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

[cascas]

I lost a $50 bet on DecoStop with a guy who wanted to fly 12 to 15 hours after technical deco dives. He flew, didn't get bent, and I lost $50.

Technical Deco dives usually have much slower ascents, especially in the last 6 meters. These are not really comparable with rec dives. You lost fair and square...

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[John_B]

Now, I have only read half of the responses here so maybe I missed it but if the airline is competent and knows anything about diving and they find out you've been diving through casual conversation you could find yourself being refused on the plane. This happened to me 3 years ago. I was in Australia and dove the Whitsundays (discover dives as I was not certified yet) and had to take a take a flight a couple days later to head south and the cute flight attendant was asking me about my trip and what I got up to and once I told her I just finished diving she got extremely serious with me and demanded to know how long it had been since I last dove. I told her a couple days and then she relaxed and the flirting continued but I then asked her what she would have said or done if I had dove that day or within 24 hours and she told me she wouldn't let me on the plane if that were the case.

You know, I think that's exactly the point of this thread. People bristle at the idea of some uninformed bureaucrat implementing hard-and-fast rules based on what are actually guidelines (with God-only-knows how much padding built in to the figures).

 

[redacted]

Technical Deco dives usually have much slower ascents, especially in the last 6 meters. These are not really comparable with rec dives. You lost fair and square...

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

 

[XS-NRG]

On what basis do you decide to wait 24 hours? Why not make it 36 or 48 and be extra extra safe? I'll fly 18 hours after diving and I won't mention it to the airline. You can go somewhere like Bonaire where the weekly Saturday flight out leaves between 7:00 - 8:00 AM and I suspect 25% or more the plane has dived within the last 24 hours.

You know you could make it 36 or 48 or a week if you wanted to. Without getting into debating peoples preferences for conservatism and their right to free will and choice I think that one could be pushing it by waiting the minimum and then doing something somewhat cavalier. If anyone thinks this is not cavalier and is assumed to be acceptable then could I also assume that if the legal limit to drive is 0.08 (blood alcohol) are you going to stand at the door of a bar and blow into the box until you hit 0.079 then say "I'm under the limit now, let's go". Even though you have reached a minimum and are "legal" does that necessarily mean you "should" hop into a car and drive? Physiologically we are all different and one person may be fine to fly after 6 hours and drive at 0.1 while the next has to wait more than 24 hours and is too drunk at 0.04. Where do we draw the line? My point is you shouldn't consider only yourself. There are other factors to consider and other people involved (emergency landing vs an innocent bystander being killed when crossing the road). Something to think about... :cool2:

 

[diverrex]

You know you could make it 36 or 48 or a week if you wanted to. Without getting into debating peoples preferences for conservatism and their right to free will and choice I think that one could be pushing it by waiting the minimum and then doing something somewhat cavalier. If anyone thinks this is not cavalier and is assumed to be acceptable then could I also assume that if the legal limit to drive is 0.08 (blood alcohol) are you going to stand at the door of a bar and blow into the box until you hit 0.079 then say "I'm under the limit now, let's go". Even though you have reached a minimum and are "legal" does that necessarily mean you "should" hop into a car and drive? Physiologically we are all different and one person may be fine to fly after 6 hours and drive at 0.1 while the next has to wait more than 24 hours and is too drunk at 0.04. Where do we draw the line? My point is you shouldn't consider only yourself. There are other factors to consider and other people involved (emergency landing vs an innocent bystander being killed when crossing the road). Something to think about... :cool2:

But the point is it is not done cavalierly. It is done with research and consideration of a wide range of factors. Blindly following some arbitrary rule such as "24 hours" is cavalier.

http://www.ndc.noaa.gov/dp_forms.html

 

[Rickelpickel]

You know you could make it 36 or 48 or a week if you wanted to. Without getting into debating peoples preferences for conservatism and their right to free will and choice I think that one could be pushing it by waiting the minimum and then doing something somewhat cavalier. If anyone thinks this is not cavalier and is assumed to be acceptable then could I also assume that if the legal limit to drive is 0.08 (blood alcohol) are you going to stand at the door of a bar and blow into the box until you hit 0.079 then say "I'm under the limit now, let's go". Even though you have reached a minimum and are "legal" does that necessarily mean you "should" hop into a car and drive? Physiologically we are all different and one person may be fine to fly after 6 hours and drive at 0.1 while the next has to wait more than 24 hours and is too drunk at 0.04. Where do we draw the line? My point is you shouldn't consider only yourself. There are other factors to consider and other people involved (emergency landing vs an innocent bystander being killed when crossing the road). Something to think about... :cool2:

Well said, XS-NRG

"DCS is not always avoidable", that being said, there is still a lot we're learning about the effects nitrogen on our tissues and body. The "rules" are just "conservative safe guidelines" implemented for "the average "recreational" diver.

