Two safety stops?

[danvolker]

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.....

 

[bbarnett51]

I was certified NAUI in 1992 on Grand Cayman. We did this on every deep dive. Then I came back and started geting certs through other agencies and did not continue the practice. I cant tell any difference personally. Usually after back to back deep dives(100ft plus) Ill spend a little extra time at 15' but that is based on no sciemce whatsoever!

 

[billt4sf]

From what I remember reading on SB, the idea of safety stops in the first place had little to do with off-gassing and were implemented so folks would slow down because a lot of divers were ascending to fast. As a side benefit it did allow some additional time to off-gas.

The article makes clear that safety stops are important if only to get divers to think about how fast they are ascending and to ascend more slowly. The article also states that there were several studies done where people were tested after various profiles and those who did a deep stop as well as a safety stop had fewer "silent bubbles" than those that simply ascended slowly.

Apparently the new recommendation is 30 feet per minute; I was taught 60 feet per minute about 7 years ago.

And again -- they quoted DANs data as suggesting that those at highest risk for DCS are those that makes multiday, repetitive dives. They said that DAN recommends taking a day off, or slowing the number of dives / day towards the end of the vacation. I am thinking that the slower ascent rate and the multiple stop routine might be appropriate for us, since I highly doubt that we will take a day off after spending thousands of dollars to get there to dive (just being honest about my limitations).

- Bill

 

[MXGratefulDiver]

Considering this sounds like its all about the money that can be harvested , then my suggestion is just a different moneymaker....another course ..... An. O2 stop course for recreational divers....-

Teaching someone to make an extra precautionary stop is simply a change from how ascents were previously taught ... nobody raised the price of the class because they started teaching it.

What money are you referring to?

... Bob (Grateful Diver)

 

[rmh84]

First I've heard of it - but I think it's a great idea, especially when you're pushing rec limits anyway.

I can see certain conditions where you might prefer to not, but if you can why not do it? Give you a chance to work on your bubble ring skills too (yes, this is what I do on my safety stops now that I've got bouyancy all worked out!).

 

[MXGratefulDiver]

From what I remember reading on SB, the idea of safety stops in the first place had little to do with off-gassing and were implemented so folks would slow down because a lot of divers were ascending to fast. As a side benefit it did allow some additional time to off-gas.

... ascent rate has everything to do with off-gassing. As you ascend you're reducing the ambient pressure on your body as well as the pressure of the gas you're breathing. Both of those factors directly affect how quickly your body will offgas. The former affects your body's ability to hold dissolved gas in solution ... less depth = less pressure = less dissolved gas in soluton = more bubbles. The latter determines the pressure differential between the gas coming out of solution in your body and that entering your lungs ... the greater the pressure differential, the faster the gas wants to migrate from the blood to the lungs. The idea of a safety stop is to allow that pressure differential to "catch up" a bit ... enabling your lungs to be a more effective gas trap for what's coming out of solution.

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)

 

[racerx_]

I seem to remember a discussion on this before on SB.. There were varied opinions, same as here, but I thought the general consensus was to make the deep stop effective, the idea would be you hit your max depth, poke around, and then reasonably quickly move to your deep stop (rather than slowly sightseeing for 20minutes up to that depth). So that you are getting the off gassing benefits of it rather than just spending more time on gassing at depth.

FWIW I turned the deep stop function of my computer on some time ago but I think it only kicks in on deeper dives so it hadnt prompted me. My last trip I hit about 25meters and it had me doing a deep stop at half depth. It was a shore dive so we basically did a really extended safety stop as we swam all the way in to shore slowly. Definitely felt a bit better post dive on that dive and the subsequent when I paid more attention to stops, and ascent profiles. The previous two days of diving I was tired out and fell asleep by 8 or 9pm, and ended up with a headache after each dive.. That's not scientific research but personally it seemed to help me.

 

[danvolker]

Teaching someone to make an extra precautionary stop is simply a change from how ascents were previously taught ... nobody raised the price of the class because they started teaching it.What money are you referring to?... Bob (Grateful Diver)

Less DCS for the 25 percent that probably should not dive.....meaning more profit with less accidents....the agency quest to increase the number of divers. For the healthy divers that don't need this, it means shorter bottom times or using larger tanks...it impacts the diving experience in a negative way...I am well aware this is an argument I am not going to win

 

[DivemasterDennis]

My observation is that same as Bob's. People do a safety stop and then ascend 3 times as fast as thy should for that last 15 or 20 feet. As far as a second safety stop goes, Debbie and I do them if depth from which we are ascending directly to the surface exceeds 70 feet. A lot of our deep dives are actually multi-level dives, and the dive profile itself gives a safety margin. At some locations ( many shore dives in Bonaire and Maui ), the safety stop is actually done as part of the dive. Hanging out at 15 to 20 feet on the top of the wall after having started the bottom portion of the dive at 60 to 120 feet provides a great safety stop. The "intermediate stop can alos be a pause at the 1/2 depth level on a wall as you continue your dive atthat depth and then ascend after an interval at that depth. Safety stops are just that- for safety margin increase, and I am all for increasing safety margins. However, as Bob points out above, ascent rate remains a critical factor in DCS risk. Ascend just as slowly after each safety stop.
DivemasterDennis

 

[MXGratefulDiver]

Less DCS for the 25 percent that probably should not dive.....meaning more profit with less accidents....the agency quest to increase the number of divers. For the healthy divers that don't need this, it means shorter bottom times or using larger tanks...it impacts the diving experience in a negative way...I am well aware this is an argument I am not going to win

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)