Deep Stops

[Geoff Oldfield]

I've met a few divers now that have suffered repeated "mild" skin bends. Some of which have been treated with hyperbaric recompression and some by simply admionistering 100% O2 on demand until all apparent symptoms have disappeared. Naturally they all continue to dive, but now advocate deep stops, sometimes including Nitrox.

Does the BSAC or anyone else for that matter have any information to support the theory of deep stops after deep dives. As to me, it makes perfect sense to carry out stops starting at half the depth between the deepest depth and the first recommended stop. This would allow micro bubbles to dissipate before their growth is accelerated by the increased pressure gradient on rising directly from depth to the first recommended stop.

Any info would be greatly appreciated

Thanks

Geoff

[stu]

I've met a few divers now that have suffered repeated "mild" skin bends. Some of which have been treated with hyperbaric recompression and some by simply admionistering 100% O2 on demand until all apparent symptoms have disappeared. Naturally they all continue to dive, but now advocate deep stops, sometimes including Nitrox.

Does the BSAC or anyone else for that matter have any information to support the theory of deep stops after deep dives. As to me, it makes perfect sense to carry out stops starting at half the depth between the deepest depth and the first recommended stop. This would allow micro bubbles to dissipate before their growth is accelerated by the increased pressure gradient on rising directly from depth to the first recommended stop.

Any info would be greatly appreciated

Thanks

Geoff

have a look at
<a href="http://www.bishopmuseum.org/research/treks/palautz97/deepstops.html" >http://www.bishopmuseum.org/research/treks/palautz97/deepstops.html</a>. The original pyle stops !!! also a few reference at the end of the article. I do deep stops when trimix diving, the last 60 meter dive I did the first stop was 38m and then 27 meters for 2 mins. Hope the article helps.

Stu

[nick kay]

Hi Geoff

1. BSAC ERD "sort of" teaches deep stops, i.e. you're taught to use (eg) ProPlanner (or similar). If you set the MicroBub option you automatically get deep stops.
2. TDI Trimix actively teaches deep stops
3. Since doing ERD, my buddy and I carry out deep stops - even on (longish) dives in the 30-40m range. We both believe we feel better after the dive(s) by doing so
4. Have a look at the GAP website ( <a href="http://www.gap-software.com/" >http://www.gap-software.com/</a>) you can download a number of papers from there dealing with theory of deco, deep stops, etc.

[Geoff Oldfield]

Thanks Stu & Nick, something to be having a good look at methinks!

Regards

Geoff

[Paul Oliver]

Geoff

These were covered a while ago on YD, Peter K and a few others came out with some very good stuff / links and sold me. I tend to use the 2/3 method now (as recomended by Peters Hyperbaric Doc)and that with the very slow assents my branch has always used seems to work well. My SUUNTO eather likes them or is totally confused.

Regards

Paul

[Geoff Oldfield]

Thanks Paul, I remember now, there was something on the YD site a little while ago. I'll go back and have a trawl. Thanks

Geoff

[nick kay]

1. What's YD?
2. 2/3 method - where can you get info on this
3. Slow ascents? What do you class as "slow", BSAC ERD and TDI Trimix is based on achieving & maintaining 10m/min

[john kendall]

3. Slow ascents? What do you class as "slow", BSAC ERD and TDI Trimix is based on achieving & maintaining 10m/min

Um, Only at depth. what you want to achieve is a exponential ascent rate. Part of this is by adding stops, partly by slowing your ascents as you get shallower. (i.e 6mins from 6m to the surface)

Have a play with some software like GAP that gives you a graphical represenation of the dive. Set the Gradient factors to 20/80 and see what the output gives you.

HTH
John

[nick kay]

Um, Only at depth. what you want to achieve is a exponential ascent rate. Part of this is by adding stops, partly by slowing your ascents as you get shallower. (i.e 6mins from 6m to the surface)
Agreed - was referring to stops prior to 6m. In fact when I did ERD, an extra safety stop was invariably introduced at 3m followed (where conditions permitted) a 2min ascent from 3m!!

Have a play with some software like GAP that gives you a graphical represenation of the dive. Set the Gradient factors to 20/80 and see what the output gives you.
Have GAP, prefer it to ProPlanner for the simplicity of production of BailOut reports etc.
One problem I've found with GAP, is it that I'm not sure it calculates EAD/END correctly???

