18hr Flight Ban Valid After 5' Dive?

[Thalassamania]

It is a very bad idea to fly after full saturation at any depth which is why we have DO NOT FLY times following dives, to permit off gassing to reduce the residual nitrogen load to well below the saturation point.

Wrong. You normally fly at sea level saturation, you can saturate as deep as about 10 feet and still ascend to 8,000 feet. You can saturate as deep as about 20 feet and still ascend to the surface without staged decompression.

I believe we also need to define terms as I believe saturation is being misused here. Definition from Dictionary.com, "containing the maximum amount of solute capable of being dissolved under given conditions."

NOT THE EXPERT, but I do believe at 1 ATA our tissues and blood are well below the saturation point in terms of nitrogen loading. With each breath we inhale 78% nitrogen and at 1 ATA we lack sufficient pressure differential to cause it to cross over into our blood and be retained there. Ergo non-divers are not any where near reaching their saturation point. Now with an increase in elevation and the decrease in pressure it is true that some off gassing of nitrogen will occur (nitrogen is in our blood from chemical processes of the body. Note that 10,000 feet in elevation (airliners are pressurized to 7,000-8,000 feet elevation) results in only 31% reduction in pressure from 14.7 PSI to 10.2 PSI

You are kicking up silt, you need to stop and pay attention. Saturation means, as you posted, "containing the maximum amount of solute capable of being dissolved under given conditions." When you change the conditions, e.g., the ambient pressure, you change the amount of solute (nitrogen in this case) that is capable of being dissolved. If you saturate at a greater depth, you hold a proportionally greater amount of nitrogen. There is a depth at which the amount of nitrogen you are carrying will prevent you from safety ascending to 8,000 feet. As you saturate deeper and deeper your ceiling also descends. A bit beyond 20 feet you can no longer go to the surface without decompressing, At 40 odd feet (using air) you'll need (if memory serves) about 17 hours of decompression, at 160 you'll need about 50 hours (but that's heliox also). The advantage of saturation is that you don't take up more gas, no matter how long you stay, you only have to pay the decompression bill one.

 

[AbyssalPlains]

10 feet? You can board the airplane still dripping and you'll be fine.

 

[Bismark]

Wrong. You normally fly at sea level saturation, you can saturate as deep as about 10 feet and still ascend to 8,000 feet. You can saturate as deep as about 20 feet and still ascend to the surface without staged decompression.

You are kicking up silt, you need to stop and pay attention. Saturation means, as you posted, "containing the maximum amount of solute capable of being dissolved under given conditions." When you change the conditions, e.g., the ambient pressure, you change the amount of solute (nitrogen in this case) that is capable of being dissolved. If you saturate at a greater depth, you hold a proportionally greater amount of nitrogen. There is a depth at which the amount of nitrogen you are carrying will prevent you from safety ascending to 8,000 feet. As you saturate deeper and deeper your ceiling also descends. A bit beyond 20 feet you can no longer go to the surface without decompressing, At 40 odd feet (using air) you'll need (if memory serves) about 17 hours of decompression, at 160 you'll need about 50 hours (but that's heliox also). The advantage of saturation is that you don't take up more gas, no matter how long you stay, you only have to pay the decompression bill one.

The paragraph above summarizes things nicely. Thanks Thal. Now will everybody go back to diving and free up some bandwidth.

 

[mkutyna]

Perfectly obvious now that I read it but something that I hadn't realized before this. Thanks for the info.

A commercial airliner pressurizes the cabin over a schedule maintained by a pressurization controller. There is a minimum and maximum pressure differential. The maximum pressure differential, the ability for the pressure vessel to maintain integrity, dictates the service ceiling for the aircraft. The regulating athorities dictate a maximum cabin pressure of 8000 feet. The aircraft needs to be able to maintain a cabin altitude no greater than 8000 feet while flying at it's maximum certificated altitude. In the Boeing 737NG, that maximum altitude is 41000. There is conservatism built into this. While the aircraft climbs at say 2000 fpm, the pressurization controller climbs the cabin at around 300 fpm. If a 737 levels off at about 22,000 feet, the controller will maintain a cabin pressure of about 2000 feet since there is no need to max out the differential. As the plane starts climbing again to higher flight levels the controller will level the cabin at 8000 maximum.

 

[DandyDon]

Re OP, personally I have always thought the rules on flying after diving are way too conservative. If you fly a commercial airline the cabin is pressurised to 2,000 feet. I live above that altitude and have never felt a twinge from driving home after deep repetitive diving.

The answer I always get is: "Yes, but what happens if the plan suffers a rapid depressurisation?" The truthful answer is that you would be screwed, but I have yet to experience a rapid depressurisation on a commercial airline, and I suspect that is true of 99.99% of the world. Added to which, if there was a rapid depressurisation, you'd probably have better things to worry about at that instant (but, one the plus side, at least you'd be on O₂).