Edit: The only way to 100% avoid the risk of DCS is "not to dive"..

 

[Doc Harry]

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.

 

[John_B]

You know you could make it 36 or 48 or a week if you wanted to. Without getting into debating peoples preferences for conservatism and their right to free will and choice I think that one could be pushing it by waiting the minimum and then doing something somewhat cavalier. If anyone thinks this is not cavalier and is assumed to be acceptable then could I also assume that if the legal limit to drive is 0.08 (blood alcohol) are you going to stand at the door of a bar and blow into the box until you hit 0.079 then say "I'm under the limit now, let's go". Even though you have reached a minimum and are "legal" does that necessarily mean you "should" hop into a car and drive? Physiologically we are all different and one person may be fine to fly after 6 hours and drive at 0.1 while the next has to wait more than 24 hours and is too drunk at 0.04. Where do we draw the line? My point is you shouldn't consider only yourself. There are other factors to consider and other people involved (emergency landing vs an innocent bystander being killed when crossing the road). Something to think about... :cool2:

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

 

[Rhone Man]

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.

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).

 

[-hh]

I was under the impression that the body is off-gassing more efficiently at safety stops than at the surface.

I remember a chart....somewhere.... somehow... that scientists were using to track micro-bubbles. A bunch of different profiles were used including direct ascents. The '10m/min ascent with safety stop' profile showed less micro-bubbling than a 10m/min ascent direct to the surface.

This would tell me that 5mins at a safety stop would be 'worth' more than 5 mins at the surface.

In principle, the largest 'tolerable' gradient is what will be most effective at having the gas transfer occur...think of it like Potential Energy. This is the same as what we observe when we compress (dive) for ongassing; its just that we can't decompress as "strongly" without the risk of DCS.

However...and this is where the tracking of microbubbles comes in...what research has found is that we will get tiny bubbles in our bloodstream which, for as far as we can determine, aren't "harmful", and the traditional tables/models which permit getting to the surface relatively quickly for the "Strongest Tolerable" gradient didn't know that they were permitting microbubbling.

However, what has also been found is that once a bubble has formed, the gas transfer becomes less effective, which means that the offgassing is slower and not optimized.

As such, we need to refine what we want: what we want is the optimal pressure gradient at which the transfer rate is the highest (without harm), and based on current knowledge, we want this pressure to be just before microbubble formation starts.

For a given dive profile, let's assume that this point is at 13.7 ft, which is why a 15ft safety stop is a good thing. However, after X minutes at that stop, the diver has been successful in reduding his N2 loading .. which means that the "optimal pressure" point has changed and needs to be recalculated. Because there's now less residual N2, the optimal point is going to be shallower ... and it is eventually going to be at the surface. (Actually, in theory, it will continue to drop even below 14.7psia of sea level).

The pragmatic question is going to be how long of a Safety Stop is going to 'speed up' offgassing and what's the magnitude of the benefit? I can't recall any models that really try to model/track microbubble formation to allow a longer repetitive dive because your prior dive's ascent was confirmed to be good - - sure, there's dive computers (like Suunto) that will punish a diver for a skipped safety stop, but what's not clear to me is how well grounded this is in quantitative science ... I suspect that such examples are just very crudely rule-based (ie, "he only made a 2:59 stop, so he failed to clear the 3:00 flag, so multiply all of his M-values by XX constant).

Saying that- with the described profiles of the OP, safety stops would do little effect as the long compartments are controlling the dive for which incredibly long safety stops are needed to do anything significant.

Agreed, although a 5 minute stop at 6ft (2m) still wouldn't be a bad idea.


-hh