[john kendall]

:=Um, Only at depth. what you want to achieve is a exponential ascent rate. Part of this is by adding stops, partly by slowing your ascents as you get shallower. (i.e 6mins from 6m to the surface)
Agreed - was referring to stops prior to 6m. In fact when I did ERD, an extra safety stop was invariably introduced at 3m followed (where conditions permitted) a 2min ascent from 3m!!

:=Have a play with some software like GAP that gives you a graphical represenation of the dive. Set the Gradient factors to 20/80 and see what the output gives you.
Have GAP, prefer it to ProPlanner for the simplicity of production of BailOut reports etc.
One problem I've found with GAP, is it that I'm not sure it calculates EAD/END correctly???

Well you could always calculate it yourself. I don't know if GAP will do END with O2 as Narcotic, which might be where you get differences.

Can't actually comment on GAP much as I use Decoplanner

I also don't care too much about ENDs as I tend to use standard mixes, which have ENDs of less than 30m at the depths you use them.

Also, EAD and END are different things, EAD is used for calculating Decompression using Air tables, while diving Nitrox, END is used as a measure of Narcosis in Trimix.

John

[nick kay]

Well you could always calculate it yourself. I don't know if GAP will do END with O2 as Narcotic, which might be where you get differences.
&gt;&gt; Thats where the "problem" arose - calculated a Trimix dive using ProPlanner came up with a set of figures, fed them into GAP to get a (sanity check) comparison. Deco not dissimilar, but I thought I'd specified a 30m "head" - GAP said it was a 35m "head". Recalculated - still got "30m", went back to the TDI training manual, still got 30m...

Also, EAD and END are different things, EAD is used for calculating Decompression using Air tables, while diving Nitrox, END is used as a measure of Narcosis in Trimix.
&gt;&gt; Yes, my mistake - I should have just referred to
END

[beanie]

:=Well you could always calculate it yourself. I don't know if GAP will do END with O2 as Narcotic, which might be where you get differences.
&gt;&gt; Thats where the "problem" arose - calculated a Trimix dive using ProPlanner came up with a set of figures, fed them into GAP to get a (sanity check) comparison. Deco not dissimilar, but I thought I'd specified a 30m "head" - GAP said it was a 35m "head". Recalculated - still got "30m", went back to the TDI training manual, still got 30m...
turn O2 narcotic off

[nick kay]

turn O2 narcotic off
Thanks - kept missing that - found it in the end under (blatantly obvious) "Gas Settings"

[Chris Cherrington]

This has been an interesting thread - the so-called "Pyle" stops are pretty much well accepted I think. Re Trimix there is a need for deeper stops due to the He in the mix.
What are your views on the value of a stop at the gas switch stage on accelerated deco. For example switch to EAN50 at 20/18m but make this into a "stop" by a slow gas switch one buddy at a time??

[Beanie]

This has been an interesting thread - the so-called "Pyle" stops are pretty much well accepted I think. Re Trimix there is a need for deeper stops due to the He in the mix.
What are your views on the value of a stop at the gas switch stage on accelerated deco. For example switch to EAN50 at 20/18m but make this into a "stop" by a slow gas switch one buddy at a time??
eh what does this mean?
?????by a slow gas switch one buddy at a time???????

the rest of it I take is gas flushing ie extend you first stop on a gas to flush your system I believe 5 mins is the norm // required for this to be of use

[Chris Cherrington]

:=What are your views on the value of a stop at the gas switch stage on accelerated deco. For example switch to EAN50 at 20/18m but make this into a "stop" by a slow gas switch one buddy at a time??
eh what does this mean?
?????by a slow gas switch one buddy at a time???????

the rest of it I take is gas flushing ie extend you first stop on a gas to flush your system I believe 5 mins is the norm // required for this to be of use

Sorry - I didn't make this clear - I was thinking of Air to EAN50 not Trimix so the flushing would not really count as such (O2/N2 to O2/N2...)
I'll try again - with an air dive you can shorten deco by using a rich deco mixture. Typically this means a gas switch at the first stop. Stop deeper and switch at 20/18m (near the MOD for 50) instead.
Hope that's clearer.

