PADI Deco.....

[ScubaFeenD]

I believe you were talking about the recommended safety stops. These are simply performed to add an extra margin of conservatism to an already safe situation. PADI teaches that recreational divers should not be putting themselves in a position where they need to do deco stops. They consider deco diving to be out of the realm of recreational diving, it is technical diving.

That having been said, doing repetitive stops at depth will add to the nitrogen loading that we are trying to limit, and doing repetitive stops near the surface would be unnecessary and ineffective.

I hope that helps. Please don't hesitate to ask any follow up questions. It can be hard to be eloquent over the computer, but I will do all I can to help answer your questions.

Aren't all dives decompression dives?

You're not being that harsh really, I know what you mean. I basically concerned with eliminating as much gas as possible so there will be little to no risk of DCI after the completion of the dive or subsequent dives. I've been reading about the use of half stops/deep stops for a few minutes as a safety precaution and I was wondering whether or not it had any merit within rec diving.

Doing a safety stop is pretty much standard in my book. But I think if you want to efficiently off-gas you can be more proactive with an ascent profile where you stop at half your max depth for a minute, then a minute every 10fsw until you get to 15ft for a 3 minute safety stop. It's a more gradual ascent, and requires a bit more time, but is safer in my opinion.

I just don't understand how going from max depth to 15ft and then hanging there is considered OK. And I don't understand why more agencies don't teach better ascent control from the get go.

 

[Diver0001]

You're not being that harsh really, I know what you mean. I basically concerned with eliminating as much gas as possible so there will be little to no risk of DCI after the completion of the dive or subsequent dives. I've been reading about the use of half stops/deep stops for a few minutes as a safety precaution and I was wondering whether or not it had any merit within rec diving.

I see.

So what you're trying to say is that you've read about a number of other procedures and you'd like to know if they have any merit within the realm of recreational diving.

That's a lot different than coming out of the gate saying "PADI sucks".

But I think we're getting to the crux of it now.

Unfortunately, I have to give lessons in the morning and I need to go to bed.

I'll start this, though, by saying a couple of things:

- 18 m (60ft) per min, is generally thought to be too fast in this day and age.
- There is no limit to how long you can extend a stop at 6m (18ft) or less
- both reducing speed and extending the 6m stop are consistent with all agencies ascent protocols.
- the 1/2 depth thing probably won't help a whole lot in the domain of recreational diving but it probably won't hurt either.
- Learning how to make proper "stops" of no more than 1 min at 18/15/12/9 and 6 meters isn't a waste of time. It probably won't help you reduce your risk of DCS to make those stops, but making them will make you *aware* of things about your ascent that you probably aren't aware of now..... and it gives you control.
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

Bed time. Sorry. I think this discussion will get interesting now.

R..

 

[ScubaFeenD]

I see.

So what you're trying to say is that you've read about a number of other procedures and you'd like to know if they have any merit within the realm of recreational diving.

That's a lot different than coming out of the gate saying "PADI sucks".

But I think we're getting to the crux of it now.

Unfortunately, I have to give lessons in the morning and I need to go to bed.

I'll start this, though, by saying a couple of things:

- 18 m (60ft) per min, is generally thought to be too fast in this day and age.
- There is no limit to how long you can extend a stop at 6m (18ft) or less
- both reducing speed and extending the 6m stop are consistent with all agencies ascent protocols.
- the 1/2 depth thing probably won't help a whole lot in the domain of recreational diving but it probably won't hurt either.
- Learning how to make proper "stops" of no more than 1 min at 18/15/12/9 and 6 meters isn't a waste of time. It probably won't help you reduce your risk of DCS to make those stops, but making them will make you *aware* of things about your ascent that you probably aren't aware of now..... and it gives you control.
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

Bed time. Sorry. I think this discussion will get interesting now.

R..

I have no hard science to support what I am about to say, but I have nothing to completely refute it either.

I do the slow multilevel type ascent to help control bubble formation and to help make sure I control my ascent and can watch my depth gauge. More control and slower (without being too slow and on-gassing again) helps me, at least, psychologically. I suppose this wont change until I take a class that addresses it more completely, there is research to refute it/support something else, or until I read deco for divers, which might give me more insight.

Sleep well, I await your comments :-D

 

[ColinCB]

I see.

So what you're trying to say is that you've read about a number of other procedures and you'd like to know if they have any merit within the realm of recreational diving.

That's a lot different than coming out of the gate saying "PADI sucks".

But I think we're getting to the crux of it now.

Unfortunately, I have to give lessons in the morning and I need to go to bed.

