Can I calculate the time before flight by myself?

[PfcAJ]

I've heard from a well decompression researcher that getting bent while flying is one of the worst things. The pain, delay in treatment, and the after effects.

 

[Adobo]

I am not really clear on your point here.

The flying after diving rule is based on the effects of a rapid ascent with at least a 2,000 foot elevation gain from your present altitude. If you are flying in a pressurized plane after leaving Lake Tahoe, then you are within the 2,000 feet of that altitude and should not have to wait at all.

Ascending from depth to the surface at altitude (or at sea level) is a totally different situation altogether. There you are making calculated stops along the way. How altitude affects those stops is a matter of great debate. UTD says it has so little effect it does not have to be considered in decompression planning. Most decompression algorithms, however, do think it makes a difference and plan accordingly.

You have a similar problem driving to altitude after a dive. The NOAA tables are helpful with that, because they have more increments.

What are these calculated stops? In recreational diving, it is 1ATA/minute till you get to 15ft where you do an optional 3-5 minute safety stop. From there, you have a 30 second ascent to the surface.

If you are diving at Lake Tahoe, at the end of your dive, you are now at 6200ft altitude.

Is that more benign than someone who dives the same profile in the ocean and 6 hours later gets on a commercial flight and at some point during the flight experiences reduced pressure equivalent to 8000ft altitude?

 

[boulderjohn]

There are divers doing tech dives in Lake Tahoe (altitude at lake surface = 6200ft.).

What are these calculated stops? In recreational diving, it is 1ATA/minute till you get to 15ft where you do an optional 3-5 minute safety stop. From there, you have a 30 second ascent to the surface.

If you are diving at Lake Tahoe, at the end of your dive, you are now at 6200ft altitude.

Is that more benign than someone who dives the same profile in the ocean and 6 hours later gets on a commercial flight and at some point during the flight experiences reduced pressure equivalent to 8000ft altitude?

Your original post said tech dives, so I assumed you were talking about staged decompression stops.

Your post seems to imply that divers are under the same pressure under water at altitude as they are at sea level, and then, boom, they emerge to altitude. In fact, they are under different amounts of pressure at each depth as they ascend. That is why recreational divers are taught to use theoretical depth at altitude rather than actual depth at altitude to plan their dives. They are therefore taught to dive different times and depths at places like Lake Tahoe, and, yes, the primary reason for this is the decreased pressure when they emerge from the water.

To give a very quick summary, the problem at altitude is not the difference in pressure at any one depth; it is the change in pressure upon ascent that is different from the change in pressure at sea level upon ascent that makes the difference. The pressure at 100 feet of depth is very similar to to the pressure at that depth at sea level, so the rate of N2 ongassing is similar. The diver beginning an ascent at altitude will have about the same tissue loading as a diver at sea level. The pressure at 15 feet, though, is very different--it is much less. That means that there is a greater pressure gradient for the diver at that depth than at sea level, and if the diver were to ascend and surface as at sea level, there would be a potentially dangerous gradient increase.

As I said, the effects of altitude on diving are controversial. If you read Bruce Weinke on the subject, you will see something entirely different from what you would glean from a chat with Andrew Georgitsis. I have seen the argument you make from those of the AG school, and I have seen the opposite.

 

[Adobo]

Your original post said tech dives, so I assumed you were talking about staged decompression stops.

Your post seems to imply that divers are under the same pressure under water at altitude as they are at sea level, and then, boom, they emerge to altitude. In fact, they are under different amounts of pressure at each depth as they ascend. That is why recreational divers are taught to use theoretical depth at altitude rather than actual depth at altitude to plan their dives. They are therefore taught to dive different times and depths at places like Lake Tahoe, and, yes, the primary reason for this is the decreased pressure when they emerge from the water.

I imply no such thing.

I am interested though, what is the magic ascent technique used by Tahoe divers that they do not need to wait 24hrs before they go to 6200ft of elevation.