[Beanie]

:=:=What are your views on the value of a stop at the gas switch stage on accelerated deco. For example switch to EAN50 at 20/18m but make this into a "stop" by a slow gas switch one buddy at a time??
:=eh what does this mean?
:=?????by a slow gas switch one buddy at a time???????
:=
:=the rest of it I take is gas flushing ie extend you first stop on a gas to flush your system I believe 5 mins is the norm // required for this to be of use

Sorry - I didn't make this clear - I was thinking of Air to EAN50 not Trimix so the flushing would not really count as such (O2/N2 to O2/N2...)
I'll try again - with an air dive you can shorten deco by using a rich deco mixture. Typically this means a gas switch at the first stop. Stop deeper and switch at 20/18m (near the MOD for 50) instead.
Hope that's clearer.

ah

yes same as what I meant flushing the N2 out not just the He (if present)
you should do the gas switch at its MOD anyway in addition to this you can saty at the swith depth for 5 mins which gives a higher pressure gradient to off gas (oxygen window effect - i think thats what they call it) GUE has some good article on this

[nick kay]

I'll try again - with an air dive you can shorten deco by using a rich deco mixture. Typically this means a gas switch at the first stop. Stop deeper and switch at 20/18m (near the MOD for 50) instead.

So for a (say) 40m dive you have a mandatory (say) 9m stop.
Elect for a deep stop at 25m on air for 1min
Then an 18m stop switching to 50% and do a 1 or 2min stop
Then your 9m stop remaining on 50%

If you dive using ProPlanner, it'll probably suggest a 12m stop in addition to the above.

FWIW (1), my buddy and I have been doing these stops for the past year. On occasions, one of us has 50% the other 70% - we do the same stops, one of us swapping at 18m/50%, the other swapping at 9m/70%. Yes, it'd be more sensible if we had the same gases, but if you last had a 70% fill its more economic to air top it and get a resulting 50% or thereabouts than go for an empty/fill

(2) Incidentally, we'll often do the dive profile described above, clear the Slate(s), then remain at 6m to clear the Nitrox (air integrated) computers and then (conditions permitting) go up to the 5m-3m range and clear the air (wrist) computers

(3) Theres also the case for saying... OK, if my first stop (voluntary or mandatory) is 24m, then I may aswell go for a 40% deco mix. That way you can get on at the 1st stop and remain on it until you're out of the water (plus breathe it in the boat for extra safety if you want to)

[Chris Cherrington]

=(3) Theres also the case for saying... OK, if my first stop (voluntary or mandatory) is 24m, then I may aswell go for a 40% deco mix. That way you can get on at the 1st stop and remain on it until you're out of the water (plus breathe it in the boat for extra safety if you want to)

Thanks guys - this makes sense to me. Beanie - I'll look at the GUE stuff, although I'm not sure what (HRH) Jarod would make of all the different gas mixes :-)

[Beanie]

=(3) Theres also the case for saying... OK, if my first stop (voluntary or mandatory) is 24m, then I may aswell go for a 40% deco mix. That way you can get on at the 1st stop and remain on it until you're out of the water (plus breathe it in the boat for extra safety if you want to)

Thanks guys - this makes sense to me. Beanie - I'll look at the GUE stuff, although I'm not sure what (HRH) Jarod would make of all the different gas mixes :-)

trick is to ignore the set gases and read the theory this is the one good thing to come out of there - everyone else was doing it anyway

[matt]

This has been an interesting thread - the so-called "Pyle" stops are pretty much well accepted I think. Re Trimix there is a need for deeper stops due to the He in the mix.

Have a look at the stuff coming out of DAN's Dive Explore and Safe Dive projects which are monitoring real world diving practices. The early indications are that deep stops are more important than ascent rates. Deep stops are not just for Trimix are not just for Trimix.

What are your views on the value of a stop at the gas switch stage on accelerated deco. For example switch to EAN50 at 20/18m but make this into a "stop" by a slow gas switch one buddy at a time??

I have been using deep stops in all my decompression dives for the last 6 years. I average avout 60 such dives a year. Typically these are dives in the 30 to 45m range with bottom times of 30 to 50 minutes. My technique has varied in response to reading stuff, hearing stuff and doing stuff. My current technique has been stable for a little over 2 years.

I refuse to use any table with BSAC written on it for decompression diving. My plans are based on Buhlmann tables and I use Proplanner to check the schedules.

I use the Pyle method of halfing the travel distance to the first shallow stop. Deep stop times are always two minutes. Ascent rate between deep stops is always 10m/min. The ascent rate between shallow stops (mandatory stops) is always 3m/min. The final shallow stop is always made between 4.5 and 5.5m depending on surface swell. I include a 3m, 3min safety stop on all dives.