I'll start this, though, by saying a couple of things:

- 18 m (60ft) per min, is generally thought to be too fast in this day and age.
- There is no limit to how long you can extend a stop at 6m (18ft) or less
- both reducing speed and extending the 6m stop are consistent with all agencies ascent protocols.
- the 1/2 depth thing probably won't help a whole lot in the domain of recreational diving but it probably won't hurt either.
- Learning how to make proper "stops" of no more than 1 min at 18/15/12/9 and 6 meters isn't a waste of time. It probably won't help you reduce your risk of DCS to make those stops, but making them will make you *aware* of things about your ascent that you probably aren't aware of now..... and it gives you control.
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

Bed time. Sorry. I think this discussion will get interesting now.

R..

Why is it a max of 1 minute at those stops? I thought it could be anywhere from 1-3mins?

Could somebody explain this a bit more? \/
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

 

[ScubaFeenD]

Why is it a max of 1 minute at those stops? I thought it could be anywhere from 1-3mins?

Could somebody explain this a bit more? \/
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

I think it is because you begin to on-gas if you stay too long at even a shallower depth. All tissues take on gas at a different rate, so tissues that began off-gassing can start on-gassing again negating the ascent profile. In other words, its just like diving at a slightly shallower depth, not really like ascending.

 

[Bubbletrubble]

Why is it a max of 1 minute at those stops? I thought it could be anywhere from 1-3mins?

I think Diver0001 was just referring to how some technical divers (GUE, UTD) manage their ascents. In their profiles, they will often include 1 minute stops at 10 ft. intervals. In contrast, other divers may incorporate slightly longer stops (modified deep stop) at 1/2 max depth (or some variation on this theme) with shorter stops between the deep stop and the shallow stop (approx. 10 - 15 fsw).

For recreational divers, the optimal duration and depth of deep stops has not been worked out yet.

I like Diver0001's take on the value of being in total control of the ascent rate. A series of one-minute stops at specific depths demonstrates mastery of buoyancy control. That's a good thing...something that all divers should be able to do.

Could somebody explain this a bit more? \/
- if you decide to go for *really* slow and you're ascending at less than 3m/min then you need to add your ascent time up to 6m to your bottom time because you're really making a protracted multi-level dive.

At least one venous gas emboli study has revealed higher bubble scores in divers who ascend at a "too slow" rate.

It's entirely possible that optimal ascent rates could be different depending on a diver's current depth.

 

[ScubaFeenD]

I like Diver0001's take on the value of being in total control of the ascent rate. A series of one-minute stops at specific depths demonstrates mastery of buoyancy control. That's a good thing...something that all divers should be able to do.

True that. n00bs like me need all the help we can get to maintain good control on ascent while diving dry. Being strict with myself regarding depth changes help keep me very mindful the whole way up.

 

[DiveNav]

........ - 18 m (60ft) per min, is generally thought to be too fast in this day and age....

Correct. In fact, most of the dive computer manufacturers have some kind of variable ascent rate algorithm - from a simple 2 speeds (60ft/min and 30ft/min with change at 60ft) to complex ones (with lots of speeds / trigger points)

........the 1/2 depth thing probably won't help a whole lot in the domain of recreational diving but it probably won't hurt either.

Granted that our body is way more complex than the Buhlmann 's based model ..... the deep stop at 1/2 dept clearly help with the - so called - fast tissues. The counter indication of this approach is the increased saturation of the slow tissues.
To somehow minimize this secondary effect, some manufacturers have even more complex deep stop algorithms that calculate the deep stop depth based on your current nitrogen loading and dive profile.

In general ... slower you ascend and better is.

Alberto (aka eDiver)

 

[DiveNav]

...... At least one venous gas emboli study has revealed higher bubble scores in divers who ascend at a "too slow" rate.....

mmmhhh ... do You have the paper?
Or I could check with Karl.

Alberto (aka eDiver)

 

[Peter Guy]

OP -- Take the following for what it is worth (which probably ain't much). I am NOT a specialist in decompression practice nor theory nor did I stay at a Holiday Inn last night!

Yes, every dive is a "deco" dive in that every time you breathe compressed gas while underwater your body will absorb (on gas) some of that gas and it will have to "unabsorb" (off gas) it when you return to the surface. While in "PADI-Land" we like to talk about "no deco limits" we are really talking about "no stop limits" in that a direct ascent to the surface is always permitted. While you will do a little bit of off gassing during the ascent, the primary off gassing period is while you are on the surface breathing in that big air tank in the sky.

As Diver0001 discussed, learning to do stops during your ascent may well be a very good strategy to make sure you are doing a controlled, and slow, ascent which will give your tissues some more time to off gas prior to getting to the surface. In addition, learning to do the stops is just good practice in "watermanship" and buoyancy control (not to mention it can be great fun taking your time to look at the little things in the shallows).

In my ever, and always, humble opinion, you are making too much of this whole deco thing. It really "ain't rocket surgery" and just requires following some pretty simple rules. Go diving, have fun, and spend at least half of your dive above 60 feet -- you'll be fine!