safety stop question

[rossh]

Perhaps the most important aspect of recreational ascents, is to "get off the bottom" and get moving up. This prevents any further on gassing. After about half way up the ascent, just about any ascent type will work.

Which is more successful? That's hard to measure. Listening to bubble sounding scores is of little value, as bubble counting is NOT a measure of potential injury state. The medical system measures success by injury rate - which is very unlikely here. Divers want to measure success by feelings of wellness, satisfaction and after dive happiness - subjective expressions that the medical system will ignore.

Regards

 

[TSandM]

boulderjohn, the problem with the Marroni studies was that they ran the same ascent rate from the bottom to the surface. A 10 fpm ascent from 70 feet is definitely not the best profile -- as Ross says, you have to get OFF the bottom. Marroni did not look at the ascent type described here, with a rapid move up to 1/2 max depth, and then a slow ascent in the shallows. And, also as Ross says, bubbles don't equal DCS, or even the subjective measures of what may be "decompression stress".

 

[BluewaterSail]

Arrgh. To cut through all the dancing around, what the OP is describing is "Min Deco". Because of it's association with early GUE, AG, and now UTD, it often gets lumped in with common hostility toward DIR and "those people". There are many subtle variations of Min Deco, as can be found with a simple Google search.

I was wondering how long it would take someone to mention GUE.

One explanation that I have read for the GUE Minimum Deco is that it is just a tool to do a slow ascent. By breaking each 3 meters into 30 second hold and 30 seconds slide to the next depth, you are actually just doing a slow ascent in bite sized, easy to handle and control chunks.

To me there is a major philosophical difference with mainstream. As with everything in the DIR world, its part of a system, and hard to separate it from that. Mainstream safety stops are generally considered "optional"; to GUE divers, all dives are decompression dives, and hence "minimum decompression", and an MDL rather than an NDL. An extra ounce of safety precaution.

Of course that doesn't stop anyone from borrowing from there the bit that interests them.

 

[TSandM]

Bluewatersail, may I correct your post just a bit? All dives ARE decompression dives. ALL dives involve the absorption of nitrogen at depth, and require that that nitrogen be expelled from the body, which is what decompression is. Although the essence of recreational diving is that the surface is always an option, remember that that ascent to the surface is to be accomplished at a specified rate, and no faster -- which means you are, in a way, ensuring a certain amount of decompression time before surfacing. The only difference between that and diving the Doria is that, on the deep dive, the required time which has to pass before you can surface is so great that it has to be broken into stops, which are accomplished at specific depths.

What minimum deco does is slow the ascent rate from a dive from 60 or 30 fpm, to 10 fpm in the shallow section of the ascent (above half the maximum depth). I do not know that there are any objective data to show that this is preferable to the 30 fpm ascent to a 3 minute 15 foot safety stop, but I do believe there are data that a brief (2 - 3 minute) stop AT the half maximum depth results in lower bubble grades, which is why NAUI decided to recommend this strategy.

If we understood DCS better from a physiological standpoint, we'd have a better idea of how to structure perfect ascents, to drop the DCS rate to zero. Unfortunately, we just don't know enough about the condition to do that. There are a variety of approaches to ascents, and it's almost impossible to prove one superior to another when the rate of DCS in recreational dives (executed within no-deco limits) is so low.

 

[vladimir]

.....

 

[boulderjohn]

boulderjohn, the problem with the Marroni studies was that they ran the same ascent rate from the bottom to the surface. A 10 fpm ascent from 70 feet is definitely not the best profile -- as Ross says, you have to get OFF the bottom. Marroni did not look at the ascent type described here, with a rapid move up to 1/2 max depth, and then a slow ascent in the shallows. And, also as Ross says, bubbles don't equal DCS, or even the subjective measures of what may be "decompression stress".

Correct. As I said earlier, I speak none of this with conviction. I have read enough and seen enough contradictory information to become convinced that I can't say anything about this with any sense of confidence. I remain leery of a series of one minute stops, but my leeriness is shaky.

One explanation that I have read for the GUE Minimum Deco is that it is just a tool to do a slow ascent.

My training in minimum deco was through UTD, and it was much more than that. It was essentially a total system for NDL diving. There is a simple formula for determining maximum bottom time, and all you have to do is do the ascent as described, do a one hour surface interval, and you are good to go on the next dive. At least in theory. That system, however, was based on the understanding that you were using nitrox 32. They emphasized that it was not designed to work on air. Of course, the ascent part of it, if correct, would still make sense on a single dive on air.

 

[Spazzy]

A safe ascent rate is critical.

Safety stops are a precaution in 'no decompression' diving.

I am unaware of any evidence that additional deep/staged stops are likely to provide any advantage to you asuming you remain within the no deco limits and ascend at a safe rate.

That said, at least two reputable diver training agencies do teach deep/staged stops (e.g. GUE's minimum deco).

 

[Hatul]

There is a consensus that the shallow safety stop is beneficial, but not so for the deep stops. The reason is with deep stop if the depth is not chosen properly you can end up net ongassing into some tissue compartments and requiring longer decompression. To choose the deep stop properly you really need to know the floor-- the point at which the dominant compartment starts to net offgas, and there is no way you can know this without a computer. I think that is why the experts at DAN do not recommend adding deep stops unless they're built into the algorithm of the computer you're using.

The Galileo Sol for example can display the Profile Dependent Deep Stops that give the bubble decreasing benefit of the deep stop without the ongassing problems.

 

[dumpsterDiver]

There is a consensus that the shallow safety stop is beneficial, but not so for the deep stops. The reason is with deep stop if the depth is not chosen properly you can end up net ongassing into some tissue compartments and requiring longer decompression. To choose the deep stop properly you really need to know the floor-- the point at which the dominant compartment starts to net offgas, and there is no way you can know this without a computer. I think that is why the experts at DAN do not recommend adding deep stops unless they're built into the algorithm of the computer you're using.

The Galileo Sol for example can display the Profile Dependent Deep Stops that give the bubble decreasing benefit of the deep stop without the ongassing problems.

I really disagree with this argument. The OP is asking about a dive from 80 feet or something.. The deep stop for most recreational divers is going to be at a depth of around 40-50 feet. So even if the SLOW tissue is on-gassing at this depth, it must be at an exceedingly slow rate.. The navy tables gave us 100 minutes no deco at 50 feet.. If I hang there (at 50 for 2 minutes) are my slow tissues REALLY gonna absorb a meaningful amount of nitrogen?

My gut instinct tells me NO.

However, as I understand the mechanics, the FAST tissue will be off-gassing (kinda slowly) at this deep stop. It is my fast tissue I am most worried about nerves, brain etc. so allowing this fast tissue to off-gas a little slower for a few minutes is a theoretical benefit that I am willing to seek.

As a practical matter, most divers are using nitrox so the no-deco limit at 50 feet is even longer and the potential on-gassing is even less.

More importantly, most everyone has a dive computer now and they do calculate the effects of this deep stop. Any continued on-gassing of slow tissue during the stop at 50 is going to be picked up by the computer..

I know that my cheap one-button nitrox computer does it... when I do deco dives and I do a deep stop, it penalizes me.. My deco penalty increases on ascent (slightly) because I add a deep stop.

I don't think recreational divers need a fancy asss comp. to do a typical deep stop safely.

 

[beaverdivers]

Dive computers are like cars. Which car do you want to drive?