How long before flying?

[RainPilot]

The GF will affect how long you stay in the water etc, the base formulae for Buhlmann will be a reflection of actual inert loading (like the SW GF99 display). The desat is when your loading is low enough that subsequent dives aren't considered to be repetitive dives. I imagine there is a correlation with safety to fly but no-one is going to print that in their manual...

I am always wrong about everything but I believe that the Oceanic etc etc all use specific combinations of compartments whereas the Buhlmann will be using all 16, some of those compartments have really long half lives. Maybe that's where the longer desat time comes from?


Some resources:

The Ten Foot Stop: Flying/Going to Altitude After Diving, Diving At Altitude

 

[scubadada]

The GF will affect how long you stay in the water etc, the base formulae for Buhlmann will be a reflection of actual inert loading (like the SW GF99 display). The desat is when your loading is low enough that subsequent dives aren't considered to be repetitive dives. I imagine there is a correlation with safety to fly but no-one is going to print that in their manual...

I am always wrong about everything but I believe that the Oceanic etc etc all use specific combinations of compartments whereas the Buhlmann will be using all 16, some of those compartments have really long half lives. Maybe that's where the longer desat time comes from?

Thanks. Native Buhlmann is not that much different than DSAT. I like your idea that different compartments may be utilized in the desat calculation, it may even be correct

 

[RainPilot]

Thanks. Native Buhlmann is not that much different than DSAT. I like your idea that different compartments may be utilized in the desat calculation, it may even be correct

Them's fighting words....

Seems like the DSAT method is more liberal than a straight Buhlmann implementation so it makes sense that the desat would be quicker as well.

 

[RainPilot]

I have a big dog in this fight, as an operational pilot who likes to dive, juggling diving and no fly times is ...interesting. I've done EAN50 dives on a 30'/10m dive because I was on standby 6 hours later. I have the luxury of setting cabin altitude to whatever I like, I also have O2 I can prebreathe before takeoff but still, its all guesswork.

Would love to hear @Dr Simon Mitchell or @Duke Dive Medicine or @debersole take on this.

 

[scubadada]

Them's fighting words....

View attachment 399098

Seems like the DSAT method is more liberal than a straight Buhlmann implementation so it makes sense that the desat would be quicker as well.

PZ+ is not native Buhlmann, it is a proprietary, detuned, version that runs somewhere around a GF hi of 85 or so. DSAT runs somewhere around a GF hi of 95. These values are not perfect, there are some other variables. I've run my last 100 dives with my VT3 (DSAT) and my Nitek Q (ZH-L16C), mainly to get experience with Buhlmann.

As before, the Q consistently has considerably longer desat values than the VT3. I would also like to hear what other folks have to say. I find the entire topic fascinating

 

[scubadada]

I will contact Oceanic and obtain more details regarding their calculation of desat time while using DSAT. I will do the same with Dive Rite, however, they really do not support the computer and have been unresponsive to my previous requests. I have had better luck with DGX and will try them too.

 

[boulderjohn]

I like, I also have O2 I can prebreathe before takeoff but still, its all guesswork.

NOAA used to have ascent to altitude tables published on their web site. If they are still there on the newly designed site, I can't find them. They gave recommendations for ascending to altitude (driving, hiking, or flying) based on your ending pressure in the NOAA tables, which I believe were the same as the old Navy tables. Dr. William Clem, the hyperbaric medicine doctor in Denver, Colorado, once provided guidelines for breathing oxygen after diving and before ascending, telling how breathing oxygen would change your pressure group on the NOAA tables. I provided those details in this thread in posts #2 and #5.

He provided this information because so many Denver-area divers dive in Santa Rosa, N, and return the same day to the Denver area, which necessitates a number of altitude changes. I am one of those divers. I may be making that drive shortly after doing a deep decompression dive, and I have done that often. When I do, I usually finish off my oxygen deco bottle, first while breathing it for a while on the surface and then by breathing it while I am driving. I stop when the bottle is empty. By taking long inhales, and letting the O2 linger on the lungs a while, I can make it last a long time.

 

[tursiops]

NOAA used to have ascent to altitude tables published on their web site. If they are still there on the newly designed site, I can't find them. They gave recommendations for ascending to altitude (driving, hiking, or flying) based on your ending pressure in the NOAA tables, which I believe were the same as the old Navy tables.

The most recent tables are Table 9-6 in the Rev 7 USN Diving Manual. There, the longest wait-time after an NDL dive before flying in a commercial aircraft is 21:01h.
For "Exceptional Exposure" dives (most deco dives), wait-time is 48h.

 

[scubadada]

I will contact Oceanic and obtain more details regarding their calculation of desat time while using DSAT. I will do the same with Dive Rite, however, they really do not support the computer and have been unresponsive to my previous requests. I have had better luck with DGX and will try them too.

I heard back from AUP, DGX and Dive Rite yesterday. For both Oceanic DSAT computers and the Dive Rite Nitek Q running Buhlmann ZH-L16C, desaturation time is the amount of time that must pass before the residual nitrogen levels drop to a point where subsequent dives are treated as single (non-repetitive) dives. Both say they use all tissue compartments. Buhlmann does have a longer half life compartment than DSAT, 635 vs, 480 minutes, I don't know that this is the explanation for the differences in desaturation time between my 2 computers.

I have an upcoming trip to Cocos where I will be doing extensive daily diving. I will record the desaturation times during the week of diving to better illustrate my observation.

I do not use the desaturation times for any decision making and generally follow the DAN flying after diving recommendations. I would still be interested in hearing what folks with more knowledge and experience have to say on this topic.

 

[ReefHound]

18 hours before flying may not be enough!
Alert Diver | Flying After Diving

Thoughts?

Yeah. Since they conducted in-flight bubble tests for divers after waiting 24 hours, why not also test after 18 hours since that is a commonly recognized minimum for repetitive no-violation diving?

And how do they draw the conclusion that 24 hours is probably safe but 18 hours needs another look when 24 hours produced bubbles and 18 hours wasn't tested? How do we know that 18 hours would have produced any more bubbles than 24 hours? How do we know that 48 hours wouldn't have produced bubbles in some? For all we know, even some non-divers produce bubbles when flying.