Safety stops

[Dan12706]

Awhile back I read about a different type of safety stop. Instead of 3 minutes at 15-20ft etc. they were talking about multiple stops based on depth of dive ie: if a 80 ft dive you would stop at 40ft for one minute, 20ft for one minute, 10ft for one minute etc.. I have seen 2 articles that were unclear to me, then no news at all does anyone have any further info/advice ? Dan

 

[mania]

As far as I understand it - what you are talking about are two different things. Safety stop is a stop that should be done at the end of dive at the depth of 5 - 3 meters for 3-5 minutes. Multiple stops are called "deep stops" and some time ago were limited to technical diving (it includes change of gases) while now are also recommended for recreational divers. So to make a long story short - especially that I'm not an expert on that - according to nowadays theory every dive is a decompression one so deep stops are in fact a decompression procedure.

Few years ago - and still most of the agencies teach this way - it was told that there are no deco dives and decompression dives. For no deco ones safety stop was enough to desaturate inert gas. But as I wrote before - and for me it's simply logical - there is no such thing as no deco dives. In that case you need more time to desaturate hence the deep stops. Anyway the last deep stop is done for 3 minutes.

You can read about deep stops here:
http://www.wkpp.org/articles/Decompression/first_deep_stops.htm

As I said - I'm not an expert on that and I do know that here are real experts so I'm sure they can explain it much, much better that I did (and correct my mistakes). I had the deep stop theory during my nitrox course but as a Master of Literature I had to reason them to be able to understand without all this physics (gee I always hated it). So all I wrote is how my mind - a humanistic one - understands it.

Mania

 

[sharkbaitDAN]

What I think you are talking about are just deeper safety stops, but with a complete 3-5 minute safety stop as usual at 10-20 feet. Stopping at intermediate depths for a minute or two mostly increases off gassing time under pressure; in other words it slows the ascent. There are not any rules that I am aware of regarding deeper stops in no-decompression diving. I generally stop for a minute or two at half-depths. On a 100' dive, 1 minute at 50' or 60', then 2 minutes at 30'. and a 3 minute stop at 15'. On a 60' dive, I would do a minute at 30' and then a 3 minute safety stop. This is just to add a margin of safety to dives when I am using a computer. Based on tissue loading that I get off of it after the dive, it seems that I have less gas in my system after doing the deeper stops. There is some data out there that seems to back this up, not sure where it is.

 

[jiveturkey]

If you do a search under "deep stops" you'll find all kinds of discussion.

 

[jonnythan]

IMO, the idea is to progressively slow your ascent as you get shallower. A "deep stop" may or may not be good, depending on your nitrogen loading and I don't think it's a good idea to just guess. If you keep your ascent slow, take a 1 minute stop at 30 and 20, then slowly go up to 10 and take a 2 minute stop, then ascend the rest of the way as slowly as possible, I think you're doing all you can.

 

[Soggy]

I don't know how other agencies teach it, but GUE teaches a 'minimum deco' ascent which includes on ALL dives 1 minute at 30', 20', and 10'. Additionally, deep stops are started at 80% of your max atmospheres or 75% of your maximum depth (they come out to be about the same number) and continued every 10' thereafter.

So, for a 100 foot dive, the stops would be
70' - :01
60' - :01
50' - :01
40' - :01
30' - :01
20' - :01
10' - :01

This has the effect of slowing the ascent to 10 ft/min after the first deep stop and also beginning offgassing of certain tissues earlier. It only makes sense...if you spent your entire dive at 100', why would you only stop at 15' for 3 minutes? That's a difference of 2.5 atmospheres, or about equivalent to doing a 85 foot dive and just doing your 'safety stop' on the surface.

 

[kalvyn]

Awhile back I read about a different type of safety stop. Instead of 3 minutes at 15-20ft etc. they were talking about multiple stops based on depth of dive ie: if a 80 ft dive you would stop at 40ft for one minute, 20ft for one minute, 10ft for one minute etc.. I have seen 2 articles that were unclear to me, then no news at all does anyone have any further info/advice ? Dan

Others have already covered the GUE angle on deep stops and ascent profiles, so I'll skip that.

NAUI recently (last year?) came out with and is now teaching to their Open Water students the "Rule of Halves". This is a stop at one-half your max depth for one minute, then a two minute stop at 15'.

I learned the GUE method and that's what I do when I dive. The NAUI "Rule of Halves" is definitely a good change in the right direction with regards to "safety stops", in my opinion. I was glad to see a major training agency ackowledge and incorporate the concept of deep stops.

Jimmie

 

[StSomewhere]

So, for a 100 foot dive, the stops would be
70' - :01
60' - :01
50' - :01
40' - :01
30' - :01
20' - :01
10' - :01

This has the effect of slowing the ascent to 10 ft/min after the first deep stop and also beginning offgassing of certain tissues earlier. It only makes sense...if you spent your entire dive at 100', why would you only stop at 15' for 3 minutes? That's a difference of 2.5 atmospheres, or about equivalent to doing a 85 foot dive and just doing your 'safety stop' on the surface.

I *get* this, but don't you have to account for some on-gassing at the deeper stops? Obviously less you would at max depth, but still some amount? Or does the slower ascent rate of 10 ft./min than the "normal" (whatever normal is) account for that?

 

[jonnythan]

Yeah, that's what I wonder about Soggy's example. If it was a short dive you could easily still be taking on gas at a deep stop like that (I would think). I'm not sure what I think of that but I would appreciate if someone versed in the subject spoke up.

 

[novadiver]

It's a dive phisics thing, It has it's roots in the slow release of presure vs. time and depth. If you do the math on any dive profile and then add a deep stop you'll see a change in the average depth, this lets the body offgas before the bubble shower begins.

Soggy's profile is a good one because it also give a diver up to 40 min of BT and still be concidered a no deco dive.( with the right mix)