REALLY important, because it allows the tissues to try and offgas enough that the almost-instantaneous release of pressure from that fast 15-ft ascent has less dissolved gas to allow to bubble. Now, 3 mins becomes REALLY important, and 5 minutes is even better.

 

[boulderjohn]

Why do you think that Suunto RGBM is a version of RGBM, and so a bubble model calibrated to give deep stops?

Well, let's start with the fact that using the term "RGBM" to describe something that is not RGBM would begin a lawsuit. It has been years since I saw the description of the HelO2, but IIRC, it specifically used Bruce Wienke's name in that description. What happens in it exactly? I don't know. That information is proprietary. It just seems to me that if it says the algorithm is Bruce Wienke's RGBM, it is probably a version of Bruce Wienke's RGBM.