Swimming to Surface Question

[Van Isle]

Jamerson,
the beauty of no-stop diving (recreational limit diving) is that at any time you are diving within table no-stop limits, you can ascend directly to the surface and be reasonably sure that DCS will not occur. According to PADI, the closer you are to your NDL and the closer to 100' or deeper you go, the use of a "safety stop" becomes mandated instead of recommended.

Remember, however, that "swimming to the surface" doesn't mean bolting! The tables are modeled using a certain ascent rate (in PADI's case, 60feet per min) that will release nitrogen from your system. Any faster than that and you increase risk of DCS.

Keep in mind, as well, that in recreational diving almost any kind of DCS hit is better than drowning!

Given the myriad unknowns that cannot be tabulated, dive agencies always recommend diving well within the limits to prevent DCS.

Mitch

 

[Walter]

the use of a "safety stop" becomes mandated instead of recommended.

If it is mandated, it is not a safety stop, it is a staged decompression stop and you are outside the NDL.

 

[Teamcasa]

Thanks to you and others for the helpful replies. What are these "micro bubbles" made of? Nitrogen (assuming you were breathing compressed air)?

Micro bubbles can be any gas in your system. Since we build up Nitrogen by breathing compressed air, it is one of the more prevalent gases. However, all the gases in our bodies compress at depth and all are subject to expansion during the ascent.

To protect ourselves from any dangerous over-expansion of these gases, slow ascents are called for.

Others have said this and I agree, a DCS hit is better than drowning. If you (or anyone else) is concerned about the dangers of a too fast ascent, good. Just remember that with decent dive planning and good buddy skills there should be no reason (short of a full blown emergency) to make a rapid ascent.

 

[Miller64]

thanks Web Monkey,,you explained that very well for Even ME to understand

 

[Reg Braithwaite]

Jamerson,
the beauty of no-stop diving (recreational limit diving) is that at any time you are diving within table no-stop limits, you can ascend directly to the surface and be reasonably sure that DCS will not occur. According to PADI, the closer you are to your NDL and the closer to 100' or deeper you go, the use of a "safety stop" becomes mandated instead of recommended.

And:

If it is mandated, it is not a safety stop, it is a staged decompression stop and you are outside the NDL.

I go along with those who say that All Diving is Decompression Diving. It's just that:

1. For some dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of ascending at a constant rate of 30ft./minute, and;
2. For some other dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of ascending at a constant rate of 30ft./minute and executing a single deco stop at a shallow depth.

The latter point is meaningful: If the model called for a single "deep stop" at half the working depth of the dive, many OW divers would not be able to hit it and hold it consistently. A shallow stop can be easier on some dives given the fact that it's always the same depth so you don't need to figure it out, and it's close enough to the surface to offer support such as a hang bar or a marker attached to a mooring line.

So, the "mandatory safety stop" is a deco obligation and the constant ascent rate is also a deco obligation. I don't personally believe there is such a thing as a no deco dive outside of Soccer's World Cup.

 

[Thalassamania]

... I go along with those who say that All Diving is Decompression Diving. It's just that:

1. For some dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of ascending at a constant rate of 30ft./minute, and;​

No, the PADI RDP model is, I believe, predicated on a 60 fpm ascent not a 30 fpm ascent.

2. For some other dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of ascending at a constant rate of 30ft./minute and executing a single deco stop at a shallow depth.​

No, The PADI model does not call for a deep or a shallow stop. There is nothing what-so-ever in the model that indicates a requirement or even a preference for a stop. "Safety" stops came about after a study of diver ascents indicated that they were often exceeding 60 fpm, often as fast as 120 fpm. The purpose of the shallow stop was to slow the diver down and make sure that they were under control during the critical last ten feet.

The latter point is meaningful: If the model called for a single "deep stop" at half the working depth of the dive, many OW divers would not be able to hit it and hold it consistently. A shallow stop can be easier on some dives given the fact that it's always the same depth so you don't need to figure it out, and it's close enough to the surface to offer support such as a hang bar or a marker attached to a mooring line.

