Two safety stops?

[dumpsterDiver]

Nor should you win it ... you're arguing against something that has no downside except to "weed out" people who you think shouldn't dive.

One minute pause at half your deepest depth, Dan ... it doesn't reduce your NDL, it doesn't require much gas, it doesn't shorten your dive in any way.

That's a damn silly argument on a Basic Discussion forum. Might carry a bit more weight if we were talking tech diving.

... Bob (Grateful Diver)

It makes a lot of sense... I learned a long time ago how best to deal with novice divers and openwater ascent. As a Divemaster on a charter boat. I totally MADE UP a rule.. we are ALL gonna stop at 30 feet and then we will all check each other's air and THEN we will slowly ascend to our safety stop. I devised this "rule" because I got so damn tired of people blowing by their 15-20 ft safety stop. They would TRY to stop there (15-20), but way too many would just lose it and blow up to the top. Once I figured out to make up a rule that we would all stop at 30, some people would screw up and miss the stop, but pretty much everybody would stop their ascent by 15 feet and then they could swim down and "show me their air". It was a silly little rule, but it was incredibly effective in preventing uncontrolled ascents to the surface.... Telling recreational divers (tourists) who rarely dive deep than 80 or 90 to stop at 40 feet or so (for 60-90 seconds)... will have SIGNIFICANT advantages in this regard.

 

[billt4sf]

The most common place I see people ascending too fast is after their safety stop is completed. I've seen this more times than I care to think about ... people religiously do their three minutes, look at each other, give each other the thumb's up ... and 5 seconds later they're on the surface ... which amounts to an ascent rate of about 180 feet per minute ... ... at the very point in the dive where a slow ascent rate is most critical.

It should take at least 30 seconds to surface after a safety stop ...

... Bob (Grateful Diver)

Thanks for this!!

 

[Ayisha]

For those not so sure about whether a deep stop is a good idea, think of it as you would a multilevel dive.

Is there any reason not to do a multilevel dive, say for example, x amount of time at 100 feet, slowly work your way up to around 50 feet for x minutes, then around 20 feet for 5 minutes? We often do this on wall dives and some wreck dives, spending more time around half-depth than 1 - 3 minutes. I would much rather do a deep stop and/or a multilevel dive than a square profile, for example, 130 feet straight up to the safety stop and then the surface.

I always plan to do a 1 to 2 minute deep stop around 50 feet with like-minded buddies. With some buddies on particularly deep dives, we'll stop between 30-60 seconds every 10 feet until our safety stop for at least 5 minutes at 20 feet, then another minute at 10 feet, and then slowly to the surface, controlled all the way. I'd rather be safe than sorry.

 

[TSandM]

There are some reasonably good data that, if you are doing a square profile, a half-maximal-depth stop reduces bubble grade on surfacing. It should not be unduly prolonged -- one to two minutes is enough -- and the ascent TO that stop has to be properly expeditious, as should the subsequent ascent to safety stop depth. Of course, not everyone who bubbles is symptomatic, but it would SEEM attractive that if you can reduce bubbling, you should reduce the RISK of symptoms.

This is not to be confused with "deep stops" for staged decompression diving, which are much more controversial, and for which there are much poorer data.

No one has studied terrain-based diving, with the gradual, slow descent and ascent that are the nature of that type of dive.

 

[Steve_C]

DD's post about the micro hits from the speargun without a deep stop, parallels something George Irvine, Bill Mee and I learned in the mid 90's.... We were in a Doppler study , and to make a long story short....it indicated we could do ridiculously aggressive profiles and still clear very fast with very little bubbling....but when carrying my big double barrel Ultimate gun, there would be significant bubbling from a 120 foot dive for 20 minutes in the arm carrying the heavy gun..... For the study, this was a no stop dive...they were trying to see what would cause bubbling...how much....The solution I employed from then on, was that at my stop (or stops), I would clip off the gun...or heavy camera....so that the constricted blood vessels in the arm carrying the load could regain good blood flow by letting the muscles relax....this worked perfectly.....

Interesting. I had not heard that before. Suppose the same would hold when ascending an anchor line in current. Try to keep your arms relaxed to the extent possible.

 

[antattack]

@TSandM

I did not know that my typical dive profile has not been studied! Living in Santa Cruz, CA, I mostly do shore dives into the Monterey Bay. When we dive sites like North Monastery beach, we drop down to 30' and kick out to the canyon wall at 60' ten minutes later and from there we can get to the sport limit in another minute or two. We explore our planned depth, then we work our way back up the terrain for the next twenty minutes followed by a three minute safety stop and crawl through the waves onto the beach.

I've never intentionally or un-intentionally incurred a deco obligation doing this dive profile as measured by tables or computer. I always assumed this was a very safe dive profile. It would be nice to move beyond assumption and get some real data.

