Deep Stops Recreational Divers

[KenGordon]

Ken, I'm curious as to which computer you have that doesn't allow you to turn off the deep stop function?

Suunto HelO2. It is an OC Trimix computer, same size as a Zoop.

 

[scubadada]

Help
What is "around 15ft"?

On a 100ft square profile for 30mins on 32% I would:
ascend at 30ft/min for 2 mins,
start slowing down around 40ft,
then do 1 min at 30, 2@ 20ft, 2@ 10ft

Total time to surface = 8-9mins.

I answered "no, I do not conduct deep stops" did I answer wrong?

That dive would be right at my NDL for a clean 1st dive with DSAT. Out of interest, why would you choose your ascent profile over my 5 min at 15 feet?

 

[dmaziuk]

I think Deco for Divers quotes a study that found most recreational divers ascend from their safety stop to the surface at 200 fpm. Perhaps we should be amazed that we don't see more obvious signs of decompression stress when this is the case?

Also 2nd degree burns from the water boiling from friction heat.

 

[boulderjohn]

Suunto HelO2. It is an OC Trimix computer, same size as a Zoop.

...running a version of RGBM, which is inherently deep stop in its design.

 

[chillyinCanada]

My computers ask if I want to turn on a DS and I don't.

 

[rjack321]

"around 15ft" has nothing to do with a deep stop, half the max depth or half the max pressure.

On a 70ft dive my "first stop" at 30ft isn't far off 1/2 the max depth (35ft) and its actually deeper than 1/2 the max pressure (70ft = 3.1ata / 2 = 1.56 ata = about 19ft)

 

[NAM001]

Deepstops in recreational dives....it sounds like a fashion statement, while most recreational divers have only a little bit of decompression knowledge. Technical divers learned about decompression theory during their courses and are aware of decompression questions that nobody has answered yet.

If you put tissue pressure and ambient pressure in a diagram, this is what a NDL dive looks like:
View attachment 516945
While descending, ambient pressure increases much faster than the gas pressure in your tissues. While you stay at depth (same ambient pressure), the tissues are ongassing. Once you reach the last point in time, where you swim up to the surface without stopping, and your tissue pressure is below the M-value (green line), your computer displays a NDL time of zero.

And the computer does this for 16 different compartments, each with their own halftimes for off-gassing. The NDL displayed on the screen is the shortest time for each of these calculations.

To off-gas, you need to get above the blue line (Pamb = Ptiss). On a dive shallower than 40m/130ft within the NDL, adding a deepstop will on-gas the mid and slower tissues even more. Doing a safety stop at 5m/15ft for three minutes is way more effective than a deepstop.
View attachment 516953

I agree with your Point on the middle TC's and continued on gassing. I think there is one flaw with that. Although your point is mechanically correct. I have to question whether or not there is any negative impact from doing it. IMO NOT from a single dive or perhaps 2 dives a day. I think to continue to use the one rule fits all is not a good idea. One rule fits all is the same as saying because I told you so. One could also say that an extra suitcase in the car will drop your millage or driving 10mph faster will do the same. when you have 10 gallons and 30 miles to drive there is no threat of being out of gas on the side of the road. For rec divers no deep stops is akin to mandatory optional safety stops.

Again from the recreatonal point of view..... One poster said they would rather do a really slow ascent and enjoy the end of the dive. I am pretty confident that if you slowed ascent rates to 20 ft/min ndls would increase and safety stops would go away also. This is all a ballancing act premissed on a 30 ft / min ascent protocol. I could make the argument that a rapid ascent fro 100 to 50 would be benificial in that remaining air lasts longer. that the 2 mins at 60 ft is less than the over all gain from tank life at a shallower depth. Its really an argument that depends on which ascent protocol elements one is willing to bend for the sake of another for the probably same outcome.

 

[NAM001]

On a 70ft dive my "first stop" at 30ft isn't far off 1/2 the max depth (35ft) and its actually deeper than 1/2 the max pressure (70ft = 3.1ata / 2 = 1.56 ata = about 19ft)

Great comment. If the rec world had control of ratio deco there would be no flexibiity to shape your ascent

 

[rjack321]

That dive would be right at my NDL for a clean 1st dive with DSAT. Out of interest, why would you choose your ascent profile over my 5 min at 15 feet?

Because in my case I reduce pressures more gradually and 15ft sucks when its surgy or wavey or most times on CCR. Vis at 20-30ft is usually way better than 15ft, so you can see and communicate better too.

You take 2.6 mins to reduce from 4 to 1.5 ata
I take about 4 mins to reduced from 4 to 1.5 ata (by the time I get to 15ft)
I don't think there's any reason 1.5-2 mins deeper than 15ft is remotely relevant from an offgassing perspective.

30ft is still well within the offgassing zone for faster tissues and on 32% the slow tissue ongassing at anything less than ~45ft is so negligible you have for all practical purposes infinite NDL time. I don't know anyone rushing up to 15ft to hang around here, even on a boat dive coming up an anchor line. Definitely not on shore dives where there's stuff to see at 20ft since its often below the wave action zone.

 

[NAM001]

I think Deco for Divers quotes a study that found most recreational divers ascend from their safety stop to the surface at 200 fpm. Perhaps we should be amazed that we don't see more obvious signs of decompression stress when this is the case?

Under the right conditions that ascent rate would be harmful. Could those conditions be met on a rec dive??????