Why wait 12-24 hrs to fly?

[vladimir]

Interesting timing of this thread. I was always of the understanding that the wait was 24 hours, until a year or two ago when I heard some agencies suggested 12 hours would be fine.

Here's my situation. Next Tuesday I'm scheduled to dive the Spiegal and Duane (90-100ft) in the morning, and a couple shallow reefs in the afternoon. I'm also considering a 1-tank night dive on a shallow reef (no deeper than 30-40 ft). My flight takes off the next day at 6:30pm. being that the night dive will likely end around 8:00 - 9:00pm on Tuesday, I will have no problem with that 12 wait; however, I will be short a couple hours on a 24 hour wait. The flight is not too long if that makes a difference (Tampa to Baltimore). I wish there was a dive shop in Key Largo that does a Monday night dive.


Steve

It makes a huge difference if you're writhing in excruciating pain the whole time. Otherwise, probably not.

The guideline for repetitive NDL dives is 18 hours, so you should be fine.

 

[drbill]

A few years ago we had a local instructor who was in the water doing basic training dives at shallow depths all well within NDL limits. After her dives, she drove across the island to be with her BF. The maximum elevation she reached was 1,600 ft, but she got bent and from what I have heard has never dived since then.

 

[TMHeimer]

CoopAir, Thanks for bringing this up. Other than you may be already bent before the flight or the cabin may depressurize, it is an interesting question. I've never thought of the figures you point out-- that you should never get bent under those circumstances. I guess there is something to it though, since people have gotten bent flying shortly after diving--the characteristics of air vs. water perhaps.

 

[Mr Carcharodon]

One difference in going to altitude is that you are unloading the slowest compartments which have the smallest allowables (m-values) and are generally only lightly loaded for recreational dives. DANs recomedation however does not match up very well with Buhlmann's deco model for most dives. But then most people are not going to sit at a computer and figure out how much the limits can be pushed. So we are left with simplified rules which nearly always work even if they are overly conservative sometimes.

 

[AfterDark]

one difference in going to altitude is that you are unloading the slowest compartments which have the smallest allowables (m-values) and are generally only lightly loaded for recreational dives. Dans recomedation however does not match up very well with buhlmann's deco model for most dives. but then most people are not going to sit at a computer and figure out how much the limits can be pushed. So we are left with simplified rules which nearly always work even if they are overly conservative sometimes.

bingo!

 

[supergaijin]

M-Values- the maximum tension ration that your body's various tissues can tolerate. These M-Values are typically set for sea level. Ascending to altitude may well exceed the maximum ratio your body can tolerate, causing bubbles to form, even hours after diving. Add cramped conditions, dry air etc.

Would setting your computer's conservative setting to altitude do much/anything for flying after diving?

 

[Edward3c]

The one thing I've not see discussed in this thread it the rate of climb commercial aircraft undertake. The change from sea level to fully pressurised only takes a few minutes and its totally outside the control of the diver.


I've known people get bent driving over reliantly low hills (under 2,000ft) after diving.

 

[theduckguru]

In the case of loss of cabin pressure, You can get bent flying at altitudes above 18,000 ft and never did a single scuba dive in your life.

 

[CoopAir]

Actually, in the event of a rapid decompression, you would go from 8000' to 35,000' in a few seconds. Thats the equiv of ascending at almost 150 feet per minute underwater (near the surface where the greatest PSI change happens to boot!)

On that note here is a scenario I've wondered about:

I do a 2 tank morning dive with the first one to 80 ft for 20 minutes then a 30 min SI and the second tank to 40 feet for 45 minutes and then 4 hours later fly back at just 1000 feet.

This would be in the Bahamas where I can fly low over the ocean in uncontrolled airspace. Itd be nice to have the flex to fly to another island 50 miles away and then fly back same afternoon as the wind direction sometimes dictates last minute changes as some island are best dove with a NE wind but others are better sheltered with the wind is from the south.

So is flying at just 1000' (plane not pressurized of course) 4 hrs after that dive profile too much risk? The utility would be nice.



---------- Post added February 26th, 2013 at 10:51 AM ----------

OK here is something else to consider....................

Lets say you are doing multiple dives over many days and you usually hit 80% of your NDL.....

If at the end of the trip you breathe pure O2 on the surface, how long do you have to do this to remove all residual N2 from your system??

And on that note, does it have to be an "on-demand" delivery to get the most out of it, or would breathing it from a hospital style mask give it to you efficiently enough?

If not an on-demand delivery system, how to you regulate the flow so its enough to breath from, but not so much that it overflows and is wasted?

 

[vladimir]

Actually, in the event of a rapid decompression, you would go from 8000' to 35,000' in a few seconds. Thats the equiv of ascending at almost 150 feet per minute underwater (near the surface where the greatest PSI change happens to boot!)

On that note here is a scenario I've wondered about:

I do a 2 tank morning dive with the first one to 80 ft for 20 minutes then a 30 min SI and the second tank to 40 feet for 45 minutes and then 4 hours later fly back at just 1000 feet.

This would be in the Bahamas where I can fly low over the ocean in uncontrolled airspace. Itd be nice to have the flex to fly to another island 50 miles away and then fly back same afternoon as the wind direction sometimes dictates last minute changes as some island are best dove with a NE wind but others are better sheltered with the wind is from the south.

So is flying at just 1000' (plane not pressurized of course) 4 hrs after that dive profile too much risk? The utility would be nice.

Consult the NOAA ascent-to-altitude table for the answer:

http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

It looks like a 3-hour interval is enough for an ascent to 1,000' if you emerge from your last dive as a K-diver or better.