So, the "mandatory safety stop" is a deco obligation and the constant ascent rate is also a deco obligation. I don't personally believe there is such a thing as a no deco dive outside of Soccer's World Cup.

But the model did not call for a single "deep stop" nor did it call for a single "shallow stop" what it called for was simply a 60 foot ascent rate, which most divers seemed to be incapable of performing.

 

[Reg Braithwaite]

No, the PADI RDP model is, I believe, predicated on a 60 fpm ascent not a 30 fpm ascent.

You know what, you're right about that. I think they're the only ones suggesting 60 ft./min. I don't think it matters as much as what you said next.

There is nothing what-so-ever in the model that indicates a requirement or even a preference for a stop. "Safety" stops came about after a study of diver ascents indicated that they were often exceeding 60 fpm, often as fast as 120 fpm. The purpose of the shallow stop was to slow the diver down and make sure that they were under control during the critical last ten feet.

So you are saying their tables do not reflect their models? In that case, there is no such thing as a mandatory stop or a safety stop or anything else, it's all hokum? That their model predicts that whether I ascend continuously at 60 ft./min. from depth, stop for a fraction of a second at 15 ft., or stop for a few minutes, my risk of DCS will be negligible provided I ascend smoothly at no more than 60 ft./min.?

I must admit I am surprised at the strategy they chose for getting divers to contrpol their ascent rate and training divers on the purpose of the safety stop. Am I the only person wandering around thinking that they teach divers to believe that the off-gassing during the safety stop is meaningful?

This doesn't change my opinion that all diving is decompression diving in the slightest, of course. I will reword what I said about the PADI protocol. It predicts that:

1. For some dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of a diver trying their best to ascend at a constant rate of 60ft./minute, and;
2. For some other dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of a diver trying their best to ascend at a constant rate of 60ft./minute, then trying their best to stop at 15', then trying their best to rise to the surface under control.

Either way we put it, the PADI protocol calls for decompression and not bolting to the surface.

 

[Thalassamania]

You know what, you're right about that. I think they're the only ones suggesting 60 ft./min. I don't think it matters as much as what you said next.

When the RDP was developed the standard ascent rate (U.S. Navy) was 60 fpm, so the RDP was designed for that same rate.

So you are saying their tables do not reflect their models? In that case, there is no such thing as a mandatory stop or a safety stop or anything else, it's all hokum? That their model predicts that whether I ascend continuously at 60 ft./min. from depth, stop for a fraction of a second at 15 ft., or stop for a few minutes, my risk of DCS will be negligible provided I ascend smoothly at no more than 60 ft./min.?

The tables reflect the models. You are correct in your assumption that if you stay within the no-D limits of the RDP and you ascend no faster than 60 fpm you'd . be in pretty good shape. Would a three minute at 10 fsw stop hurt you? No. Would it help you? Probably not ... you don't have a problem, well you probably don't have a problem ... it is a statistical thing.

I must admit I am surprised at the strategy they chose for getting divers to contrpol their ascent rate and training divers on the purpose of the safety stop. Am I the only person wandering around thinking that they teach divers to believe that the off-gassing during the safety stop is meaningful?

PADI was just following the bandwagon, it was not their strategy.

This doesn't change my opinion that all diving is decompression diving in the slightest, of course. I will reword what I said about the PADI protocol. It predicts that:

1. For some dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of a diver trying their best to ascend at a constant rate of 60ft./minute, and;
2. For some other dives, the model PADI uses predicts that the decompression required to keep the risk of DCS to a negligible level consists of a diver trying their best to ascend at a constant rate of 60ft./minute, then trying their best to stop at 15', then trying their best to rise to the surface under control.

Either way we put it, the PADI protocol calls for decompression and not bolting to the surface.

There is no scientific or medical basis for (2), that was added by the lawyers not those with a background in decompression.

But a three minute, ten foot stop will not hurt you, at least from a decompression or practice standpoint.

