deep stops

[markg]

yesterday i had a bit of a disagreement with my regional coach.
he was talking about deco stops( the usual 9 6 3 m) when i threw a spanner in his works and mentioned deep stops. several months ago i dived with a guy using a vr 3 and on a 48 ish metre dive we did a stop at about 24 mtrs and after the dive i felt a lot less knackered than usual(diving air). since then i usually stick in a deep stop and find it helps with lethargy post dive. well, when i said this to rc he wasn't a happy bunny at all mentioning all sorts of nasty possibilites but i can't see why. i dive my computer (aladin pro) and always do as it tells me so if i rack up more deco doing a deep stop so be it.
but he insisted that deep stops must be done at an exact depth and i really shouldn't be getting involved with these sort of things.
is he talking "dive god" bullshit or is he right?
i'm sure someone on here will tell me because i honestly don't know
thanks in advance
markg

[Odin]

Originally Posted by markg

is he talking "dive god" bullshit?

markg

YES!
Even the new Suunto is doing Deep Stops!
Sounds like he needs to read the uptodate info out there!
Paul
BS-AC SW Region

[chrisch]

Originally Posted by markg

but he insisted that deep stops must be done at an exact depth and i really shouldn't be getting involved with these sort of things.

markg

That was the point at which you should have put your coat on and gone for a pint. Odin is correct - its bullshit.

The theory of deep stops is well know. Search YD for loads more or look at the theory on many agency websites. There is no exact depth. Mark - if you are smart enough to ask the question you are smart enough to "get involved". I would have told the guy he was a twat, but I am undiplomatic and rude...

It saddens me that people who clearly don't know shit feel the need to stop other people from adding to their knowledge because they fear looking less expert than they like to think they are. There's always someone who knows more than you - if you meet someone who does listen to them, argue if you like, but be prepared to think about the subject. If you don't you are a dinosaur, stuck in time for ever. I give lots of business presentations and nearly always learn something in the Q&A, or am provoked into more research, from which I learn....

Stick to YD mate.

Chris

[NotDeadYet]

Originally Posted by markg

well, when i said this to rc he wasn't a happy bunny at all mentioning all sorts of nasty possibilites but i can't see why

Let's face it, the BSAC 88 tables were out of date in 88 never mind today, so its hardly surprising that you got that reaction.

If you account for the stop in the profile then why should it make any difference. On a computer especially. It's no different from doing a multi-level dive with a very short level.

The question is what depth? Doing a stop at a random depth shouldn't have any ill effects provided the above applies. But it may not however have any positive effects either. You could do worse than follow Rich Pyle's advice of halfway between the bottom and the first deco stop/surface. Or start using a computer/tables that do it automatically.

[Helen F H]

Originally Posted by NotDeadYet

You could do worse than follow Rich Pyle's advice of halfway between the bottom and the first deco stop/surface. .

I would reccomend Pyle stops too. I saw a presentation on them at the dive show in london - damned good idea.

[Woz]

OK half way but how long for?

[turbanator]

Originally Posted by Woz

How long for?

2 Mins minimum.
Pyle is an icthyologist (sp?) and when he collects specimens from depth he has to stop and remove air from their swim bladders with a hypo.

He noticed that he felt better after dives when he caught fish than when not, so put the stops in on all dives.

Conventional wisdom suggests 2mins as that is the time for the blodd to make a complete circuit of the body.

r
Paul

[chrisch]

Originally Posted by turbanator

Conventional wisdom suggests 2mins as that is the time for the blodd to make a complete circuit of the body.

A very slow swimming fish, the blodd....

Chris.

(Yes a couple of minutes is the generally agreed time).

[Mark Powell]

Most modern deco approaches include some form of deep stop. Suunto and Uwatec are starting to introduce them into their dive computers. Many agencies are also accepting that they are a good thing and DAN recently published some research in support of deep stops.

Pyle stops are the easiest way to incorporate deep stops into your diving.

1) Calculate a decompression profile for the dive you wish to do, using whatever software you normally use.

2) Take the distance between the bottom portion of the dive (at the time you begin your ascent) and the first "required" decompression stop, and find the midpoint. You can use the ambient pressure midpoint if you want, but for most dives in the "technical" diving range, the linear distance midpoint will be close enough and is easier to calculate. This depth will be your first deep safety stop, and the stop should be about 2-3 minutes in duration.

3) Re-calculate the decompression profile by including the deep safety stop in the profile (most software will allow for multi-level profile calculations).

4) If the distance between your first deep safety stop and your first "required" stop is greater than 10 m, then add a second deep safety stop at the midpoint between the first deep safety stop and the first required stop.

5) Repeat as necessary until there is less than 10 m between your last deep safety stop and the first required safety stop.

For a good explanation of why deep stops are a good things then take a look at the following link.

http://www.dive-tech.co.uk/resources/deepstops.pdf

and if you want to find out more about decompression theory (or send along your regional coach) then you might want to take a look at the following post.

http://www.yorkshire-divers.co.uk/fo...ad.php?t=11094

[Mark Powell]

Research by Divers Alert Network (DAN) has shown that carrying out an initial stop at a considerably greater depth than the traditional decompression profiles recommend, provokes less bubble formation in the bloodstream of recreational divers.

Researchers measured the bubbles formed* in the bloodstream of ascending divers who had carried out identical repetitive dives to 25 metres on air. The divers carried out 3 different ascent rates of 3m, 10m and 18m per minute. These ascent rates were combined with different ascent profiles:
- the first being no stops,
- the second involved carrying out the traditional safety stop at 6 metres,
- the third profile involved carrying out a 'deep stop' at 15 metres, followed by a stop at 6m.

None of the divers involved in the research developed decompression illness. The divers who performed no stops on their ascent had the greatest number of bubbles in their bloodstream, scoring highest on the Doppler Bubble Score Index, and the divers carrying out an ascent rate of 10m per minute and making stops at 15m and 6m had the least.

"The introduction of a deep stop appeared to significantly decrease Doppler recorded bubbles and gas tension loading in the fast tissues [of the body]" according to Dr Frans J. Cronje and Professor Alessandro Marroni.

The research provides the first scientifically significant study to support the practice of deep stops for recreational divers, and is reported in the DAN journal Alert Diver. Previous research, carried out on mixed gas divers, proved inconclusive.

Deep stops, popularised by Richard Pyle, are a subject of debate among technical divers who are carrying out dives that require a substantial amount of decompression time in-water. Most technical diving profiles now include deep stops, carried out at a depth which is more than half the maximum depth reached on the dive.

*Bubble formation is measured by 'listening' for bubbles passing across the right ventricle of the heart using ultrasound. The technique is known as Doppler Bubble Score Index, and the larger the number of bubbles detected, the higher the Doppler BSI. Higher Doppler BSI's are associated with a greater probability of developing decompression sickness.