Any downside to extending the safety stop?

[TSandM]

Think about it this way: During your dive, all your tissue "compartments" are absorbing nitrogen. When you arrive at your 15 foot stop, assuming you HAVE been deeper during the dive, no compartment is in equilibrium with the partial pressure of nitrogen at 15 feet. It takes 6 half-lives to reach equilibrium, and it's unlikely that there is any part of the body with a half-life of less than a minute. So yes, you are offgassing during the safety stop, and yes, that offgassing will continue, even if you extend the stop. So you are probably reducing the already very low likelihood of DCS by extending your stop.

And why not? Assuming the water conditions are such that current or swell/chop aren't making the stop uncomfortable, and that you are somewhere where there is something to see . . . well, we all enjoy being in the water, right? And if there is not much to see, you can enliven your stop with skills practice!

 

[redacted]

While the differences are small, your body will off-gas faster at the surface than at a safety stop. So, unnecessisarily extended safety stops are reducing NDLs for subsequent dives. When you are talking 3 to 5 minute SS, the difference would have to be measured in seconds. But if you are spending 15 minutes or more it may start to take minutes of your subsequent dive NDLs. The graphic display on my computer allows me to estimate the % loading on my lead compartment. I usually plan to remain on a SS until that loading is about 80% or less. On multi- days of 4 or 5 dives a day, that does put me doing about 10+ minutes as slower compartments move to the lead.

 

[tomfcrist]

When I was diving NC in 2010 we had great vis for most of the dives. I'd hang until I was down to 500psi. Oh yeah never know what might swim by. I kinda envy the RB'ers they can do their entire SI at 15' and then begin the 2nd dive!

I think that if you Dive NC enough, you will notice a trend. Vacationing divers and tourists tend do stop for 3-5 minutes and get back on board...... Those of us who dive NC often tend do hang for very extended periods of time. I know i have had to convince certain captains that I wasnt doing Deco a few times, and that i would rather relax under the boat for 30 minutes than get beat to death in 6 ft seas onboard the boat. Its harder to convince them of that though when you are carrying deco gas...LMAO

 

[Lorenzoid]

I think that if you Dive NC enough, you will notice a trend. Vacationing divers and tourists tend do stop for 3-5 minutes and get back on board...... Those of us who dive NC often tend do hang for very extended periods of time. I know i have had to convince certain captains that I wasnt doing Deco a few times, and that i would rather relax under the boat for 30 minutes than get beat to death in 6 ft seas onboard the boat. Its harder to convince them of that though when you are carrying deco gas...LMAO

As a visiting diver to NC, once I was back on the boat the DM/instructor I had been diving with and who had signaled me to proceed to my safety stop without him chided me for having done only a 3-minute stop. He said something like "Around here, we like to do at least five minutes." I vaguely recall he also had us do a deep (safety) stop, but that's off topic here.

 

[tomfcrist]

I think that if you Dive NC enough, you will notice a trend. Vacationing divers and tourists tend do stop for 3-5 minutes and get back on board...... Those of us who dive NC often tend do hang for very extended periods of time. I know i have had to convince certain captains that I wasnt doing Deco a few times, and that i would rather relax under the boat for 30 minutes than get beat to death in 6 ft seas onboard the boat. Its harder to convince them of that though when you are carrying deco gas...LMAO

As a visiting diver to NC, once I was back on the boat the DM/instructor I had been diving with and who had signaled me to proceed to my safety stop without him chided me for having done only a 3-minute stop. He said something like "Around here, we like to do at least five minutes." I vaguely recall he also had us do a deep (safety) stop, but that's off topic here.

That sounds accurate

 

[Bopper]

IIRC there's a pretty impressive graph in the Deco for Divers book that indicates a 5 minute safety stop will have a significantly beneficial affect on silent bubble reduction over a normal 3 minute safety stop.

 

[rx7diver]

[is] there any disadvantage from a DCI perspective to extending the safety stop at 15 feet from 3 minutes to a longer period?

Disadvantage? Well, for those of us who still dive tables, the surface interval doesn't begin until you're on the surface. (Or until you're seated on the boat--if you're really conservative!)

Safe Diving,

rx7diver

 

[scubadada]

Is there any data to indicate that a safety stop longer than 3 minutes for a NDL dive results in a lower rate of DCS? I don't think so.

 

[TSandM]

The problem with ANY intervention in recreational diving is that the incidence of DCS is already so low that, to see a statistically significant difference, you have to have very large numbers of divers and/or dives, and those dives have to be relatively provocative to expect any incidence of DCS at all.

When the Navy or DAN folks want to study symptomatic DCS, they have to construct profiles that none of us would dive. This is the reason that Doppler bubble scores are much more widely used in studies, despite the fact that they are at best an imperfect proxy for actual decompression sickness.

 

[scubadada]

The problem with ANY intervention in recreational diving is that the incidence of DCS is already so low that, to see a statistically significant difference, you have to have very large numbers of divers and/or dives, and those dives have to be relatively provocative to expect any incidence of DCS at all.

When the Navy or DAN folks want to study symptomatic DCS, they have to construct profiles that none of us would dive. This is the reason that Doppler bubble scores are much more widely used in studies, despite the fact that they are at best an imperfect proxy for actual decompression sickness.

An imperfect proxy, or biomarker, is putting it lightly

I was initially optimistic regarding DAN PDE but have grown very skepical. As Lynne alluded to, I doubt any study with an acceptable number of subjects will ever be done for recreational diving to detect a statistically signfiicant difference in DCS due to ascent strategy.