"Safety Stops" are antique artifacts. In this day of 30 FPM, computer controlled ascents "safety stops" are really irrelevant. I say that as one of those who was in on originating them. The idea of safety stops came out of some research that showed that recreational divers were, in point of fact, making their ascents between 100 and 120 feet per minute, back when a standard ascent was 60 fpm. The ascent problem was noted by the National Underwater Accident Data Center, it was investigated and confirmed by Glen Egstrom at UCLA, the safety stop was suggested by Andy Pilmanis of the USC Catalina Lab Chamber back in the 1970s. It was first adopted by NAUI after the AAUS Decompression Computer Workshop where Bruce Bassett (as I recall) suggested perhaps a stop between 20 and 10 feet for two to three minutes would be every bit as effective as actually getting divers to slow down to 60 fpm. In addition it would cover most errors of one depth too deep or one time too long.

Then along came dive computers with ascent meters and such and the reason for the stop was forgotten, just the procedure was remembered.

The reality is that with a 30 FPM ascent you're not going to have detectable bubbles anyway. If you are using 60 FPM based tables (and remember that the original U.S. Navy tables were almost based on 120 FPM to satisfy the needs of Doug Fane's UDT folks) Spenser did show that a 60 fpm ascent following 50 min at 2.8 ata would exhibit bubbles in some cases. But ... I believe that the PADI tables were doppler tested and a 60 fpm ascent within the limits of those tables did not show bubbles, making a stop a waste of time.

 

[Reg Braithwaite]

When the RDP was developed the standard ascent rate (U.S. Navy) was 60 fpm, so the RDP was designed for that same rate.
The tables reflect the models. You are correct in your assumption that if you stay within the no-D limits of the RDP and you ascend no faster than 60 fpm you'd . be in pretty good shape. Would a three minute at 10 fsw stop hurt you? No. Would it help you? Probably not ... you don't have a problem, well you probably don't have a problem ... it is a statistical thing.

PADI was just following the bandwagon, it was not their strategy.
There is no scientific or medical basis for (2), that was added by the lawyers not those with a background in decompression.

I was responding to someone who said that if a table shows a mandatory safety stop, it is a decompression dive. From your remarks, I conclude that PADI's mandatory safety stops are lawyer-ese and have no statistical imfluence as long as we follow the ascent protocol carefully.

From this, I conclude that you can take one of two roads:

• You can say that all PADI NDL diving is no decompression diving , even if a "mandatory" stop is indicated, because the mandatory stops are hokum, or;
• You can say that all diving is decompression diving, and that even if you ignore the stops added by lawyers you still must follow an ascent protocol and not bolt for the surface.

I have learned to take the latter line of thinking. Thanks to your clarifications, I see that the PADI tables are not well-mapped to any contemporary understanding of decompression. (That doesn't really surprise me given everything I have seen, heard, and read so far in my short diving career.)

Touching on another argument in this thread, I agree that given the choice of drowning at depth or risking DCS at the surface, risking DCS is the better choice. That being said, I am wary of false dichotomies. Specifically, I am wary of assuming that just because bolting to the surface and risking DCS is far more acceptable than drowning, that it must somehow be an acceptable strategy for managing emergencies in recreational diving.

There are tons and tons and tons of things we can do to avoid putting ourselves in the place where those are the only two options, from skills development and training to partner selection to practices in the water to gear selection to gear maintenence to gas selection to gas management to... the list of ways to avoid bolting to the surface as a last resort goes on and on.

I am humbled by the depth of knowledge you have shared with us and the clarity with which you have explained the history and reasoning behind the "safety stops." But I don't want to get distracted from a fundamental issue, which is that single tank, recreational, open water diving is still overhead diving.

 

[Tortuga68]

Touching on another argument in this thread, I agree that given the choice of drowning at depth or risking DCS at the surface, risking DCS is the better choice

Risk being the key & subjective word

I doubt anyone would choose the former over the latter in your example, but there are plenty of recorded instances of people wishing they had

The point being that many of those people had the choice to take another option - so being a 'thinking diver' is always the best option