To give a very quick summary, the problem at altitude is not the difference in pressure at any one depth; it is the change in pressure upon ascent that is different from the change in pressure at sea level upon ascent that makes the difference. The pressure at 100 feet of depth is very similar to to the pressure at that depth at sea level, so the rate of N2 ongassing is similar. The diver beginning an ascent at altitude will have about the same tissue loading as a diver at sea level. The pressure at 15 feet, though, is very different--it is much less. That means that there is a greater pressure gradient for the diver at that depth than at sea level, and if the diver were to ascend and surface as at sea level, there would be a potentially dangerous gradient increase.

As I said, the effects of altitude on diving are controversial. If you read Bruce Weinke on the subject, you will see something entirely different from what you would glean from a chat with Andrew Georgitsis. I have seen the argument you make from those of the AG school, and I have seen the opposite.

Shrug.

Lake Tahoe is at 6200ft elevation. From what I have heard, commercial flights are pressurized to equivalent of 8000ft elevation.

Divers are diving recreational profiles at Tahoe. They are not doing 24hour deco stops at whatever depth would equal sea level before ascending to the surface.

Divers are diving technical profiles at Tahoe. They are incurring greater inert gas load than the recreational divers. They are not doing 24hour deco stops at whatever depth would equal sea level before ascending to the surface.

I'm not suggesting that a diver at Tahoe should use the same techniques at Tahoe as they would at sea level. Just saying that the 24hour rule sounds more like an old wives tale than something that is the result of real data/research/experience.

 

[RonFrank]

Here is one experts opinion. There is a reason I generally wait 24 hours after diving as I have read a LOT on this subject. As I live close to 9000' I have read a lot on altitude diving as well.

PADI makes their recommendations, but I do not base my diving decisions on just PADI. I dive a lot on vacation, but leave myself room when flying. Others can do what they are comfortable with.

"Flying after Diving
By Fred Bove, M.D., PH.D.
.....
Recommended intervals before flying range from 2 to 12 hours for no decompression diving. A reasonable recommendation is that divers who have had less than two hours total no decompression dive time during the 24 hours before flying should wait 12 hours before flying. Divers who do multi-day diving should wait 18 to 24 hours before flying. Bubbles present from a previous dive may not cause problems on the surface but may cause decompression sickness as they expand at altitude. To avoid bubbles, dives should be conservative. You can minimize risk by reducing total diving exposure on the last two days before traveling by aircraft. ......."

Link to full article
http://www.skin-diver.com/departments/diversafety/flyingafterdiving.asp

 

[boulderjohn]

I'm not suggesting that a diver at Tahoe should use the same techniques at Tahoe as they would at sea level. Just saying that the 24hour rule sounds more like an old wives tale than something that is the result of real data/research/experience.

OK, I am totally baffled by this part of your response. Let's start by looking at what I said that you took issue with:

It is my understanding that DAN's initial 24 hour rule was a seat-of-the-pants guess with nothing to back it up. They then did the extensive studies that led to the 18 hour rule that, as Don said, has been in effect for a decade. If you read the details of the study, you will probably get the sense (as I did) that even the 18 hour rule is pretty conservative.

So, I said the 24 hour rule was nothing more than a "seat-of-the pants guess," and you seem to be attacking my advocacy of a 24 hour rule. I'm lost.

Dan has published the studies they did and their results. As I said earlier, I think they indicate that the 18 hour rule may be conservative. (And it is actually only 18 hours for multiple dives--it is otherwise 12 hours.) You can read the study and tell them that they actually did not do the research they did and that they were relying on old wives tales for their work if you want.

My reading skills seem to be deteriorating in my old age--I really had trouble understanding what you were saying in the rest of the post. I apologize for that.

 

[Adobo]

OK, I am totally baffled by this part of your response. Let's start by looking at what I said that you took issue with:

So, I said the 24 hour rule was nothing more than a "seat-of-the pants guess," and you seem to be attacking my advocacy of a 24 hour rule. I'm lost.

