Safety Stop/ Minimum Deco

[FireInMyBones]

As I continue to grow into a more experienced diver, I wish to be as safe as possible on my ascents.
[sm]After talking to my wife and looking at our budget, Fundamentals is out for this year (unless I can find the money some other way than my current jobs).[/sm]

I took the UTD Ratio Deco class and still want more information on the Minimum deco stops, as I feel I would get more from talking to someone about it all.

I keep hearing about 30 second holds and 30 second slides. I think I understand the concept: hold a depth for 30 seconds and take 30 seconds to "slide" to the next depth (10' less). It is the start depth I have the question about. The traditional "safety stop" is at 15' (best I can tell) and I start my hang on O₂ at 20 if I am doing a deco stop.

I am sure that this all sounds rather convoluted, but I am genuinely curious on the matter. Could someone please explain?

 

[vjanelle]

TL;DR: You start at 50% of your max depth, unless you're comfortable with the techniques behind depth averaging.

The traditional DSAT recreational safety stop was meant to slow down the average ascent rate of your average recreational diver that's ascending to the surface without stop. Hence the convoluted rules on the back of the card:

"A safety stop for 3 minutes at 15' is required any time the diver comes up to or within 3 pressure groups of a no-decompression limit and for any dive to a depth of 100' or greater"

All diving is decompression diving, it just depends on how much time you have to spend decompressing, with min deco the time spent ascending(after a 50% deep stop) and holding at 1 minute every 10' will allow your body to offgas its fast tissues without the need of 'bending and mending' so to speak at 15'.

On a side note, O2 is for accelerating decompression, you shouldn't really be switching to a rich mix unless you have a need for it.

 

[TSandM]

Basically, the idea is to slow your ascent rate to 10 fpm from half of your average depth for the dive (or deeper, if you need to weight the dive for sawtooth profiles or other reasons). You can do that by using 30 seconds to ascend 10 feet, and then hold for 30 seconds at the stop depth. (That's the 30 second "slide", and 30 second "hold" idea.) Sometimes we'll extend the "shallow stops" (30 feet and up) if, for example, we've done several dives that day.

 

[rjack321]

I keep hearing about 30 second holds and 30 second slides. I think I understand the concept: hold a depth for 30 seconds and take 30 seconds to "slide" to the next depth (10' less). It is the start depth I have the question about. The traditional "safety stop" is at 15' (best I can tell) and I start my hang on O₂ at 20 if I am doing a deco stop.

I am sure that this all sounds rather convoluted, but I am genuinely curious on the matter. Could someone please explain?

The "traditional" safety stop involves a 60fpm race up to 15ft then a 3 min hang before doing a 45fpm ascent to the surface (seriously most divers finish the stop and literally pop to the surface afterwards)

This has changed in some agencies to 30fpm up to 15ft for 3mins.

We basically take that 3mins+ and spread it out between roughly 50% of the depth and the surface. 30fpm up to 1/2 the depth then 1min per 10ft above that. Call it 30sec slides, 30sec stops. Or 1 min stops running together. However you describe it in practice its 10fpm from 50% depth up. Which is almost always as long or longer than a traditional 3mins at 15ft.

Conceptually a long shallow stop addresses slow compartments (tissues) yet on a short recreational dive "fast and pretty fast" tissues are really the controlling tissues. Slowing the ascent earlier allows these tissues (conceptually) to offgas without forming a bubble. Once formed bubbles are not easy to drive back into solution and then offgas.

Reality is that controlled 10fpm ascents are just good habits for all kinds of diving and the race up to 15ft and stop habit doesn't really work in deco/cave dive plans. Where you do the time (within reason) is less important than having "enough" minutes between the bottom and the surface, typically 3 to 6 mins in recreational dives.

 

[FireInMyBones]

You start at 50% of your max depth, unless you're comfortable with the techniques behind depth averaging.

I got that from the class, and I am familiar with depth averaging to some degree. I just need more practice.

All diving is decompression diving, it just depends on how much time you have to spend decompressing...

That idea rocked my world in my Decompression Procedures class two years ago.

On a side note, O2 is for accelerating decompression, you shouldn't really be switching to a rich mix unless you have a need for it.

I only take what I need for a dive. If I am doing deco, I take the O₂.

 

[divad]

I got that from the class, and I am familiar with depth averaging to some degree. I just need more practice.

I'd love to practice with someone beside myself if you're interested.