If anyone wants to do a study of divers doing terrain dives, this would be an ideal site. If you need a subject to study, I'd be happy to inform my wife that I have to go diving every weekend for three months straight for the benefit of SCIENCE!

 

[danvolker]

Interesting. I had not heard that before. Suppose the same would hold when ascending an anchor line in current. Try to keep your arms relaxed to the extent possible.

Absolutely...the last thing you would want if you were heavily saturated with nitrogen, is to have to work your arm and core muscles hard on pulling up the anchor line.

We always had had very relaxing ascents from our tech dives, free drifting, and anything of weight clipped off.
I think there is a wide range of off-gassing potential for the general diving gene pool. But whatever speed each of us off-gasses at, each of us needs to avoid any real muscle work on our ascent and in deco stops....
My wife Sandra used to get sore elbows from diving in Boynton beach on hour long 60 foot dives----she had a heavy pro-level camera. Once I got her to clip off, the sore elbows never happened any more.
While a deep stop "may" have helped a little, this worked flawlessly....and the deep stop really would not help to regain bloodflow in contracted muscles with constricted blood vessels.

 

[MXGratefulDiver]

@TSandM

I did not know that my typical dive profile has not been studied! Living in Santa Cruz, CA, I mostly do shore dives into the Monterey Bay. When we dive sites like North Monastery beach, we drop down to 30' and kick out to the canyon wall at 60' ten minutes later and from there we can get to the sport limit in another minute or two. We explore our planned depth, then we work our way back up the terrain for the next twenty minutes followed by a three minute safety stop and crawl through the waves onto the beach.

I've never intentionally or un-intentionally incurred a deco obligation doing this dive profile as measured by tables or computer. I always assumed this was a very safe dive profile. It would be nice to move beyond assumption and get some real data.

If anyone wants to do a study of divers doing terrain dives, this would be an ideal site. If you need a subject to study, I'd be happy to inform my wife that I have to go diving every weekend for three months straight for the benefit of SCIENCE!

Profiles on shore dives are usually specific to the terrain ... and multilevel stops specific to what you are going down there to look at. Here's a typical "deep" recreational profile at one of our more popular Puget Sound dive sites. This is the one I use as an example in my gas management seminar, in fact. The red dashed line is the dive plan, superimposed over the actual dive. The "stops" are points of interest that we've planned to explore on the way up. As you can see, there are "stops" at 60 and 40 feet, as well as the safety stop.

This is a dive which is typically done using a larger single cylinder and EAN32 ... and due to its popularity, one I chose specifically to point out why you shouldn't even attempt it on anything smaller than a 100.

... Bob (Grateful Diver)

 

[herbdb]

When I did my first deep ocean dives, I was taught that there is little benefit to a very slow ascent during the deepest portion of the ascent from a deep dive. This allowed for higher ascent rates (up to 60'/min below 60' depth). Then to make a 2 min stop at 60' followed by a slower (max 30'/min) ascent to a 15 ft safety stop.

Could some of you more experience divers comment on what I was taught and still practice?

 

[TSandM]

HERE is the very good article that began my understanding of this stuff. (Warning -- that's a Deco Stop thread and you will have to register there to read it.)

What decompression software does, looking at a variety of compartments and loading and unloading, is generate an ascent profile that is generally faster in the deep portion, and slows gradually as you approach the surface. The shallower you are, the longer the stops you are doing, and although the precise shape and distribution of stops is dependent on the program and how you set it, they all look like that.

It is not NECESSARY to shape recreational ascents this way, at least in theory. The whole idea behind NDLs is that you are free to proceed directly to the surface at the prescribed ascent rate, assuming you can keep your ascent rate quite constant. Safety stops, as I understand it, were inserted to help control ascents in the shallows, because divers weren't doing it, but they also have the effect of putting a more horizontal "tail" on the ascent profile.

Since DCS is vanishingly rare in recreational divers who stay within all prescribed limits (NDL time and ascent rate), it is difficult to prove that any change in ascent strategy is tremendously meaningful. Studies generally use Doppler bubble scores as a surrogate for DCS symptoms, but there is a problem with that, because some people have high bubble grades and no symptoms. Marroni's studies did show that a very slow ascent rate from the bottom is one of the worst approaches for bubbling, but he has also looked at a multi-stop profile and found it reduced bubbling ([abstract] USE OF A DEEP (15M) AND SHALLOW (6M) STOP FOLLOWING 25 METER NO-DECOMPRESSION DIVES REDUCES DECOMPRESSION STRESS (AS OBSERVED BY DOPPLER-DETECTABLE BUBBLES) WHEN COMPARED TO EITHER A DIRECT ASCENT, OR DIRECT ASCENT WITH ONLY A SHALLOW STOP).