18hr Flight Ban Valid After 5' Dive?

[mempilot]

I believed that a 1/2 life was 50%, 75% 87.5% etc.

Yes.

Take your 20 min compartment.
It starts at 0.79bar because that's what you're breathing on the surface.

I was actually looking at a 40 minute slow compartment, not a 20.

I use .78 since I'm only looking at N2 and not the other trace gasses in my example. 21% O2; 78% N2; 1% other trace gasses

The target is 4m depth so 1.4 bar absolute so 1.4*0.79=1.106 bar N2 (assuming you're breathing air).

My target in my example was 10 fsw (3.3 m), so 1.3 * .78 = 1.014 bar N2 fully saturated

After the first 20 mins it gets half way (0.79+1.106)/2 = 0.948bar

After first 40 minutes: (0.78 + 1.014) /2 = .897

After the next 40 min: (.897 + 1.014) /2 = .956

And so on down to the sixth rotation through the equation until full saturation.

I'm pretty sure we were on the same page. I just didn't actually run the equations through to figure the BAR, but it's still a long time like you said.

 

[mempilot]

I think the disagreement is about Mempilot's seeming contention that saturation at 5 ft. has similar or the same potential implications as saturation at other depths.

Ummm. That's not what I said. I said that saturation is saturation, no matter what the depth. Meaning, saturation at 5 fsw has the same definition as saturation at 100 fsw. The tissue has ongassed to it's equilibrium and won't accept any more gas without increasing pressure. This may be where I wasn't clear, and the cause for confusion about my point.

 

[mkutyna]

I concede that I did give out incorrect advice regarding taking a nap after diving. That bit slipped my memory and I apologize. I still think that it was a good idea to disavow the OP's notion of exercising after diving (notice I said "diving", not "diving in a pool" in both this and my original post).

Lastly, I completely agree with TS&M and Thal that it is okay to be saturated at 5fsw and then hop on a commercial airplane that has the cabin pressurized to 8000'. Honestly, how often do cabin depressurization events happen in commercial passenger jets that don't result in the plane crashing? I can only think of two, ever.

 

[mempilot]

All very sound advice.

I'm sorry if I came across crass. I was very tired and grumpy last night, and I was posting at 2 am. Bad combination! Sometimes the brain and the fingers aren't on the same page.

I concede that I did give out incorrect advice regarding taking a nap after diving. That bit slipped my memory and I apologize. I still think that it was a good idea to disavow the OP's notion of exercising after diving (notice I said "diving", not "diving in a pool" in both this and my original post).

Lastly, I completely agree with TS&M and Thal that it is okay to be saturated at 5fsw and then hop on a commercial airplane that has the cabin pressurized to 8000'. Honestly, how often do cabin depressurization events happen in commercial passenger jets that don't result in the plane crashing? I can only think of two, ever.

 

[shadragon]

BTW, the poster commenting on aircraft pressuration: please don't. You're just passing on more bad information.

As a former Air Force Technician with certifications on multiple transport, patrol and fighter airframes I have considerable experience in pressurization and how much it varies. No airframe is 100% air tight, all the time. Air is pumped in and vented continuously. Air leaks cause internal air pressure to vary. It drops over time then the systems repressurize it back up. It drops then the systems repressurize it back up. Again and again. This can sometimes be equivalent to thousands of feet change in altitude.

"As the airplane pressurizes and decompresses, some passengers will experience discomfort as trapped gasses within their bodies expand or contract in response to the changing cabin pressure. The most common problems occur with gas trapped in the gastrointestinal tract, the middle ear and the paranasal sinuses. Note that in a pressurized aircraft these effects are not due directly to climb and descent, but to changes in the pressure maintained inside the aircraft." Reference Link This is when the system is working correctly...

Saying 'it isn't so' does not make it so.

Oh and the quote in your sig line, "Would you mind not shooting at the thermal nuclear weapons?" should be "Would you mind not shooting at the thermonuclear weapons?" John Travolta in Broken Arrow. Unless you are referring to an ICBM warhead with scarf and mittens.

 

[DandyDon]

Honestly, how often do cabin depressurization events happen in commercial passenger jets that don't result in the plane crashing? I can only think of two, ever.

Only one this month.

 

[nwhitney2003]

Most instructors have been taught a basic level of knowledge of gas loading. Instructors who teach technical level courses, as well as some recreational instructors, have a higher understanding of tissue loading and offgassing.

Many of the rules; ie. 12, 18, 24 hours dive to fly time are guidelines set at very high limits. NOAA advocates another set of rules that actually look at ending pressure groups and actual cabin pressure altitudes for ascent to altitude after diving. The point I tried to make earlier, is that people know the rules they were taught, but they don't neccessarily understand the real data behind it.

You will get all kinds of "The sky is falling." type of guidance from the vast majority of divers. I'll tell you that your instructor and their agency should be your first avenue for furthering your knowledge of something you don't understand. Trying to learn it on the web can be garbage in, garbage out.