The gas switch is made at the MOD of the deco gas. I use a deco MaxPPO of 1.6 (and don't give a fudge what BSAC happen to say). A 2 min stop is tacked onto the switch to extend the time breathing at Max PPO. The 2 mins starts after both divers have completed the gas switch.

I use Air for all dives shallower than 45m. I use 80% as a deco gas for all mandatory decompression dives. Generally you will see me carrying a deco stage on most dives deeper than 25 meters.

Air + accelerated deco on 80% gives similar ascent times to an optimised Nx mix without accelerated deco. It has the advantage of avoiding the hassle of having to know what your max depth is going to be on the day and is very cost effective in terms of gas fills.

Personally I do not accelerate deco on mixes &lt;70%. I have used 50% for accelerated deco in the past but had the same type of sub-clinical symptoms associated with using air. My explanation (no one elses) is that I feel a PPO &lt; 1bar is inadequate for accelerated deco. With a 50% mix the PPO drops below 1 bar shallower than 10m, the depth range which accounts for the bulk of your stops.

I played with gradient factors for a while but have since abandoned them. I feel the deep stops are not deep enough and the shallow stops are too long.

YMMV

Regards
Matt

[Mark Scott-Simons]

I played with gradient factors for a while but have since abandoned them. I feel the deep stops are not deep enough and the shallow stops are too long.

GFHigh &gt; 100%

Scotty

[matt]

:=I played with gradient factors for a while but have since abandoned them. I feel the deep stops are not deep enough and the shallow stops are too long.

GFHigh &gt; 100%

Sounds like your moving into guinea pig territory there.

IIRC 100% refers to the % of Buhlmann's M-Value that the model will permit. Setting GFHi &gt; 100% will allow a compartment to supersaturate above the limit which has been accepted as 'safe'.

Regards
Matt

[Mark Scott-Simons]

Sounds like your moving into guinea pig territory there.

IIRC 100% refers to the % of Buhlmann's M-Value that the model will permit. Setting GFHi &gt; 100% will allow a compartment to supersaturate above the limit which has been accepted as 'safe'.

True, but if you accept that the 'bend and mend' approach is wrong by adding deep stops then you don't need the over long shallow stops.

Scotty

[Vic]

&gt;&gt; GFHigh &gt; 100%
&gt;&gt;
&gt; Sounds like your moving into guinea pig territory there.

Not really. Many people do this (not me, I hasten to add - I'm a congenital coward). There's sufficient material published for it to be done in comparative safety.

&gt; IIRC 100% refers to the % of Buhlmann's M-Value that the
&gt; model will permit.

Not quite - that's that maximum over-pressure that Buhlmann's (final) published criteria will permit; the model allows you to do what you like with an M-value - it's just a parameter.

IIRC, Buhlmann's original derived values were very much higher than those currently used. He modified them because his test divers were getting bent; there's no magical property about the numbers he eventually chose, they're just the tool he used to control the DCS incidence. It is extremel;y likely that much of this incidence was down to the ascent procedure used which, by "modern" criteria, was provocative.

By performing a less-provocative asscent, then, it should be possible to allow a greater tissue saturation[1]. And the theory does seem to work...

&gt; Setting GFHi &gt; 100% will allow a compartment to
&gt; supersaturate above the limit which has been accepted
&gt; as 'safe'.

The difference, really, being that the "safe" level was only derived by provocative testing. Consideration of any instantaneous level as "safe" implies the use of a saturation-only model; as soon as we introduce any sort of bubble model, then it is bubble size that defines what is "safe", with tissue saturation being merely one factor that influences bubble size.

And if we're doing saturation-only models, deep stops are evidently a waste of time... ;-)

Vic.


[1] Tissue saturation is, of course, a mathematical concept in this context, so it's not really worth thinking *too* hard about the underlying biology, which always turns out to be far more complex than we'd imagined anyway...

[Norm]

I agree with what you said. Deep stops cannot be argued, their track record speaks for itself, in my opinion. On another note, a good friend of mine had repeated skin bend incidences over a period of about two years. They appeared to worsen each time they occurred. Finally, he took a major CNS hit that nearly killed him. A year later he took another, similar but worse CNS hit. I wonder if repeated skin bends could be an indicator of deeper, underlying problems?