Riding GF99 instead of mandatory/safety stops

[boulderjohn]

Well the NEDU study is fairly relevant here even, if they didn't test VPM or RGBM vs Buhlmann which would have both more directly applicable to recreational/sports divers.

Writing the article I did required extensive communication with Dr. Simon Mitchell, and in that communication he made his belief clear. Contrary to the smug statements of the "all dives are decompression dives" folks, he says there is a clear difference. The NEDU study's clear implication for decompression dive ascents does not carry over to NDL dives. In that area, there is simply not enough clear evidence upon which to form an opinion.

 

[rjack321]

Writing the article I did required extensive communication with Dr. Simon Mitchell, and in that communication he made his belief clear. Contrary to the smug statements of the "all dives are decompression dives" folks, he says there is a clear difference. The NEDU study's clear implication for decompression dive ascents does not carry over to NDL dives. In that area, there is simply not enough clear evidence upon which to form an opinion.

I was using the phase "recreational/sports diving" to include all of us diving for fun, not in an NDL vs deco sense. So non-commercial, non-military.

 

[Nick_Radov]

Also going from memory, he referenced Bruce Weinke for support, but someone posted a video of Bruce Weinke specifically stating that the switch from 21/35 to EANx 50 was not dangerous. The fact that Weinke felt compelled to make that video suggests that he must have been getting cited for that fairly often.

You might be referring to this Suunto video with Dr. Bruce Wienke.

Now, when you get in the shallow zone, like when you get into the 50 foot zone, I mean the 70 foot zone or even shallower, switching over to 50/50 heliox or 50/50 even nitrox. In that zone ICD doesn't seem to be as much a problem or as causative of isobaric counter diffusion super saturation as it does in deeper depths. So the problems with ICD are magnified as you go deeper and deeper. As you get shallower and shallower if you have been following the decompression glide path that is safe within your model calculations and efficient. When you get into the 70 foot zone or so, switching to 50/50 heliox or 50/50 nitrox even though the 50% nitrogen may be higher than what you're coming up on your switch gas seems to be OK because of the gas dynamics.

His general concern seemed to be with doing extreme tech dives in the 500+ ft range on a high helium mix, then switching to air on ascent for deep deco stops. Which may be valid but it's outside my personal experience, and we have so little real world data from other divers that it's probably difficult to draw any reliable conclusions. Doing bounce dives in that depth range with accelerated deco seems to be a game of "Russian roulette" anyway with numerous anecdotal reports of severe DCS that seem random and unrelated to ICD.

 

[old frogman]

Well ICBD doesn't exist outside of diving bells and commercial scenarios where the divers are immersed in a helium gas. No sports diver ever does this because you'll freeze into a popsicle with trimix in your drysuit - especially with the really high mixes like 10/70 or 8/80

But you seem to think otherwise based on chatgpt or google or some 2005 era bro-science, it's hard to tell.

I think that what you are trying to say is that ICD may not occur today because divers are using more appropriate gas switching gases at depth and/or doing switches to high N2 gas mixtures in the shallows.

However, in the past some divers ascending from 100m dives were switching from trimix to air at 50m or 60m in an attempt to reduce their decompression obligation. Some had issues like vertigo and vomiting.

In conclusion, the risk associated with ICD has been controlled/reduced however the risk is still there. As long as you conduct gas switching the risk remains. In risk management parlance risk cannot be eliminated but reduced to a level that is as low as reasonably practicable.

Also, please refrain from trying to shut down contributors by making defamatory statements such as the last sentence in your post. Logical, well researched and well delivered explanation are better accepted by the diving community.

 

[Blackcrusader]

Writing the article I did required extensive communication with Dr. Simon Mitchell, and in that communication he made his belief clear. Contrary to the smug statements of the "all dives are decompression dives" folks, he says there is a clear difference. The NEDU study's clear implication for decompression dive ascents does not carry over to NDL dives. In that area, there is simply not enough clear evidence upon which to form an opinion.

I love reading all the replies in these threads. I use a Shearwater which of course has SurfGF. In some ways this discussion goes beyond my diving skills regards those doing deep deco dives. Sure I might do a light back gas deco dive at depths generally less than 45m depth.

Would I use the surf GF to understand could I safely go to the surface without a safety stop on an NDL dive. Sure nice to look at but I always do a safety stop and actually find on some dives many things to see and take photos and videos of at 5m depth anyway and sometimes hang there for 10 - 15 minutes.

For me as a recreational deco diver I am more interested about on gassing off gassing and just have safe dives. In 39 years of diving I have never had a DCS hit. Also without this forum I would not see these discussions. Most rec divers don't know about this forum and just want to have fun without understanding the deep learning applied to this type of thread. Most people have never read Deco for Divers either.

 

[rjack321]

You might be referring to this Suunto video with Dr. Bruce Wienke.



His general concern seemed to be with doing extreme tech dives in the 500+ ft range on a high helium mix, then switching to air on ascent for deep deco stops. Which may be valid but it's outside my personal experience, and we have so little real world data from other divers that it's probably difficult to draw any reliable conclusions. Doing bounce dives in that depth range with accelerated deco seems to be a game of "Russian roulette" anyway with numerous anecdotal reports of severe DCS that seem random and unrelated to ICD.

This was basically what I meant by "Exley" dives. He was doing some deep air or super deep END switches 4 to 8+ ATA deeper than anyone would do today. The data for those are, needless to say, somewhere between sparse and non-existent.