Sure, don't jump on a plane right after diving. But I think after 6 hours or so even after a regular dive you are sufficiently off-gassed to be at minimal risk, even in the (massively unlikely) event of a depressurisation.

Obviously different considerations apply for non-pressurised planes.

You weren't up to reading all of the thread huh?

• Risk of rapid depressurizing of a plane was covered.
• Some island jumpers fly below 2,000 in unpressurized cabins - under 1,000 on request, but jetliners are assumed to pressurize at up to 8,000. Flying at 8,000 ft equivalent after Open Water diving is what the 12 & 18 hour rules are based on.
• Our NOAA dive manual covers rules of traveling to 2,000 ft after diving; there are some standards you may not know, altho they are different from the 8,000 ft standards.
• And in the case of this months plane depressurizing, Oxygen was actually not available to all.

But back to your suggested 6 hour rule: Nope! It seems to be based on faulty science as you present your logic, and quiet dangerous. But if you thot that jetliner were commonly pressurized to 2,000 ft, that would suggest the source of your potentially dangerous mistaken thinking.

Non-Divers are not near nitrogen saturation and therefore at no risk when flying.
Flying for a diver who has reached nitrogen saturation point is dangerous, hence the no fly limitations.

Saturation by the way is defines as: the point at which a solution is incapable of absorbing any more of a chemical into that same solution.

At 1 ATA nitrogen is not being forced from the ambient air into our blood stream in any significant amount. Nitrogen does come into our blood as a result of chemical processes of the body and waste products.

Airliners fly pressurized to between 7,000 and 8,000 feet elevation. At 1 ATA (sea level) we are at 14.7 PSI, at 10,000 we are at 10.2 PSI or a 31% reduction in pressure.

Conversely at 5 FSW (an the question was about pool water which is lighter) we are at approximately 1.15 ATA or roughly 16.91 PSI.

Pssst. A non-diving person's body saturates at 14.7 psi at sea level; it's just not a dangerous saturation. Really, the thread has had some interesting points, you might enjoy reading all of it, but nonetheless - that's really a good idea when posting in a long thread.

Wrong. You normally fly at sea level saturation, you can saturate as deep as about 10 feet and still ascend to 8,000 feet. You can saturate as deep as about 20 feet and still ascend to the surface without staged decompression.

You are kicking up silt, you need to stop and pay attention. Saturation means, as you posted, "containing the maximum amount of solute capable of being dissolved under given conditions." When you change the conditions, e.g., the ambient pressure, you change the amount of solute (nitrogen in this case) that is capable of being dissolved. If you saturate at a greater depth, you hold a proportionally greater amount of nitrogen. There is a depth at which the amount of nitrogen you are carrying will prevent you from safety ascending to 8,000 feet. As you saturate deeper and deeper your ceiling also descends. A bit beyond 20 feet you can no longer go to the surface without decompressing, At 40 odd feet (using air) you'll need (if memory serves) about 17 hours of decompression, at 160 you'll need about 50 hours (but that's heliox also). The advantage of saturation is that you don't take up more gas, no matter how long you stay, you only have to pay the decompression bill one.

There ya go....

 

[Thalassamania]

Saturation is traditionally thought of as 24 hours, that's what you need to become an Aquanaut, just like you need to go above 50 miles to qualify for Astronaut wings.

 

[DandyDon]

Post 64 also shows disagreement/confusion from other people regarding Mempilot's response to the original question of flying after a pool dive.

I only have 4 pages; got my settings for 40 posts per page - saves turning pages. Best to specify posts, but - those numbers can change. You can link to a particular post or quote it.

 

[nwhitney2003]

I only have 4 pages; got my settings for 40 posts per page - saves turning pages. Best to specify posts, but - those numbers can change. You can link to a particular post or quote it.

Didn't realize that. Thanks, I'll do that instead.

 

[Thalassamania]

With respect to flying: The UHMS, DAN, AAUS, etc., recommendations are all highly conservative and were all made looking over our shoulders at the lawyers. Here's reality:

1. Nothing is "safe."
2. Always remember that your spinal column has been very, very good to you, without it locomotion, bladder, bowel and sexual function is compromised.
3. "Acceptable risk" (for me) is the old U.S. Navy guidelines, which permitted you to be a a bit more than Group-C ("new" Group-D diver), but not an "old" (almost Group-E) diver. I cut that back to Group-C, period.
4. Two hours of surface breathing pure oxygen will take you from Group-N to Group-A.
5. Do your own research, draw your own conclusions, decide on the level or risk that you can accept.

 

[LavaSurfer]

Only one this month.

That was awesome!
Timing IS everything is it not?