More conservative/"alternative" diving profiles?

[Ouvea]

I'm a bit confused as to how deep stops have bearing on an NDL recreational dive profile. I thought deep stops were part of a decompression schedule for technical diving where you have required decompression stops. The OP inquired about ascent profiles while still within NDL. If you have a required stop, then aren't you beyond the confines of a recreational dive profile?

Some agencies such as GUE recommends ascending to 50% of maximum depth at a rate of 30ft/minute then ascending to the surface at a rate of 10ft/minute, instead of performing a 3 minute stop at 15 feet. If you look a the overall ascent time, both strategies yield fairly similar results in terms of total ascent time, however the ascent curve profile is quite different.

 

[Jay]

some good reading in this thread: Evolving Thoughts on Deep Decompression Stops

 

[lowwall]

I'm a bit confused as to how deep stops have bearing on an NDL recreational dive profile. I thought deep stops were part of a decompression schedule for technical diving where you have required decompression stops. The OP inquired about ascent profiles while still within NDL. If you have a required stop, then aren't you beyond the confines of a recreational dive profile?

The problem is that people apply the same term to two completely different things. One of the things called deep stops refers to an additional optional (aka "safety") stop from 1 to 3 minutes at around half your max depth on a non-deco dive. The other refers to deco algorithms that start deco stops much deeper than traditional tables/algorithms, usually deeper than half depth.

 

[A_Buhlmann]

I'm a bit confused as to how deep stops have bearing on an NDL recreational dive profile. I thought deep stops were part of a decompression schedule for technical diving where you have required decompression stops. The OP inquired about ascent profiles while still within NDL. If you have a required stop, then aren't you beyond the confines of a recreational dive profile?

Some agencies such as GUE recommends ascending to 50% of maximum depth at a rate of 30ft/minute then ascending to the surface at a rate of 10ft/minute, instead of performing a 3 minute stop at 15 feet. If you look a the overall ascent time, both strategies yield fairly similar results in terms of total ascent time, however the ascent curve profile is quite different.

Yes, you are correct, I inquired about the "Pyle stop", while I'm well within NDL for that depth(even more "ongassing" would still be OK because of the NDL being respected. I read it somewhere that Dr. Pyle started to do it because he realised that it significantly diminished fatigue.
As to the ascent rate, I would still prefer the safety stop plus the slower ascent rate from 15ft to surface...

 

[A_Buhlmann]

Linked to reducing endothelial dysfunction post-dive when ingested pre-dive. I guess it is one of those rare 'conveniently good news' things - although I trust it to be sufficiently minor.
Here is a study based on 30g of 86% chocolate taken 90min pre-dive: The effect of pre-dive ingestion of dark chocolate on endothelial function after a scuba dive. - PubMed - NCBI

Other things you may want to do:
- aerobic exercise
- sauna
- getting on those body vibration machines
- resting and hydrating properly
- making sure you do not have dietary deficiencies
- stay warm during and between dives to allow for efficient off-gassing
- ...

Nice! in the book "Scuba Physiological" I read about the effects of a pre-dive run in the last 24h for preventing DCS. Besides hydration the others are fairly new to me. Thanks

 

[Fastmarc]

My Mares Puck which runs the RGBM (reduced gradient bubble model) algorithm inserts a deep stop if the NDL went below 5 minutes. The length of the deep stop was user selectable at either 1 or 2 minutes.

Interestingly I've dived with a Nemo Wide for several years and have gone below 5mins NDL, but never saw it recommend a deep stop. Not sure if that was because of my usually slow ascent finishing the dive.

 

[dmaziuk]

I'm a bit confused as to how deep stops have bearing on an NDL recreational dive profile. I thought deep stops were part of a decompression schedule for technical diving where you have required decompression stops. The OP inquired about ascent profiles while still within NDL. If you have a required stop, then aren't you beyond the confines of a recreational dive profile?

Correct. Some computers have an optional mid-way stop, these days called "profile-dependent intermediate stop" to avid the scary bad d-word, while older ones still use it. But it's typically a 1-2 minute stop, that's too short to matter for any tissue compartments except the fastest one(s). On top of which at recreational depth it's at 20 metres or shallower, where pressure difference is not that great. As a result its bearing on a recreational no-stop dive profile is to slow down the ascent. On-gassing in slow tissues should be somewhere between negligible and non-existent.

 

[EFX]

If we are going to talk about deep stops we shouldn't forget that one of the reasons is to reduce bubble size and bubble quantity. The RGBM algorithm on my Mares Puck uses both a dissolved gas model and a bubble model to prevent DCS. While the dissolved gas models limit the quantity of bubbles they do not track bubble size.

Bubble models reduce bubbles beyond a critical size and quantity. The idea is that it's not just bubble quantity but bubble quantity beyond a certain size that causes DCS. Bubbles expand when their internal pressure exceeds the sum of the external pressure and their surface tension. The problem for divers, according to bubble model theory, is that as bubbles expand to a certain point the surface tension becomes less which greatly increases the ability of the bubbles to expand even more which further reduces the surface tension. The expanding bubbles cause the internal pressure to decrease allowing the dissolved and free gas to enter the bubble which raises their internal pressure adding to their growth. The deep stops halt bubble growth by ambient pressure decrease while allowing time for some of the inert gas to off gas which then limits the reservoir of inert gas available for bubble growth. The hoped-for result is that bubbles do not grow beyond a critical size of a certain quantity.

 

[Nemrod]

Nearly all computers and tables today are very conservative. We used to use the original Navy tables, 60 fpm ascent, no safety stop. Diving the rigs (some but not including me) would go to stupendous depths, spear a fish, drag it up and go right back down. I was never quite that stupid. I have a relative by marriage who is paralyzed waist down from exactly that.

Deep stops, hmmm. If I have gone below my current (wife specified) set soft limit of 100 feet and push the deco limit to the edge (of the tables or computer) then I will do a short deep stop, more like a hesitation. Then mosey on up to 30 feet and from there a slow rise to 15/20 feet for at least three minutes (or until my computers back out of the yellow). Then drift on to the surface. If I have been doing shallower dives then I ascend to 15/20 feet and remain there for three minutes or until my computers back out of the yellow and then drift to the surface. Once I crossed the big 60 yo I have become increasingly conservative. I have a lot of things still on the plate and would prefer not to be bent. Never have been despite many very deep dives, deco and tech/cave type stuff. The cave stuff, you will never see me in a cave ever again and on purpose deco dives only for something special.

I suspect any fatigue you are having is more a result of physical exertion, your body dealing with the thermal affects of even warm water more than the nitrogen off gassing.

N

 

[jgttrey]

Correct. Some computers have an optional mid-way stop, these days called "profile-dependent intermediate stop" to avid the scary bad d-word, while older ones still use it. But it's typically a 1-2 minute stop, that's too short to matter for any tissue compartments except the fastest one(s). On top of which at recreational depth it's at 20 metres or shallower, where pressure difference is not that great. As a result its bearing on a recreational no-stop dive profile is to slow down the ascent. On-gassing in slow tissues should be somewhere between negligible and non-existent.

This. In a recreational context, it's almost certainly harmless (but likely of little benefit if you are otherwise making a conservative ascent).

If you want to add some conservatism, that extra minute or two or three is best spent in two places: (1) at your normal safety stop and (2) in a slow ascent from there to the surface. I'd far rather spend that extra minute on that last 15' ascent. Amazing how many people spin themselves into a tizzy about whether to stop for a minute deep, and then bolt from their safety stop to the surface in 20 seconds.