Deep Safety stops

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Deep Safety stops

Postby aquakiwi » Thu Jun 11, 2009 8:09 pm

I'm not really familiar with them but understand they can be beneficial, at what depth? and can they take the place of the 5m stop.
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Re: Deep Safety stops

Postby NEMES1S » Thu Jun 11, 2009 8:35 pm

Well I have used them complimentary to the 5m stop (Diving at the Knights and also White Island with Pete, and the Waikato with Andy),my Gekko PC doesnt vector Deep Stops into my dive profile but recently with Andy his VYTEC did so we did a 2min stop at 15m on the Waikato.
Normally our dives are shore dives so dont merit the "Deep Stop"...

Deep stops
A "Pyle stop" is an additional short deep-water stop, which is increasingly used in deep diving (named after Richard Pyle, an early advocate of deep stops[11]). Typically, a Pyle stop is 2 minutes long and at the depth where the pressure change halves on an ascent from the bottom to a shallow water decompression stop. For example, on an ascent from a maximum depth of 196 feet (60 metres) at 100 psi (7 bar) to a decompression stop at 65 feet (20 metres) at 40 psi (3 bar), the Pyle stop would take place at the halfway pressure, which is 70 psi (5 bar) at 130 feet (40 metres).


DAN wrote:Adding A Deep Stop
On the other hand, it was found that even in repetitive dives, bubbles could be avoided as long as the leading tissue nitrogen was kept below 80 percent of the allowed M value, or less than 11 mbars (1 bar = surface pressure). The M value is the safe calculated partial pressure of nitrogen that can be safely allowed. A practical way to achieve this was by the introduction of an additional deep stop. This simple procedure lengthened the ascent time from 11.2 mins to 18.55 minutes, without changing the ascent rate, and reduced the previously recorded 30.5 percent incidence of high-grade bubbles to zero.

International DAN research studies have recently clearly confirmed these hypotheses: 15 divers were enrolled in a study and each given eight possible combinations of ascent rates, and either a shallow stop, or a deep and a shallow stop. The repetitive dives were to 80 feet (25 meters) for 25 minutes; the surface interval was three hours, 30 minutes; and the final dive was to 80 feet for 20 minutes. Ascent rates were 60, 30 and 10 feet per minute. The matrix is shown in Table 3 and the results of 181 dives are shown in Table 4.

Clearly, the best decompression schedule is Profile 6 (see highlights in both tables). With an ascent rate of 33 feet (10 meters) per minute, and two stops at 45 feet (13.5 meters) and 9 feet (2.7 meters) respectively, this profile had the lowest bubble score of 1.76.

Other Experiences with Deep Stops
From time to time in diving history, the concept of the "deep stop" has reappeared. Brian Hills noted that Australian pearl divers, who previously endured many fatalities and severe DCS in places like Broome and Thursday Island, eventually devised their own means of decompressing to stop this. The whole secret to their success was empirically adding deeper initial stops.

In more recent times, recreational technical divers have also devised their own decompression methods which have led to two so-called "bubble models" for computation. The Wienke Reduced Gradient Bubble Model (RGBM) and the Yount Variable Permeability Model (VPM) both attempt to predict when bubbles form and then calculate decompressions to prevent bubble formation before surfacing.4

NAUI technical divers have used the Wienke RGBM model quite extensively with no recorded incidence of DCS. This data as well as the results of this IDAN research in divers were discussed at a NAUI workshop in Florida in early 2003. As a result, NAUI has now suggested that a deep stop might well be incorporated in recreational diving by taking a one-minute stop at half the depth and followed by a two-minute safety stop at the 15- to 20-foor level instead of the three minutes currently recommended. We are currently testing this concept with our Italian diver research teams.


http://www.suunto.com/suunto/main/artic ... 4395903548
Last edited by NEMES1S on Thu Jun 11, 2009 8:45 pm, edited 2 times in total.
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Re: Deep Safety stops

Postby Cameron_R » Thu Jun 11, 2009 8:39 pm

A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions.
A. MARRONI1,2, P. B. BENNETT4,5, F. J. CRONJE5,7, R. CALI-CORLEO1,2, P. GERMONPRE1,6, M. PIERI1, C. BONUCCELLI1, C. BALESTRA1,3
http://www.diversalertnetwork.org/news/ ... coraut.pdf
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Re: Deep Safety stops

Postby binklebonk » Thu Jun 11, 2009 8:42 pm

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Re: Deep Safety stops

Postby Paul » Thu Jun 11, 2009 9:31 pm

Deep stops are interesting theory (by interesting I mean interesting to read about and not that I'm being sarcastic. I think they are a great idea and make alot of sense for deep bounce profiles). However I understood that they apply to dives that fit outside the recreational no-decompression limits.

