Hi, I know the rule about not diving 24 hours before a flight, however, in Roatan, it was safe to dive in the morning before noon if leaving on a plane the following morning and it was a small 10 seater because the altitude wasn't too high.

I am most likely going to fly to Curacao when leaving and wondering if I can dive the day before - what is the general consensus on this?

Here is the latest from DAN

http://www.diversalertnetwork.org/medical/faq/faq.aspx?faqid=54

There is no general consensus.
People are all over the place on this topic.

But factually speaking, since I'm an engineer, what really matters is how high the a/c flies and how well pressurized it is. You can fly immediately after diving, per DAN, so long as you remain below 2000 feet equivalent altitude above sea level.

On a recent trip to Provo and Grand Turk, I took a hand held altimeter with me and measured cabin pressure on the 30 minute flight from Provo --> Grand Turk on a puddle hopper. It never exceeded 1000 feet inside the a/c.

So our last day on Grand Turk, we did two normal morning dives then grabbed a 3 PM flight back to Provo. We dove the next 4 days on Provo. We did NOT transfer to a big jet which would be pressurized to 8000 feet equivalent altitude.

Hope this adds to your confusion.

Regarding BON --> CUR, you are probably OK flying Divi Divi over there, but you still want to 24 hrs before getting on a full sized plane leaving CUR.

"There is no general consensus.
People are all over the place on this topic."

Tom, I guess I disagree. If people are not going along with the DAN recommendations (a consensus recommendation), they are playing with fire. You do still find folks who quote the old 12-h rule at you as a general practice in all situations, but they simply are not keeping up with how things have evolved. That old rule came from the Navy dive tables, long ago discarded.

The "24-h" rule does not exist; it is a conservative practice applied to the "at least 18-h" rule. I'm old, so I use 24-h, and try and make my last day not very deep, not very long, and high-percentage nitrox. But this is neither a rule nor the consensus...

Again I agree with Mel. I still like to stick with the 24 hour rule but can push it to 18+. Although I do not do any deco diving with my age I like to play safe. And that gives me time to play tourist anyway. I dive enough that playing tourist and shopper is hard to fit in during the week. I may do an early morning dive (transition dive or slightly later on Friday if I fly out Sat morning.

For instance on Bonaire the Saturday CO flight departs around 0730. I can fit in an early Friday morning dive and still have shopping time and off-gassing time of 24 hours.

Play it safe. It is for your own health and safety. This is what I tell my students as well.

Another thought as well. Don't think this rule is ONLY a flying rule. It is an ALTITUDE RULE. Should you be diving "locally" and have to drive over a high pass - WAIT just as you would for flying.

I know of cases (being currently in Ohio) of divers going to areas from North Carolina down to Florida. They get out of the water and start the drive back to Ohio for instance. That can involve altitudes of 3,000 feet and more. People have been bent doing this not realizing the risk.

I second Dan's message about driving mountain passes. In Puget Sound it isn't unusual to be able to dive and mountain ski in the same weekend. (It's one of the pleasures of living here, actually). Of course, you have to plan for them in the right order or else face the same risks as flying.

Christy, it's better to err on the safe side.

The "rules" are norms developed on average and median observations. Some people can fly 12 hrs after a dive, some may have to wait more than 24 hrs. Such individuals are outliers on a bell-curve. Most of us are right about the mean value and the rule of 18-24 hrs is a good standard.

In theory you can measure your tolerance to flying within a given number of hours after your last dive. But at the end of the day it may be better if you relaxed on your last day by snorkeling or exploring the dry side of Bonaire. The donkey shelter, for example, is a lovely place if you love animals.

If you want the non legal answer for yourself unless you plan on suing yourself - Depending on if you trust your dive computer. Depending on the depth and length of you dive will determine how many hours before it is safe to fly. As mentioned it is best to err on the safe side and make your last day on the island a land tour.

As for me I can do a 40 foot dive and be out of the water by 10 AM and fly out on the 7 AM plane the next morning. Since we are all built different, each and everyone should know their own capabilities.

Enjoy your Dive and Stay Safe

You should take a quick look at the tank at the hospital when you get to Bonaire. It might help you with your decision.

Fid - good point. I worked with the hyperbaric doc on Roatan over 10 years ago and did some research with his chamber (at Anthony's Key in Sandy Bay). Seeing what the lobster divers (the primary bent divers) suffered has made me so much extra cautious.

i had six rides in the chamber three years ago as a result of dwd (diving while dehydrated). never again. as i told the doctor at my last follow up, the treatment was as bad as the problem. fortunately, i had inner ear dcs and was cleared to dive in two weeks. still, i am very, very cautious now. the people who volunteer at the chamber are great...i can't say enough good things about them. but i'd rather see them at karel's or mona lisa than in the chamber.

Wow, there is some bad info being passed here!

The DAN 18-h consensus rule is not the mean or mode or median of a bell-shaped curve; all cases were looked at, and none needed more than 17-h. So the recommendation was set at 18-h. In Leo's language, that takes the tails into account. I'll provide a reference if anyone wants it.

Do NOT fly when your computer says OK, unless your computer is simply counting down 24-h. Some computers use "desaturation" as the time, and that is not long enough.

Mel, I would very much appreciate a reference. Thanks.

Here is the workshop report: https://www.diversalertnetwork.org/research/projects/fad/workshop/FADWorkshopProceedings.pdf
You have to be a DAN member to download it, but it can be purchased from DAN.

Some relevant quotes:

"The experimental design was based on a dive (or dives) followed by a PFSI (pre-flight surface interval) of three to 17
hours and a flight to 8,000 feet for four hours. We picked 8,000 feet because that was the
maximum airline cabin altitude that the FAA specified (4). The flights were four hours in
duration as our previous studies for NASA indicated that 92% of DCS occurred during
the first three hours of four-hour flights. Recreational divers were recruited as subjects." - page 32

"To choose the dive profiles, we used the Recreational Dive Planner (RDP), as it is widely
accepted and since the Professional Association of Diving Instructors (PADI) provided
initial project funding (5). Most of the dive profiles were at or near the limits of the RDP.
We did not test the DSAT tables exactly as prescribed. These tables specify an ascent rate
of 60 feet per minute, but we used an ascent rate of 30 feet per minute. In addition, for
dives at the no-stop limits, the DSAT tables specify a three-minute safety stop. We did
not use safety stops as they had not been used in previous flying after diving studies."
- page 33

"There were 802 exposures with 40 DCS incidents (5% DCS incidence). Twenty-one
cases were Moderate, 18 were Mild, and one was Serious. The serious case was cerebral
and occurred after a flight preceded by a three-hour surface interval. It resolved with
hyperbaric oxygen."
- page 33

Single dive exposures (p34):
\image{clipboard01.jpg}

repetitive dive exposures (p35):
\image{clipboard02.jpg}

"In conclusion,
(a) The diving exposures were at or near the RDP no-stop limits.
(b) The DCS incidence increased significantly as the PFSI decreased.
(c) Repetitive dives required significantly longer PFSIs to achieve low DCS.
(d) No DCS occurred in a total of 52 trials of a 17-hour PFSI."
- page 35

The full report is quite fascinating, especially the discussion at the end that led to the consensus recommendations.

The report, of course, has lots of caveats: cold immersion, exercise, decompression, etc. So putting an additional safety factor on is a good idea.


(Message edited by tursiops on January 15, 2009)

Hmmm, I'll try again on the two images:

Mel, thanks for the reference. Very useful. I would point, however, that the findings do support a bell curve as I mentioned.

I would like to bring your attention to the first of the two figures you posted. The curve for 60 fsw at 55 minutes resembles a normal distribution (aka, bell curve).

We can talk, at length, about how this bell curve translates into a profile for the diving population but let me re-assure you that the 18-hr interval is based on a normal distribution model.

I would not be suprised if you told me that the accurate model has its peak closer to the 12-hr surface interval. And that the 18-hr interval was selected instead to increase safety (and decrease legal liability for the recommending agency).

Leo, I'm not going to argue statistics with you on BT.

Mel - appreciate the info, your knowledge and effort to educate us. You are ahead of me. I will check for the details with DAN.

Thanks.

Dan

This is an excellent discussion and reference information thread.

But recall that that OP, who hasn't been back, asked simply about a low-altitude puddle-hop flight over to Curacao, not a 4-hour big jet flight with cabin pressure equivalent to 8000 feet elevation. There's a difference...

