Do you/would you fly with an 19hr surface interval?

[Thalassamania]

How does that effect the time-to-fly limitations?

I don't think cascas understands decompression theory. Ascent rates have nothing to do with the question at hand.

Tech dives have much longer bottom times at higher pressures, resulting in a more nitrogen loading, especially the slower tissue compartments. The time to off-gas those slow compartments is correspondingly longer.

The bet was over someone who was doing repetitive dives to 250 feet and then flying. Tech has the advantage of decoing on 100% O2, which is what he did. It has nothing to do with ascent rates. He was able to off-gas enough on 100% O2 to keep himself from getting bent when he got on the plane.

As Billy-Bob used to say, when he was still with us, "Green gas is good gas."

I think that's the real reason. Even I, neophyte that I am, have noticed my computer tells me a much shorter "no fly" time after a tec dive decompressing on pure O2 (usually circa 14 hours) than it does after a non-decompression dive with a standard safety stop (usually circa 19 hours).

Even that is likely wildly conservative. The old guideline was USN Repetitive Dive Group D in order to fly. USN Repetitive Dive Group D was a flawed guideline because a diver who had just entered D was safe to fly, but a D diver about to enter E was not. So we cut it back to USN Repetitive Dive Group C. If you have any decompression planning software, play with it ... you'll be amazed at what a great tool pure oxygen is, especially when delivered in the water at a shallow stop.

 

[Mr Carcharodon]

you'll be amazed at what a great tool pure oxygen is, especially when delivered in the water at a shallow stop.

Is there any decompression model that really does this? Certainly dissolved gas models do not. The bubbles models that include Boyle's law get closer, but even the it does not appear to work. It seems the oxygen window is a potentially fruitful area to work on.

Certainly if you take Buhlmann's model on it's face value you would conclude that the DAN guidelines make no sense. You just cannot say that Buhlmann is right, and DAN is right. Personally I would like to hear about what DAN did to screen out false positives. It appears very little which does not seem to be a sound basis for policy.

 

[XS-NRG]

So a no-fly time of less than 24 hours is now the same as drunk driving? Seriously?

I think you need to ask yourself if you are serious about what you just said. Obviously the answer to your question is no, it's an analogy about waiting only a minimum amount of time. The point has clearly been lost and I'm not prepared to play games now.

 

[kolmogorov]

To throw in another data point, I recently made a symptom-free ascent to 10,000 feet after a ~17.5-hour "no fly" time, following 2 dives on air to max. 130 and 70 feet, respectively, average depth was under 50 feet and duration about 40 min. in both dives, s.i. about 40 hours before the first and 80 min. before the second dive, generous safety stops and a slow last 15 feet. The ascent to altitude took 2 hours, with about a 25-minute break at somewhere about 3500..4000 feet. I drank >3 liters to hydrate in the hours before and during the ascent. I did it with the feeling that it was risky, and unfortunately I would probably do it again, although not after reading up a little more on the subject and studying the actual science behind it. In this thread below a couple of folks have offered what appear to be useful pointers...

http://www.scubaboard.com/forums/ba...ged-decompression-tables-ascent-altitude.html

 

[scubadada]

USN/NOAA dive tables return you to dive group A at 12 hours. DAN recomendations of 18 hours seem reasonably conservative for most situations. I consider the 18 hours a minimum and attempt to have more time if available to me. I do pay attention to my computer desaturation countdown and try to take it into consideration when possible. I have had desat times greater than 18 or 24 hours on occassion.

Good diving, Craig

 

[DiveNav]

......18 hour UW in 3 days is fairly intense. I'd suggest taking a look at divePAL and see if it will simulate your planned dives and off-gassing status for your planned flight. .....

Hi,
I finally got around entering into divePAL a plan similar to the one mentioned by the OP: basically I made 12 identical dives over a 3 days period : each dive has a square profile (30ft/90min).

I then analyzed the whole sequence with divePAL in Moderate settings. (for more info on our algorithm read the article Fine Tuning a Decompression Algorithm)

As per image below, at the end of the last dive the Nitrogen Loading is 76% and the Estimated Pressure Group is S.

​

Also, at the end of the 19 hours of Surface Interval after dive 12, the Nitrogen Loading is 10% but the Estimated Pressure Group shows DESAT. See image below.

​

This plan is public on divePAL server; just search dive logs for "ediver / dive plan".
To analyze the whole sequence you will need the Tech version.

10% is more than 0%

Alberto (aka eDiver)

 

[FPDocMatt]

+ 1 on using Nitrox, skip the last dive and sit on the beach and have a beer

It's amazing, the original post is pretty much what I'm planning to do next week, except that I'm planning to dive with EAN32. And my flight is exactly 19 hours after my last dive. But my depths will probably be a bit more than 30 feet. I'll be at the Amoray Dive Resort on Key Largo for 2 days of diving -- 4 dives day 1, 2 dives in the morning of day 2. Then flying out the third day.

 

[Danseur]

There are a lot of great suggestions in this thread on how to mitigate your risk. Ascent rate is the most critical of all the factors here. HANG out at 20 feet for a while at the end of your dives, and SLOWLY ascend from there.

How deep?

 

[FPDocMatt]

There are a lot of great suggestions in this thread on how to mitigate your risk. Ascent rate is the most critical of all the factors here. HANG out at 20 feet for a while at the end of your dives, and SLOWLY ascend from there.

Great suggestion! During the Cozumel Invasion several of the people in my group liked to spend 4 or even 5 minutes at the 15-foot safety stop, and one person said he likes to always stop 1/2 way from his max depth as well. (I think that's called a deepstop?) Another diver has a computer with red, yellow and green areas. Yellow is acceptable, but he likes to wait until he's in the green before ascending from his safety stop. My computer just tells me how much longer I can stay at my current depth.

The thing about stops, though, is that you're taking on nitrogen. Off-gassing is quicker at the surface, but the quicker you ascend the more likely bubbles will form. You could stay at 15 feet for 15 minutes, but then wouldn't your surface interval have to be longer before the next dive?

How deep?

I don't know, I'm just going to get on the boat when they go out each day, and see where they take us.

 

[Insta-Gator]

Each to their own trickery. But for me, one last dive within the 24 hour window is not worth the potential health risks. There's always the next trip for another dive.