My Journey into UTD Ratio Deco

[Storker]

If ice cold towards the end of a dive, on the face of it, that would favor shallow stopping disproportionately.

Why? How? If on- and off-gassing are affected the same way, how would that favor shallow stopping instead of just increasing the time required?

 

[CAPTAIN SINBAD]

So in a nutshell...
Way back when people (1980s) were diving experimental tables by Hamilton and others
They added deep stops and that helped mitigate them to some extent (1990s)
Yount/Wienke published their bubble work (1998- 2000ish)
People added way too much time deep and/or shortened the overall time because they suspected they were avoiding the "bend and mend" which was previously suspected.
VPM hits the market about this time as a commercial product - looks so scientific too...
Many people add too much time deep with GFs of 20/85 and such stuff, RD is 5/95ish reflected the misnomer that deep stops avoid bubbles forming so you don't have to get rid of them later.
VPM 2+ seems to confirm that deeper is better even if shorter overall.

Finally we start getting hard data that this is all just a thought experiment and some divers are still stuck in 2005 era deep stops...

True but the modern scientific recommendation ultimately comes out to be the same prolonged shallow stops that got a lot of guys like JJ and GI3 bent. This is why some of these old school DIR people like AG would say that even before Navy studies were done, we already did that pure Buhlmann shallow stop which is being propagated now and we have gotten skin bends so no thanks. Keep your science to yourself we want to be safe. Been there, done that and gotten bent! GI3 is talking exactly when he talks about skin bends and those other symptoms.

There seems to be a disconnect between NEDU and the collective dives done in early GUE days here and I am wondering if Helium could be a factor? NEDU people were doing deep air and these guys were experiencing symptoms on Helium so while there is some research to show that Helium off gases at the same rate at nitrogen, the same paper also states that "a few data exists that directly compare the decompression obligation resulting for Helium Oxygen and Nitrogen Oxygen of bounce dives for identical depth and duration."

https://www.physiology.org/doi/pdf/10.1152/japplphysiol.00944.2014

The other explanation could be that some people just respond better to deep stops and they are a minority. When DIR began, some mathematical co-incidence resulted with them ending up together and that is why their collective trial and experimentation resulted in deep stops.

 

[kensuf]

True but the modern scientific recommendation ultimately comes out to be the same prolonged shallow stops that got a lot of guys like JJ and GI3 bent. This is why some of these old school DIR people like AG would say that even before Navy studies were done, we already did that pure Buhlmann shallow stop which is being propagated now and we have gotten skin bends so no thanks. Keep your science to yourself we want to be safe. Been there, done that and gotten bent! GI3 is talking exactly when he talks about skin bends and those other symptoms.

There seems to be a disconnect between NEDU and the collective dives done in early GUE days here and I am wondering if Helium could be a factor? NEDU people were doing deep air and these guys were experiencing symptoms on Helium so while there is some research to show that Helium off gases at the same rate at nitrogen, the same paper also states that "a few data exists that directly compare the decompression obligation resulting for Helium Oxygen and Nitrogen Oxygen of bounce dives for identical depth and duration."

https://www.physiology.org/doi/pdf/10.1152/japplphysiol.00944.2014

The other explanation could be that some people just respond better to deep stops and they are a minority. When DIR began, some mathematical co-incidence resulted with them ending up together and that is why their collective trial and experimentation resulted in deep stops.

So, I was one of the WKPP guys doing mixed gas diving at Wakulla (and throughout Leon Sinks) in the 90s. I can assure you, guys got bent regularly.

 

[CAPTAIN SINBAD]

So, I was one of the WKPP guys doing mixed gas diving at Wakulla (and throughout Leon Sinks) in the 90s. I can assure you, guys got bent regularly.

You mean they got bent doing pure buhlmann old school or the bends increased after adding stops? Thanks.

 

[kensuf]

Both.

 

[CAPTAIN SINBAD]

Yes I suspected.

 

[rjack321]

True but the modern scientific recommendation ultimately comes out to be the same prolonged shallow stops that got a lot of guys like JJ and GI3 bent. This is why some of these old school DIR people like AG would say that even before Navy studies were done, we already did that pure Buhlmann shallow stop which is being propagated now and we have gotten skin bends so no thanks. Keep your science to yourself we want to be safe. Been there, done that and gotten bent! GI3 is talking exactly when he talks about skin bends and those other symptoms. .

I'd say (and @kensuf 's comment) supports this, they were experimenting as they went. Maybe they got bent less bad or it was the luck of the draw that adding deep stop time to something like a Bill Hamilton table (which is hard to even find nowadays) was actually better. I think saying they were doing buhlmann along the lines of how shearwater (nowadays) has implemented Buhlmann would be a stretch. Good computers really didn't exist back then. Even with my entry in 2003ish the available choices were a UWATEC 330m bottom timer + decoplanner & RD, or you had something like the Nitek He from diverite which was really an awful wrist computer. IIRC Suunto didn't even have a model that supported helium at that time. If I had a black and white choice between RD and a Nitek He today I'd probably lean towards RD honestly.

 

[Dan_P]

Why? How? If on- and off-gassing are affected the same way, how would that favor shallow stopping instead of just increasing the time required?

Hypothermia's effect on decompression is not mapped out, but let's say - for argument's sake - you have 70 minutes of decompression at 100% capacity, then it drops to 0% after 70 minutes. That's obviously not a likely illustration of how hypothermia works, but humour me;

If you have 70 minutes of decompression you can do before hypothermia (in this case) reduces decompression so greatly that it doesn't make sense to do it at all, we'll look at where divers A and B are at that point in time. e.g.:
A is at 15m, B is at 6m at that time.
Who will have gotten the better deal?

Thus, hypothermia may well impose a significant disadvantage to deep stopping divers.

 

[rjack321]

Hypothermia's effect on decompression is not mapped out, but let's say - for argument's sake - you have 70 minutes of decompression at 100% capacity, then it drops to 0% after 70 minutes. That's obviously not a likely illustration of how hypothermia works, but humour me;

If you have 70 minutes of decompression you can do before hypothermia (in this case) reduces decompression so greatly that it doesn't make sense to do it at all, we'll look at where divers A and B are at that point in time. e.g.:
A is at 15m, B is at 6m at that time.
Who will have gotten the better deal?

Thus, hypothermia may well impose a significant disadvantage to deep stopping divers.

The irony being that for at least a decade the "conventional wisdom" regarding abbreviated deco was to do all the deep stops and skip the shallow stuff. AKA protect those fast tissues with all those deep stops, the slow ones at least wont be type II DCS....

Oh how wrong that was.

 

[Dan_P]

In the flooded suit-scenario, I'm preoccupied with fractions of inert gas.
Spending as much time as I can tolerate on O2 prior to ascend would be my goal.