I'm just wondering given the title Deep "Safety" stops, was the question about stopping deeper that 5m as a way to reduce risk for recreational "no-stop" dives, or just a general question about deep stops.

The only time my VR3 suggested a deep stop was on long dives which required a mandatory decompression stop.

One of the key principals of a deep stop is that you stop above the deepest possible decompresstion stop choice. If no tissue compartment is near the M-Value (or gradient percentage of the M-Value) then a deep stop will not make much difference. So you really need to know your profile, and what depth that "deepest possible decompression stop" is at. So if you are still in no-deco mode... then a deep stop is not going to be that much benifical I would have thought.

I'm not an expert on this stuff though, I just find it interesting and will stand corrected by superior understanding.

I ready a really good explaination recently. I'll see if I can find it.


*Edit, found the article. It's written by who appears to be knowledgeable fellow called EriK C. Baker I can't upload a PDF but you can find it here: http://www.shearwaterresearch.com/tools/software/3.0/go.php?toolscontext.publicstep=FileDownload&toolscontext.stepinput.entity=content&toolscontext.stepinput.property=FileName&toolscontext.stepinput.id=3397
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Re: Deep Safety stops

Postby aquakiwi » Tue Jun 16, 2009 9:35 am

My interest is that often in surge ecetra I find the shallow stop differcult when encumbered with bulky camera gear as I usually am, the possibility of doing a deeper stop and then possibly no shallow stop would be welcome.
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Re: Deep Safety stops

Postby Paul » Tue Jun 16, 2009 10:43 am

So the answer I think lies in an understanding of what the intention of a 5m safety stop is for. It is first of all important to note that it is not a "required" stop.
In a recreational context, it can serve two main purposes. One is to stop the ascent from depth, to allow you to get youself sorted before heading to the surface. Not having this pause can contribute to divers, especially new divers, having an uncontrolled ascent to the surfact over those last few meters, as those last few meters have the biggest change on bouyancy. So stopping at 5 meters, forces you to stop your ascent and get neutrally bouyant before heading to the surface.... slowly. Also helps to prevent lung over expansion injuries.
The other purpose is to reduce the risk of DCS. Just to re-itterate, this is not a required "deco-stop" it is a safety stop. According to the tables/computer you are not required by the algorithm to stop to off gas before heading to the surface. However, stopping for a few mins at 5M will reduce your risk even further.

So, knowing what the reasons for a safety stop in recreational diving is, you can now make more informed choices about if/when you do them. If you are in a situation that is increasing your risk of injury (such as the surge you pointed out) then doing a safety stop will in fact increase the risk. If you know in advance that it is likley to have a rough surface, then plan your dive accordingly to be even more conservative, so you are not in the situation of "needing" to do the safety stop due to being close to limits.

I have seen people do some pretty dangerouse things, all in the name of doing a safety stop :-) Kind of defeats the purpose really! If doing the safety stop puts you at greater risk than not doing it...... It all comes down to dive planning. Plan your dive and dive your plan.
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Re: Deep Safety stops

Postby Azza » Tue Jun 16, 2009 6:43 pm

I do deep stops for recreational dives and still do the 5/6 metre stop but also like to add in a 1 minute 3 metre stop if possible.

I did the figures once (a long time ago) to see if it would make a difference to the tables and the amount of extra nitrogen loading acquired was negligible. When undertaking deep dives it is your fast tissues that load up and limit the dive, while doing a halfway stop you are already offgassing those tissues and its the slower tissues that are loading up, but for the amount of time at the depth it really is negligible. Like I do 9m per minute ascent rates instead of 18...negligible.

The idea of the deep stops is more to slow your ascent, and limit bubble formation, than anything really.
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Re: Deep Safety stops

Postby Tony » Thu Jun 18, 2009 12:00 am

Don't always do deep stops, but like to make a nice slow ascent and if I'm close to deco etc then I will do a deep stop for 1min at approx 15m. I can see the point in doing deep stops especially seeing as its my safety that I am helping by doing them. I do however always do the safety at 5m.
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Re: Deep Safety stops

Postby Andy » Mon Jun 22, 2009 11:30 am

Azza wrote:The idea of the deep stops is more to slow your ascent, and limit bubble formation, than anything really.


