Dear Readers, (as our very own Doc Deco would say),
This topic has aroused an amazing amount of controversy and no little heat, some of which is mine, I must admit. To return to point, so to speak, I would like to take the liberty of re-posting some very pertinent remarks by the good Doctor. (Also to apologize for what, of necessity, will be a rather long post!)
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Microbubbles in the Cabin
Dear Readers:
Flying after diving
This is a problem not yet solved except in a very general way. Divers can tell this because, while dive depths and times are very closely regulated, the time-to-fly duration is more or less just a general rule of thumb.
Considerable research has gone into the development of dive tables. This same degree of testing has not gone into dive/fly rules. This is most likely because government agencies (e.g., US Navy) are the biggest providers of money and they do not dive and fly. When a question such as this arose at NASA, we had a very specific protocol in mind and tested only that protocol. Scuba diver schedules are a varied mixture. Unless a dive computer maker would wish to test this, little will probably be done - - EXCEPT FOR THE DAN STUDY. (Emphasis mine.--Ed.)
Bubble Growth
If you wish to determine if a preformed gas phase exists in a liquid (or tissue), the easiest way to do this is to depressurize it and look for visible gas bubbles. All decompression bubbles in water or tissue start from preformed bubbles. These are termed the nuclei (by EN Harvey in the 1940s).
When one goes from sea level to altitude in an airplane, DCS can only result if the preformed nuclei are larger than a certain size, and in sufficient number, that pain will result. An ascent to 8,000 feet (cabin altitude) would require micronuclei of several microns in size (to overcome the surface tension = Laplace pressure). These are not present in sufficient number in the ordinary passenger to cause problems. This is obvious because people do not get the bends from riding in a commercial aircraft cabin.
Diving and Bubble Growth
If you are a diver, however, and board an airplane with residual bubbles from diving , you may indeed have a sufficient number of microbubbles larger than the Laplace limit. When going to altitude, they WILL grow.
When you go diving again, these will shrink, and they can be controlled to some degree. You do not have the luxury of compression prior to flight.
Emergency Depressurization
This was something I looked into for the FAA. Generally, DCS will not be a problem within a realistic time-frame up to about 40,000 feet of altitude for the ordinary passenger. If you are bringing back nuclei as a souvenir of your dive trip, you might get an unexpected problem. This type of a depressurization is not common, but sometimes there are failures of the cabin pressurization systems.
Dr Deco
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These are all excellent points from a man who has the education and research to back them up, and who's job it is to study this stuff for our very own space agency. This leads, inescapably, to several conclusions:
(1) The DAN study is the only on-going study of its type, and, alas, the final results are not yet published.
(2) The various FAD tables and recommendations, such as NOAA, DAN, PADI, NAUI, et al, are extrapolations based upon current knowledge and decompression algorithms, most of which rely upon SYMMETRICAL on and off gassing. As much new research is beginning to show, however, this is not likely to be so in vivo.
(3) Until the DAN study is published, based or modeled on actual experimental results, we cannot KNOW for certain.
Until that time, however, I can make certain judgements from the standpoint of my job.
(1) I am paid to get the airplane, its passengers, and the cargo SAFELY to the scheduled destination. After many years on the job, and many, many tests in the "Sim", I can state with pride that I do my job extremely well.
(2) Any medical emergency aboard my aircraft, especially one that requires a diversion to another destination, throws a lot of sudden variables into the established plan. This invariably raises risk factors, and I (and every other professsional pilot) do NOT like this. I will get us all there safely, but it will cost a lot in terms of money, time, and aggravation.
(3) If this emergency is not of your making, neither I or anyone else will begrudge the time, and money it takes to help you!
(4) If you have caused this emergency by your own willful disregard for proper procedure, and/or behavior, my company, the NTSB (National Transportation Safety Board), and various legal staffs will be involved in examining your situation. If it is determined that you acted willfully, and with disregard for what is known to be established safe procedure, they WILL take you to court to recover the VERY SUBSTANTIAL COSTS.
I have to admit that, since I am an instructor for IANTD, I believe in the often stated philosophy of our founder, Tom Mount. He believes that, once informed of the risks, we all have a right to risk ourselves as we see fit. I say again, I DO believe that.
If you wish to risk yourself and your health by flaunting known and conservative procedure by climbing out of the water from deco dives and flying with your hair still wet, have at it brother!=-)
As a piece of sincere advice, DO NOT tell me about it! DO NOT tell others about it! Above all, DO NOT put it in print.
If you do, I will be the one to testify to all of the above named agencies that you risked all of us on the airplane WILLFULLY AND KNOWINGLY!!! That, sir, is my job!:box:
