to wait or not to wait

[fins wake]

Re-reading the posts and thinking about it again, you've used exactly the right terminology, everything you write makes perfect sense and I've been barking up the wrong tree.

My sincere apologies for obfuscating the issue at the end. :bonk: :dork: :blush:

If it helps, I will gladly reiterate that

Charlie's example shows why flying after diving has to be taken seriously.

:drain:

 

[MonkSeal]

fins wake once bubbled...
He will probably be given the advice to lower the cabin pressure as much as he can (which often involves actually flying lower as well to make this easier) and then to land at an airport near a hyperbaric chamber.

Lower altitude means higher pressure

 

[fins wake]

Lower altitude means higher pressure

This is all connected to my reply to Charlie, but I think I've apologized enough now, right? I'll blame the hot weather here, sunstroke or heat stroke or something ...

I do know this, honest!

 

[Charlie99]

fins wake once bubbled...
I do know this, honest!

I assume that you do. Measuring pressure in feet of altitude causes the same sort of confusion as when my wife asks me to "turn up the air conditioning". Her "turn up" means to increase the level of air conditioning by setting the thermostat lower. My "turn up" is just the opposite.

Written communication is sometimes a balancing act between being too verbose and therefore your message being buried; and too terse and your message being unclear. If I had used the phrase "pilot reduced cabin pressure to ...." rather than "had to depressurize to.... " the issue wouldn't have come up.

In any case, your command of English is much better than my Swedish


Charlie

 

[pasley]

I agree with everyone. Wait to fly and skip the morning dives.

Let’s look at the risk factors here for a second.
1. You do not say why you are not diving before the night dive so I will take a stab and bet you are flying in that day. The airlines push liquids (the wrong ones with sugar and caffeine) because the cabin air is very dry. This explains why on long flights your sinus gets all crusty. Dehydration increases your risk of DCI. So if you are flying in this day, diving that night is a higher risk for DCI than normal. Push the water on the plane and think of waiting. DAN has had articles on this and recommends a quiet evening at the hotel resting and hydrating on the day you arrive at your dive destination.

2. The morning dives with a proper surface interval (as long as possible) between them to reduce your residual nitrogen load will, depending on the depth and duration of the dives, potentially make it tough to get in the 2 dives and still have a decent surface interval before flying.

3. Diving and DCI are full of unknowns. You can do everything right, and by the book and still get DCI. Two divers of the same age and general fitness levels on the same dive, one may get DCI and one may not. So much is unknown and the variables from person to person, such as blood pressure/volume, hydration, heart health, past injuries, etc. The best recommendation the industry currently has, based on the general population is to wait 24 hours. That has increased from a few years ago. You may get away with it or you may not.

4. Are you really ready to gamble your life or possible permanent injury on getting in a couple of dives in a higher risk situation? What you are considering is an activity that puts you at a higher risk for DCI. Two years ago I did a by the book dive where all the rules were followed but I still got bent in what they term “undeserved Decompression Illness”. I continue to have a tingling sensation in my foot two years later and am happy that is all I have. I could be paralyzed or dead.


So skip the dives or extend the stay a day or two. Relax and live to dive another day.

 

[pescador775]

Finswake, in the event of a door ajar, it would make sense to lower cabin pressure AND decrease altitude. Raising the outside pressure while decreasing the cabin pressure would presumably be the preferred method for forcing the door closed. I see nothing wrong with your account of things.

 

[BigJetDriver]

If I may, just a little bit of Airplane Door 101.

Aircraft fuselage doors are "plug" type doors. They swing inward momentarily, then pivot, and slide out through the opening. In the closed position, pressure inside the hull forces them into the frame of the door tighter because of their beveled edges. When you add up the total surface area of the door, times the pressure per square inch in the cabin, you realize that even "Arnold" couldn't open that door if the hull is pressurized!

Cargo doors, on the other hand, open outward. They are held closed by many, very strong, over-center latch mechanisms, when everything is working properly. Should one come open, due to some mechanical failure, the only answer is to depressurize the aircraft, which will reduce the pressure forcing the door outward. Descending, slowing, and finding a place to land are usually part of the game plan. If the door rips off the fuselage, especially if it is a door forward of the engine intakes, it will tend to spoil everyone's day!

The problem for a diver who is onboard, who has a load of nitrogen onboard HIM (or her), is that the equation has suddenly and drastically changed. Instead of being at around 6500 to 7500 feet in cabin altitude, he is now at whatever altitude the cabin gets to in this process. IT COULD BE VERY HIGH, INDEED, at least until the pilots get the aircraft down to a lower altitude. He or she could be in serious bubble-trouble!

Modern transport aircraft are extremely reliable, but CAN this happen? We have at least one story of exactly that happening in previous messages in this thread. It IS worth taking the possibility into account when planning your vacation dive strategy! After all, what is your body worth to you, in good working condition?

 

[Charlie99]

BigJetDriver69 once bubbled...
If I may, just a little bit of Airplane Door 101.

The problem for a diver who is onboard, who has a load of nitrogen onboard HIM (or her), is that the equation has suddenly and drastically changed. Instead of being at around 6500 to 7500 feet in cabin altitude, he is now at whatever altitude the cabin gets to in this process. IT COULD BE VERY HIGH, INDEED, at least until the pilots get the aircraft down to a lower altitude. He or she could be in serious bubble-trouble!

My guess is that the alarm showed up as soon as there was a significant pressure differential forcing the door out, because we were no more than about 15,000 ft altitude and less than 10 minutes after takeoff from Kahalui (Maui) airport before we hung a left turn and headed for Honolulu instead of SFO.

I was paying close attention because I was feeling lightheaded and my fingernail beds were slightly blue. My fellow passengers were surprised when I commented that it looked like we were diverting to Honolulu, and it took another 10 minutes before the pilot made any announcement. Having done a dive the previous night, I was probably one of the few passengers that was happy to hear that it was a mechanical malfunction (as opposed to some weird DCS symptom).

The pilot obviously decided that the best PR was to keep the passengers informed, so as we circled around burning off fuel, the pilot explained in some detail about current cabin pressure, cabin pressure at which O2 masks drop, and details on the various levels of overweight landing vs. the level of post landing inspection required. Since we started with lot of fuel, even after burning off some we still landed significantly above normal landing weight limits and it took about 40 minutes of inspection to clear the plane for further flight. The cargo door problem was just a bad sensor and it about the same time to fix.

BigJetDriver69 once bubbled...
If I may, just a little bit of Airplane Door 101.
Aircraft fuselage doors are "plug" type doors. They swing inward momentarily, then pivot, and slide out through the opening. In the closed position, pressure inside the hull forces them into the frame of the door tighter because of their beveled edges. When you add up the total surface area of the door, times the pressure per square inch in the cabin, you realize that even "Arnold" couldn't open that door if the hull is pressurized!

A niece who is flight attendant discovered this upon landing in Denver. The automatic system for equalizing pressure was out of service and they pulled up to the gate with the cabin pressure at a lower altitude (higher pressure) than the 5,000' of Denver. They managed to crack open the door open a bit by using a lot of force, but quickly figured out something was quite wrong.