Why the wait to fly?

[MtnDiverColorado]

Hello, I was watching the Mbars change on my Teric on the plane on the way home from my last dive vacation, and have a question...

The pressure change, according to my Teric when I am flying goes from ~1K Mbars, to about 800... That change takes a while to happen on the plane, as pressure slowly drops after take off, but I am told I should wait 24 hours after diving to endure that slow 200 Mbar drop...

Yet, when I dive, and am at 33 ft, I am at ~2000 Mbar. If it takes me 8 mins to get to the top, with a 5 min safety stop, that is seen as a very safe ascent.

So my question is, is there something about that 200 Mbar change on a plane that is more problematic than the 1000 Mbar change diving? or is the flight recommendation just very conservative, or am I being dumb and my reasoning is off....

Just something I was thinking about... thanks for any insight..

 

[PR_SMITH]

If the plane were to lose cabin pressure at altitude, there is potential to get bent.

 

[tursiops]

The fact that you can surface at sea level and (usually) avoid DCS is because the algorithms/tables are designed for going to sea level. You still ahe an overpressure in yoru tissues, but not so much that it comes out at 1000mb. If, instead, you go to 800mb then the overpressure in your tissues is too much and it comes out as bubbles and you get bent. Why so long? Because the gas comes out of the tissues slower and slower (at a safe rate) as you have less and less pressure difference between your tissues and your ambient pressure.
Worse, if the cabin should lose pressure, you are REALLY in trouble.

 

[JohnN]

Hello, I was watching the Mbars change on my Teric on the plane on the way home from my last dive vacation, and have a question...

The pressure change, according to my Teric when I am flying goes from ~1K Mbars, to about 800... That change takes a while to happen on the plane, as pressure slowly drops after take off, but I am told I should wait 24 hours after diving to endure that slow 200 Mbar drop...

Yet, when I dive, and am at 33 ft, I am at ~2000 Mbar. If it takes me 8 mins to get to the top, with a 5 min safety stop, that is seen as a very safe ascent.

So my question is, is there something about that 200 Mbar change on a plane that is more problematic than the 1000 Mbar change diving? or is the flight recommendation just very conservative, or am I being dumb and my reasoning is off....

Just something I was thinking about... thanks for any insight..

24 hours before flying is now considered a bit too conservative.

Even PADI is saying:

 Flying after Diving Recommendations For Dives within the No-Decompression Limits

• Single Dives: A minimum preflight surface interval of 12 hours is suggested.
• Repetitive Dives and/or Multi-Day Dives: A minimum preflight surface interval of 18 hours is suggested.
• For Dives requiring decompression stops: A minimum preflight surface interval of greater than 18 hours is suggested.

https://kentico.portoflosangeles.org/getmedia/c2ba110c-7e0d-411a-8141-309d7e9ba781/diving-after-flying-(10-2019)_12272019_01012020_#:~:text=PADI%20%E2%80%A2%20Flying%20after%20Diving,Dives%20requiring%20decompression%20stops%3A%20A

 

[tursiops]

See https://scubaboard.com/community/resources/flying-after-diving-dan-workshop-report-2002.19/ if you want all the details.

 

[arew+4]

24 hours before flying is now considered a bit too conservative.

Even PADI is saying:

 Flying after Diving Recommendations For Dives within the No-Decompression Limits

• Single Dives: A minimum preflight surface interval of 12 hours is suggested.
• Repetitive Dives and/or Multi-Day Dives: A minimum preflight surface interval of 18 hours is suggested.
• For Dives requiring decompression stops: A minimum preflight surface interval of greater than 18 hours is suggested.

https://kentico.portoflosangeles.org/getmedia/c2ba110c-7e0d-411a-8141-309d7e9ba781/diving-after-flying-(10-2019)_12272019_01012020_#:~:text=PADI%20%E2%80%A2%20Flying%20after%20Diving,Dives%20requiring%20decompression%20stops%3A%20A

Maybe a little more than needed, but better safe than sorry, beside you ought to spend some time at your destination above the waves.

 

[inquis]

The rate at which ambient pressure drops is not the issue. It's the level to which it drops that can create problems.

 

[tursiops]

The rate at which ambient pressure drops is not the issue. It's the level to which it drops that can create problems.

Well, sort of. However, if the rate were very slow -- such that the off-gassing can keep up with it -- then there would be no problems. Example: if the plane takes 18h to reach altitude, you can probably. board it right after your dive!

 

[Kendall Raine]

The rate at which ambient pressure drops is not the issue. It's the level to which it drops that can create problems.

Going to altitude is analogous to ascent rate and ascent rate matters.

 

[Green Frog]

OK, let’s do a practical calculation. Let’s say I’m planning on a lovely trip to the Bahamas. I would be diving for 3 days, doing AM & PM 2 tank dives each day, for a total of 12 dives. Assuming I’m out of the water by about 3:30-4:00 on the third day, and that I’ve followed conservative, no deco dives to 80-90 ft max for all three days, can I assume I’ll be safe to fly early the following afternoon, or is my accumulated N2 load sufficient that I should wait a full 24 hours (or more) by the clock? Reading this thread makes me think an earlier flight should be fine, but what think ye?