Deep stops for reccies

[richies]

Following this link...
http://www.divernet.com/news/stories/bends261003.shtml

brings up an interesting article about "deep" stops for recreational diving.  I think there's argument about whether deep stops themselves are what works or whether it's the fact that they slow the ascent rate that makes it work, but I wonder, what does anyone think of this?

cheers

R

[Dr Stevil]

well, if "deep" is 15 metres as indicated by the article, then I'm regularly doing "deep" stops, if I've gone past 25m I'll spend about a minute at 18, 15, 12,  9 & 6, and probably kill some time at 3m if there's little or no swell, "what's the rush to get out" is my way of looking at things.

Is that being overly cautious ? Probably, but the TDI Deco Proc course made a deep and long lasting impression on my way of diving.
Chee-az
steve

[peter k]

I've been doing them since I got back in t'water. If I do a 30mtr dive then I'll stop at 20, 13, 9 + 5. If I hadn't listened to my D.O when I brought the subject up with him 1 1/2 ago then I might not have got bent. I was told this would only aggrevate the micro-bubbles when I told him I was going to start doing deep stops. I decided that, being the D.O., he knew better. My, how times change. Thing is he was a better D.O than the clueless wonder that's there now.  

Peter

[richies]

Ok, so what calculations do you use to do them?  

I usually spend 3 minutes at 6 and 3 minutes at 3 regardless (I do no-deco, above 30m), because there is no rush to leave, and I like floating and relaxing.

But I've been reading up on these stops and there are a number of ways of thinking about it.

One is, simply do a 1 minute stop at half your max depth, then do your regular stop/s.  I think this is recommended by NAUI or something similar.

Another is to start at 80% of your max depth, then if you're more than 10m from your first "necessary" (ahem) stop, do another minute at half the distance to go.  And so on.

You seem to do a stop every 3m or so, about a third of the way up from your max depth.

What are the reasons for doing it the way you do?

cheers

R

[Spike Jackson]

I think deep stops are a good idea and I tend to do short (30 secs - 1min) stops at 12 and 9 m on the way to my deco stops, in addition to doing a very gentle ascent. This is for "recreational" decompression diving requiring only a 6m stop.
However, I do think that to much of a good thing might turn out to be a bad thing, ie excessive unneeded deep stops could give extra ongassing of your slow tissue compartments?
Don't know enough about it!

[Dr Stevil]

Originally Posted by [b

Quote[/b] (spike jackson @ Oct. 29 2003,14:39)]However, I do think that to much of a good thing might turn out to be a bad thing, ie excessive unneeded deep stops could give extra ongassing of your slow tissue compartments?
Don't know enough about it!

Under some circumstances, possibly, but as stated by richies, off-gassing starts at 80% of your max depth, so all you're doing by including stops at  79%+ of max depth is, using the famous analogy, slowing down the unscrewing of the cola bottletop. Plus above 6 metres ongassing would be considered negligible so time spent at 6, 5 or 3  doesn't count for all practical on-gassing purposes.

[peter k]

Hi richie,
             At 80% you're borderline as to whether you're still on-gassing or off-gassing. 80% is the usual area where this changes from compression the decompression. I'll normally 1/3 my current dive depth and do 1min stop there. So from 45 mtrs bottom depth I'll come up like this-
45-30@10mtrs/min
Stop 1min@30
30-20@5mtrs/min
Stop 1min@20
20-13@3mtrs/min
Stop 1min@13
13-9@3mtrs/min
Stop 1min@9
9-5@1-3mtrs/min
Stop for as long as I can stand the cold/air lasts
3-5mins to surface.

So all my stops are at 45-30-20-13-9-5, with the ascent rates slowing down as I get nearer the surface. The first ascent is the quickest as this gets me out of the "zone" that I'm still compressing. It also takes care of those pesky little micro-bubbles better as you're giving them a chance to off-gas before they start growing into a problem. It only works out at an 8min ascent as compared to a standard 10mtr/min ascent that would take 5mins anyway. There's no great shakes in spending an extra 3mins coming up from depth really, in fact, it's bloody sensible.

Peter

[Ben Harris]

<font color='#8D38C9'>Theres a discussion on decobar about this, most seemed to think pyle stops in non deco dives was pointless unless it caused people to ascend slowly.
Personally cant see why putting in extra stops and pyle stops isnt a good idea as long as its done properely based on the ata of the dives. Most computers count deep stops as ongassing so might not make your computer happy.

[Mark Chase]

Hang on chaps we are all getting a bit carried away here.

Deep stops are for deco dives

Doing a deep stop on a non-deco dive and using back gas is not a deco stop. Its an on gassing stop. You dont just bung in deep stops for the hell of it. If you do then expect to get bent unless you have planned them into you’re profile or are following a computer. &nbsp;

Also if you plan dives on a soft where package you will soon notice that from 30m to 60m the first proper stop is usually at 18-24m That is to say a stop longer than 1min. This is because a deep stop below the low M value is detrimental to your profile. So if your doing a 30m dive the low M value is at 21m first proper deco stop is 15m for 3min.

So to plan a deep stop for a 30m dive you would first have to determine the low M value. Having determined it is 21m. You would ascend smartish to 21m say @ 10m/min and then do 3m/min ascent to first proper stop at 15m

This is all well and good but remember that all the time at depth is adding to deco unless you are gas switching so expect the time to surface indicator on your computer to rise and not fall if your doing back gas deep stops. (Unless you have a VR3 )

As an example I did a 40m dive in Gozo on air for 20mins. I left the bottom with 13mins of deco but 6mins later when I got to 9m I still had 13mins of deco. This was because I did not ascend immediately to my indicated deco ceiling of 3m but instead did a slow ascent and added 9m stops to the profile.

In total by the time I had completed deco I had done 20mins since leaving the bottom. That’s fine if you’re expecting it but not if you left the bottom on 50bar.

When Richard Pyle came up with deep stops he was using Bhulman tables that indicated first stop depths after a 60m dive on air for 30mins as 18m with an ascent rate of 18m/min. He then took the 18m stop as his base line to calculate the deep stops. On a no deco profile your first stop depth is sitting on the boat so 6m is a deep stop &nbsp;

Personally if you want to improve your off gassing on a no deco dive to 30m I would cut the base ascent rate down to 10m/ min to 15m then opt for 3m/min to 6m and 1.5m/min to the surface.

Dont bother stopping at all

ATB

Mark Chase

[Spike Jackson]

From my admittedly limited knowledge of decompression theory I'm inclined to agree with Mark Chase here. On a standard 30m no deco dive your fast tissues will saturate (ie blood and brain) but your diffusion limited tissues such as joint and fat are still playing catch up. So random deep stops may allow some offgassing of your fast tissues to occur (which will be taken care of anyway in your slow ascent) but will cause more ongassing of your slow tissues, which in turn need even longer to offgas.
To just chuck in deep stops on every dive is not a good idea in my mind, especially below 12m. Rather use a controlled ascent rate to allow for offgassing.