No fly time off gassing rate

[boulderjohn]

there are guidlines that range from 2 hours to 48 depending on the dives and the flight.

Are you referring to the NOAA table? That does give shorter duration guidelines based upon your ending pressure group on the U.S. Navy tables, which I am guessing the OP might not be using. In addition, that table is based on climbing to altitude by means other than an airplane. For airplane travel, it says to wait 48 hours.

If you have another resource, I would be very interested in a specific identification.

Mala and I had an interesting discussion via PM. It led to an investigation that I will summarize.

In his post, he was referencing something he found online on an individual's web site: a table for ascent to altitude that was (in both our views) very liberal in how little time it required before flight after short dives. It was described as a 1989 table for commercial divers created by UHMS. In my research, I found that in 1989 UHMS published guidelines for flying after recreational diving that were more conservative than the current DAN guidelines. I learned that those guidelines were controversial and led to a conference with DAN that produced new DAN guidelines in 1991. I was able to find those 1989 recreational guidelines in a number of sources, including the abstract of the original UHMS publication.

I was not, however, able to find any other source for the supposed 1989 table for commercial divers. This table was liberal in that it allowed for flying relatively soon if the diver had not been under pressure for more than 60 minutes in the previous 12 hours, but its recommendations were otherwise more conservative than the DAN recommendations. The 2 hour wait time mentioned by Mala is actually for an ascent to a pressure of 2000 feet or less. That is actually more conservative than the DAN guidelines, which require no wait at all for such an ascent.

 

[mdax]

The noaa table is what I'd use. It says to use 8000' for commercial aircraft, which I'd use based on this paper discussing that the FAA sets a rule of no more than 8000' for passenger aircraft.
I believe the proper table for determining the designation groups used in the previously linked table is here

 

[Mr Carcharodon]

You have v-planner? Try this. Set your starting altitude to 8000 feet (or 2440 m) which is cabin pressure for commercial flights. Dive to 9 feet for 48 hours, that will re-set your tissue pressures to sea level. Then put in your planned dive, but always return to 9 fsw as the last step in your dive. V-planner will then calculate how long you have to wait to return to a 8000 foot altitude which is your no fly time.

So for example if the ocean started at 8000 foot altitude and you dove to a depth of 9 feet your ambient pressure would be 1 atmosphere. If you dove to 33+9 fsw=42 fsw you would at 2 atmopheres...and so on.

 

[Tigerman]

I think theres atleast one problem with the vplanner approach and thats ascent rates. An airplane probably "ascends" a lot faster to the 4500-8000 ft cabin pressure than when you dive?
(The cabin pressure varies with the airplanes altitude and between models)

 

[Mr Carcharodon]

Really? Do you think most airplanes ascend to 8000 feet in less than 20 seconds? There is the same pressure difference between 8.5 fsw and the surface as there is between the surface and 8000 feet altitude. Pressure changes during flying are slower because air is a lot less dense than water.

In any case it ascent rates are pretty irrelevant since fast compartment offgassing rates are not going to drive no fly time.

 

[GrumpyOldGuy]

Are you referring to the NOAA table? That does give shorter duration guidelines based upon your ending pressure group on the U.S. Navy tables, which I am guessing the OP might not be using. In addition, that table is based on climbing to altitude by means other than an airplane. For airplane travel, it says to wait 48 hours.

If you have another resource, I would be very interested in a specific identification.

Could you cite your source on the 48 hours for airplane travel? It's new to me and would like to read it.

I have used the NOAA tables below, from the NOAA site and they specify using 8000' for airplane travel and don't mention anything about 48 hours.

I don't think I would use these to push for same day flights, but I do use them when close to the 18 hour limit and want to see how close I am to the fuzzy line.

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

 

[gurnie]

The wife works in an ER and she has seen more than once divers on vacation down in Mexico who dive that morning and take a flight that night. Give it 24 hours, it is not worth a stay in a chamber... Your friends are going to be shallow, just snorkel above them...

 

[boulderjohn]

Could you cite your source on the 48 hours for airplane travel? It's new to me and would like to read it.

I have used the NOAA tables below, from the NOAA site and they specify using 8000' for airplane travel and don't mention anything about 48 hours.
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Yes, they do.

Go all the way to the bottom of the table and then read the first sentence after it.

 

[GrumpyOldGuy]

Yes, they do.

Go all the way to the bottom of the table and then read the first sentence after it.

You mean the note below the Z group where is says "Exceptional Exposure Wait 48 hours before flying"?

I believe that is referring to when you have exceeded the Z group (E.G. Hit deco), not a general limit.

If it was a general limit, they would not have the note about use 8000' for altitude for commercial flights.

 

[boulderjohn]

You mean the note below the Z group where is says "Exceptional Exposure Wait 48 hours before flying"?

I believe that is referring to when you have exceeded the Z group (E.G. Hit deco), not a general limit.

If it was a general limit, they would not have the note about use 8000' for altitude for commercial flights.

You may be right. I frankly never paid much attention to it.