Nicely said. In terms of non-deco dives, it's entirely arguable as to whether a stop at 5m has any benefit in terms of decreasing the risk of DCI. It's my personal opinion that the realy benefit of the 5m stop is that it's a pause that allows a diver to get control of their ascent for the last 5m rather than actually limit DCI.

What a 5m stop does is "potentially" reduce the impact of bubbles that have been formed in the bloostream, whereas a deeper stop eliminates bubble formation in the first place (alledgedly).

Both my Vytec and my VR3 essentially use the same algorithm, a 2 minute Pyle stop at approx half the maximum depth of the dive. Neither require a 5m stop, though like Azza I tend to do one as a matter of course. In fact, I tend to multiple deep stops when I can.

So for a 40m dive, my first stop would be 2 minutes at 20m. I'd then do 2 minutes at 10m and finally a 5m stop - recently, in the last year or so, I've reduced my ascent rate in the last 10m or so to a maximum of 3m/min. At places like the PKs, it's not like you're just hanging out doing nothing on the stops! Since I started graduating my ascents in this way, I've certainly felt a lot less fatigued after dives. It might be some empirical evidence showing reduced decompression stress, or it could be utter placebo effect and hogswash..... but it works for me.
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Re: Deep Safety stops

Postby SpaceMonkey » Mon Dec 21, 2009 3:52 pm

aquakiwi wrote:I'm not really familiar with them but understand they can be beneficial, at what depth? and can they take the place of the 5m stop.


I'd certainly never let them take the place of the 5m stop, although they certainly may be beneficial in addition to it. Remember your biggest change in pressure gradient (and therefore lung/BCD volume) takes place in that top 10 metres (the pressure halves from 2ATM to 1ATM), so it's always a good idea to take it easy to avoid runaway ascents or LEIs.
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Re: Deep Safety stops

Postby ChuckyBob » Mon Dec 21, 2009 4:41 pm

I guess it all comes down to the conditions but I have skipped many safety stops over the years mainly dues to either surge or high current.

As for doing deeper stops then once again it comes down to the conditions and the dive profile. For example if I did a no deco dive to 30-40 meters and there was lots of surface current but a nice reef I could hold onto at 10 meters then I would probably do a 3 minute stop there and skip the 5 meter stop. Any deeper than that and you risk on gassing more than off gassing.
But if the dive was only to 20 meters max and the rest of the dive was 10-15 meters then another 3 minutes at 10 meters probably wouldnt offer much benefit.

Decompression dives are a bit different. The shallower stops are probably much more important and deep stops are more of a normal dive profile.
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Re: Deep Safety stops

Postby aquakiwi » Mon Dec 21, 2009 6:04 pm

Thats pretty much what I wanted to hear, frequently conditions make the 3m stop uncomfortable.
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Re: Deep Safety stops

Postby Andy » Mon Dec 21, 2009 9:36 pm

ChuckyBob wrote:Decompression dives are a bit different. The shallower stops are probably much more important and deep stops are more of a normal dive profile.


What are you comparing here, Greg? Are you saying that shallow stops on a deco dive are more important than shallow stops on a non-deco dive, or that shallow stops on a deco dive are more important than deep stops on a deco dive?

The latter is certainly questionable. If I had to blow deco stops, I'd much rather blow shallow stops than deep. On the shallow stops, it's the slower tissues that are off-gassing where as the deeper stops it's the fast ones (brain, spine etc). It does depend on what you define as "deep" as well, for the sake of this I assuming "deeper" rather than "deep" and that the stops are mandated by the profile, not "added in" as a bubble reduction measure.

Of course, I'd much rather not blow any stops at all....

Whilst you can only generalise to a certain degree, and there will always be exceptions, missing deeper stops is more likely to lead to a Type II DCS whereas missing shallow is more likely to lead to Type I.
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Re: Deep Safety stops

Postby Andy » Mon Dec 21, 2009 9:48 pm

aquakiwi wrote:Thats pretty much what I wanted to hear, frequently conditions make the 3m stop uncomfortable.


With most deco models, Alan, you're essentially off gassing above "about 13m". The rate you are off gassing is proportional to the pressure difference between the gas dissolved in your body and the ambient pressure.... so 3 minute stop at 10m will release some gas, but not as much as a 3 minute stop at 5m.
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