Dan has published the studies they did and their results. As I said earlier, I think they indicate that the 18 hour rule may be conservative. (And it is actually only 18 hours for multiple dives--it is otherwise 12 hours.) You can read the study and tell them that they actually did not do the research they did and that they were relying on old wives tales for their work if you want.

My reading skills seem to be deteriorating in my old age--I really had trouble understanding what you were saying in the rest of the post. I apologize for that.

What we have here... is a failure.... to communicate.

I am not attacking anything you are saying. I am extending what you are saying. Not only do I think the 24 hour rule is bogus (which is sort of along the lines of what you said), the 24 hour rule seems to go against what Lake Tahoe divers are experiencing. Full stop.

 

[boulderjohn]

What we have here... is a failure.... to communicate.

More evidence of a decline in my reading skills in my dotage.

 

[RonFrank]

[SIZE=+1]Some research from DAN. BTW those claiming a 24 hour rule is bogus should really read up on the subject. 24 hour may not be enough in some circumstances.

"The Undersea and Hyperbaric Medical Society conducted a workshop on flying after diving in 1991 after their controversial recommendations were made in 1989 and this was supported by DAN and diver certification agencies in their publications. Some diving groups were pleased, others felt they were too conservative and unnecessarily constrictive to recreational divers.[/SIZE]

[SIZE=+1]The final upshot of the debate is a DAN revised guideline which states:[/SIZE] [SIZE=+1]a. A minimum surface interval of 12 hours is required before ascent in a commercial aircraft (8000 foot (2438 m.) cabin).[/SIZE] [SIZE=+1]b. Wait an extended surface interval beyond twelve hours after daily, multiple dives for several days or dives that require decompression stops[/SIZE] [SIZE=+1]c. The greater the diving the longer the duration recommended before flying.[/SIZE] [SIZE=+1] The above is for sports diving and should not apply to commercial diving or nitrox diving. Because of the complex nature of DCS and because decompression schedules are based on unverifiable assumptions, there can never be a fixed flying after diving rule that can guarantee prevention of bends completely.[/SIZE]

---

Full Article Flying After Diving-

 

[Adobo]

Here is one experts opinion. There is a reason I generally wait 24 hours after diving as I have read a LOT on this subject. As I live close to 9000' I have read a lot on altitude diving as well.

PADI makes their recommendations, but I do not base my diving decisions on just PADI. I dive a lot on vacation, but leave myself room when flying. Others can do what they are comfortable with.

The article also states:

Theoretical calculations for a dive to the no decompression limit followed by a flight indicate that six to eight hours is adequate for a commercial flight following a single dive. The typical sport diving pattern of multiple dives over several days followed by flying has not been analyzed theoretically.

No details on what assumptions were made for this theoretical dive. Like the dive profile (130 for 5 mins or 50 ft for 50 mins?). Or the the ascent profile. Or the safety/deco stop.

Further it states:

in a given year there are likely to be at least 300,000 to 400,000 people who fly home 12 to 24 hours after their last dive. The incidence of decompression sickness among these divers is estimated to be about 0.004 percent. This low incidence indicates current procedures are safe.

So it seems the 24 hour recommendation is safe. But the article doesn't indicate how 24 hrs is materially more safe than say 18 hours. Or even 12 hours.

Finally, it states:

Basic guidelines for vacations should include conservative diving, limiting repetitive dives to three per day, doing only no decompression dives that are not at the no decompression limits and reducing total diving time in the last day or two. Flying should be done the day after diving is finished. Even though this may not be a full 24 hours after diving, experience to date indicates this will produce...

Clearly, this article is not meant to be the end all and be all of recommendations when it comes to flying after diving. I know plenty of people who travel and do technical dives. I know plenty of people who travel and do more than 3 dives a day.

It would be great to hear about some of the data/science you might have picked up in some of your other reading as it relates to altitude diving and flying after diving.