Tom, I would personally go diving the day before flying in a low-altitude aircraft. I'd limit myself to about 60 ft max and maintain a 12-hr buffer between the last dive and take-off.

But I would not advise anyone else to do so for two reasons. First, I have some empirical understanding of my physiology and my limits but not to that of others. Second, I would not want to be responsible for jeopardizing someone else's well being.

Statistics aside, I recognize the 18-h period as a golden rule for safety, based on common sense. And as much as I crave for one more dive on our last day in Bonaire, I can always hold my appetite for the next trip because I know there will be one.

Christy, it also depends on how many dives you have done the prior week and of course your age and if you are dehydrated as well.. if you are doing 4-5 dives a day max 60ft for 5 days it might not be a good idea.. I like the idea of taking the day and sightseeing the places you have been just too busy to see.. Or perhaps buying that piece of dive jewelry that you saw fleetingly in the window down town.. take all the above information and sort it out and I think you will see that most think it is not advised even for a short low flight.. WHY CHANCE IT???

freddie, you're right. why take the chance? there is plenty of stuff to do and see on land. after my hit of dcs we only do one, rarely two, dives a day. granted we are there for an extended period but i was serious when i said that spending four to six hours at at time in the chamber (you can't sleep or read and you can only talk or drink for about five out of every thirty minutes) is as bad as the symptoms. as my neighbor told me when he drove me to the hospital, "you're going to be able to breathe, drink water, and pee in the chamber...nothing else".

we always used our last day to shop or go to the park. anyone who has been on bonaire a week or two and hasn't toured the whole island is really missing something and the last day is a great day to sightsee.

There seems to be a lot of misinformation concerning "low-altitdue" aircraft.

First, it is important to understand how pressurized aircraft operate. When flying in a "large" commercial airliner, at 30,000ft +, your body is not experiencing that large of a pressure gradient. The cabin of a commercial airliner flying at high altitude will be pressurized to approximately 5,000 - 6,000ft. In other words, the body would experience the same pressure inside a commercial airliner at altitude as it would inside a non-pressuized "low-altitude" aircraft (a cessna for example) at 5,000 ft.

Now, "small" commercial airliners that fly between islands are most likely pressurized aircraft as well. A typical flight between islands might reach an altitude of 10,000 ft. Assuming the cabin is pressurized, you might experience a cabin pressure of around 4,000 ft. It is not a linear function between aircraft altitude and cabin pressure.

The lesson to be learned here is that "low-altitude" aircraft ARE NOT IN ANY WAY inherently safer as it relates to DCS risk.

The only exception to this would be a plane that flew at an extremely low altitude, say only a two thousand feet. This is dangerous and commercial airplanes do not do this, especially over water.

The difference in pressure between "high altitude aircraft" and "low altitude" island-hopping flights is VERY SMALL because of cabin pressurization systems. Anyone who assumes there is less risk because they are flying on a smaller plane is taking serious risks and fundamentally does not understand the nature of pressurized cabins.

The moral of the story is that the same rules should apply regarding diving after flying, regardless of the type of plane.

Pat,

I am curious about your comment that you cannot read or talk much in the chamber. I recall talking to people who said they read and I believe even play cards to pass the time. Is it something about the Bonaire Chamber that limits these activities? Is it only the patient that cannot do activities?

Sparty there is nothing allowed in the chamber that may create a spark in the O2 that is piped into it,,, so the patients are clothed in cotton and unless it is a see through chamber like some of the ones state side,, you cannot see the outside except through a small port hole.. One has to stay awake so that the doctor or tech knows that you are ok and not displaying other symptoms.. hopefully you are in an airconditioned chamber as there are some that are not air cooled.. like the one on Palau 10 years ago...

freddie's right...they limit combustibles in the chamber. yes, cotton will burn (pretty well actually) but it won't melt like synthetics. paper would contribute to the fuel load in case of a fire. the chamber isn't that big (i'd estimate maybe 7 or 8 feet long and about 4 feet in diameter) and could quickly become smoke-filled in a fire. the chamber attendants (there is always at least one person in there with you) are allowed to read. let's face it, they are volunteers and deserve an amenity or two.