18hr Flight Ban Valid After 5' Dive?

[ReefHound]

I'm not seeking the answer to the original question. Calling DAN is ONE logical source for the correct answer. Look back at a couple of post and you'll see that I also mention other options.

Post 105 is a good place to start as any I suppose. I think this is a good example over the disagreement. Thalassamania's post clearly shows a disagreement with Mempilot in regards to the answer of the original question.

You seem to be confused about what was the original question. It was (actually there were two but this is the one everyone is discussing): "However, is it possible for this rule to be reduced or are there other guidelines for people who are only diving very shallow? As I mentioned, the pool is only 10 ft deep, so obviously it is a very shallow dive."

There is nothing in post 105 or any other post where anyone answered that the standard no-fly time is not possible to be reduced after a pool dive or that it is unsafe to fly after a pool dive.

Both Thal and Mem have stated that flying after a pool dive is Ok. There is no disagreement there. Thal and Mem are disagreeing over full saturation levels and depths, which was not part of the original question.

 

[mempilot]

Thal and Mem are disagreeing over full saturation levels and depths, which was not part of the original question.

We really aren't disagreeing on anything, because I agree with him on this too.

He just feels the need to take a typo (absense of the word 'not' which I admit I missed while I was typing half asleep last night), and take it out of context to prove himself superior to me. He can have that title. If wants to make everyone think I'm unsafe and don't have the knowledge of one of his basic students, more power to him. I don't really care. The fact that I fixed a typo is not backpeddling, as my meaning is still the same. Some of these guys just smell blood. Oh well.

The disagreement from me about his post had to do with the nature of his comment which would lead a new diver down the path of misconception about deeper dives and flying. So, while he stills seems to want to argue, about what I have no idea, this thread was pretty much over 50 posts ago.

 

[mempilot]

You are absolutely right, and I apologize for missing it. T&S brought it to my attention and I fixed it, only to be jumped on again for doing so. Damned if I do, damned if I don't.

Guys,

I'm sorry for the confusion. Please find another topic.

Hoo boy, the word 'not' is a modifier that changes the meaning 180 degrees. I didn't see the 'typo' corrected (I don't re-read the entire thread every time I log on) but saying this earlier could have prevented a lot of confusion instead of attacking everyone who took your words at face value instead of reading your mind as to what you meant to say.

 

[Rhone Man]

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.

 

[pasley]

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.

 

[mempilot]

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.

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.

 

[mempilot]

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

Not quite correct about the 10000 aircraft altitude to maximum 7-8000 cabin altitude, but you are on the right track.

At 10000 feet aircraft altitude, the cabin would be maintained closer to sea level. As the aircraft climbs, the controller would not be able to maintain a low cabin pressure, and therefore it starts climbing the cabin slowly.

 

[nwhitney2003]

Because you want to know the correct answer to the original question? And according to you, that's the most logical source of the correct answer?



Um, OK. Care to provide post numbers or quotes where anybody said that flying after a short pool dive was unsafe? All the disagreement has been over the side issues that arose afterward.

You seem to be confused about what was the original question. It was (actually there were two but this is the one everyone is discussing): "However, is it possible for this rule to be reduced or are there other guidelines for people who are only diving very shallow? As I mentioned, the pool is only 10 ft deep, so obviously it is a very shallow dive."

There is nothing in post 105 or any other post where anyone answered that the standard no-fly time is not possible to be reduced after a pool dive or that it is unsafe to fly after a pool dive.

Both Thal and Mem have stated that flying after a pool dive is Ok. There is no disagreement there. Thal and Mem are disagreeing over full saturation levels and depths, which was not part of the original question.

I'm not confused. The original question was in regards to flying after diving in a pool. The disagreement came from a typo from Mempilot (left out the word "not") and many folks jumped all over him for that. He realized his mistake and fixed it. Post 105 does show this disagreement.

 

[24940]

Saturation point is a variable. The degree of saturation is driven by ambient pressure. We are saturated at any depth at the point we no longer on gas at that depth. Saturating at 5' depth and popping up to 8000' is no more dangerous than doing the same after being saturated at sea level.

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.

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

 

[mempilot]

For those who care, here is a picture of a DCPCS on a B737-800. The lower right part of the panel has a placard that shows an expected maximum cabin altitude target. It is used when we have to manually control the outflows valves after a dual digital controller failure. It allows us to manipulate the cabin altitude based on what the controller would have been aiming for prior to going tango uniform. You can look at the bottom row of numbers and multiply them by 1000 to get flight altitude. The top row corresponds to the target cabin pressure at that lower rows altitude. Note that the chart stops at 8000 feet for cabin pressure and 37000 for flight altitude. The older B737's were capped at FL370, but the newer 737's were certified to FL410. The pressurization system stayed basically the same between the -300, -400, -500, -600, -700, -800, and -900. The NG series, -600 through -900 were certified with a higher differential than the older models.