If you don't learn what you need to know from your instructor, might I suggest moving on to another level of diving where the specifics are taught to every student.

DAN is a tool, and I'd encourage you to call them when needed. But don't use them as a replacement for good training. A good instructor who teaches for an agency that puts this knowledge in their hands is the proper starting point.



You are absolutely right with these two statements. Read as much literature as you can on a subject. SB is not literature. Then call them if you need clarification.

But the question being asked, while obviously not easy to the original poster, should have had a very simple answer:

Yes, you can fly after a pool dive as long as you didn't live at 10 feet.

Calling DAN to get that answer would have been a waste of good resource and was actually something SB could have answered without the complications of people throwing all kinds of whacked out references to confuse the poster.

I'm sorry if you felt I jumped on you personally. I didn't mean to attack you. I keep that DAN number handy, as I've had to use it in the past to ask about baratrauma to an ear while on vacation once. They were invaluable to me, as they are to others.

I don't feel as if I've been jumped on personally and I don't feel attacked so no worries there. My point is that (and you agreed with me) the post on here can be hard for a new diver to sort through. So why should a new diver take your advice, as accurate as it may be, over someone else? My point in calling DAN was not to necessarily get a quick answer but to become educated and I wasn't very clear about that. I think we would both agree that divers need to continue their education. Certifying agencies are not the only way to increase diver knowledge, hence my suggestion about DAN. The OP has gotten so many different answers to this question so where do they begin to sort out the bogus information?

 

[Blackwood]

My comments about flying after diving in a pool were about someones comments about saturation, and my point was that it takes many hours to saturate at 5 fsw.

There seems to be a serious lack of careful reading going on. A few of you are very quick to open your mouths before you open your eyes. Please read every word and sentence. Comprehend first, then type.

Like TSM, I too try to read fairly carefully. It seemed to me that your point wasn't that it takes a long time to saturate, but that flying after saturation at any depth is a bad idea.

I guess that misinterpretation comes from my inability to comprehend posts such as: "To fully saturate at any depth and then ascend to altitude without decompressing would end badly."


Taken in conjunction with posts like "Saturation is saturation, no matter what depth you stayed at to get saturated," it is not unreasonable to conclude that you are suggesting saturation at 5FSW is the equivalent to saturation at any other depth. While the implications for further ongasing at that depth are the same, the pressures most certainly are not, and it is the pressures about which we as divers are concerned.

Thal (to my best comprehension) brought up saturation (the extreme end of ongasing) in such a way to completely dismiss the worries of flying after dives to such benign depths. Somehow that statement got you bent way out of shape even though it's completely valid.

The long and short of it is: if it were a bad idea to fly after full saturation at any depth, no one would ever fly since even non-divers have saturated at some depth (zero FSW, on average), and certainly no divers could ever fly since they load their tissues to much beyond 5FSW saturation on a regular basis.

 

[ReefHound]

I don't feel as if I've been jumped on personally and I don't feel attacked so no worries there. My point is that (and you agreed with me) the post on here can be hard for a new diver to sort through. So why should a new diver take your advice, as accurate as it may be, over someone else? My point in calling DAN was not to necessarily get a quick answer but to become educated and I wasn't very clear about that. I think we would both agree that divers need to continue their education. Certifying agencies are not the only way to increase diver knowledge, hence my suggestion about DAN. The OP has gotten so many different answers to this question so where do they begin to sort out the bogus information?

So just call DAN and be done with it. Then tell us what they say. You've spent more time and energy justifying calling DAN that it would take to actually do it.

I don't really see where the OP has gotten different answers to the question he actually posted - is it safe to fly after a short pool dive. Did I miss where someone said it was not? Where the differences come in concern the theoretical issues of full saturation amid a bunch of bickering and insulting.

 

[mempilot]

First of all, your original comment lay with the flight crew, so your defense based on the airframe below is apples to oranges over your initial comment that I responded to.

You don't need to quote me on aircraft pressurization. I have been flying pressurized aircraft for over 20 years.

Air leaks cause internal air pressure to vary. It drops over time then the systems repressurize it back up. It drops then the systems repressurize it back up. Again and again. This can sometimes be equivalent to thousands of feet change in altitude.

This is a gross exageration of reality. You are correct in the fact that the pressure vessel is not 100% sealed. The packs boost pressure to overcome the natural leaks. The outflow valves modulate to maintain a constant pressure differential.

Any aircraft you speak of that fluctuates thousands of feet should be grounded. A rapid rise in cabin altitude much less than that would set off a master caution and indicate a problem with the controller or cabin pressure.

Saying 'it isn't so' does not make it so.

Who said it wasn't????

Oh and the quote in your sig line, "Would you mind not shooting at the thermal nuclear weapons?" should be "Would you mind not shooting at the thermonuclear weapons?" John Travolta in Broken Arrow. Unless you are referring to an ICBM warhead with scarf and mittens.

It's a joke, get over it.