Diving at altitude

[scubajoe]

I have a few concerns about advice given on diving at altitude. I was trained and now teach students that diving at altitudes over 1000 ft above sea level require additional training. I believe my training. Has anything changed regarding altitude diving? I understand there is no difference in the pressure exerted by the water regardless of the altitude. However it looks to me like there is the same effect when you surface as when you fly after diving.
Any opinions? Or better yet, facts!


Joe

 

[MikeFerrara]

As far as I know you're correct. The math is pretty simple.

Since you're at a lower pressure some depth gauges will be off by the difference in atmospheric pressure.

Also you're surfacing to a lower pressure so a given depth at altitude needs to be treated as a deeper depth (theoretical depth). That's because decompression tables are usually designed for sea level.

Most decompression software let you specify altitude and adjust and many computers compensate automatically also.

Now, I think there are some that suggest that since decompression isn't an exact science anyway and if you are following certain procedures that the relatively small difference between actual depth and theoretical depth can be ignored unless at very high altitude. If you shape the profile, do some minimum decompression on all dives and aren't pushing the limits. I don't think they mean to deny physics but prefer to compensate in ways other than theoretical depth tables or calculations. They may be right that a few feet of difference don't mean much unless you riding the "NDL" (whatever that is) doing square profiles.

 

[Atticus]

I don't mean to stir the pot, really.

This was discussed at TDS and in PM's, re: the GUE course at Tahoe. I believe the final verdict was that for the dives they were doing they preferred to not bring up the subject of altitude compensation. Some went on to say that GUE does not teach altitude compensation.

In the end my understanding is that it was stated that for the dives that one class did they felt like they were within safety margins on their profiles and did not choose to introduce altitude compensation. They definitely do recommend altitude compensation however.

I regularly do decompression dives at 6200' and with V-Planner the profile differences are significant. I am a believer in altitude compensation.

 

[Walter]

Am I misunderstanding or are you saying you are an instructor who doesn't understand altitude diving?

 

[DandyDon]

Don't think I understand the question...?

Elevation for Pecos Airport Texas is 2,613 feet, and I guess that San Soloman Springs is above 2,000 feet as well, but I don't guess I've every done anything special there. Not even sure my Oceanic dive computer will register the altitude enough to convert to Freshwater, as it has a 1,000 variance, I don't think it kicks in to FW mode until it registers 2,000.

Santa Rosa NM is at 4,600 feet, I think, but since I drive in from 3,300 feet, and cross 4,600 once a couple hours before I get there, then drive down when I leave - I really don't think about it much either. I know that my puter will register in the 3,000 to 5,000+ foot range when I turn it on.

Did I touch anything you were dealing with...?

don

 

[scubajoe]

Thanks for the info.

No Walter I do understand altitude diving physics. What I don't understand is how some people choose to ignore it. See the above post. All of the local diving I do is at altitude.
I have used altitude correction on every local dive and will continue to do so. My concern is that some are ignoring physics and advocating that to others.

Joe

 

[MikeFerrara]

scubajoe once bubbled...
Thanks for the info.

No Walter I do understand altitude diving physics. What I don't understand is how some people choose to ignore it. See the above post. All of the local diving I do is at altitude.
I have used altitude correction on every local dive and will continue to do so. My concern is that some are ignoring physics and advocating that to others.

Joe

Joe,

I think we'd get further discussing your concerns if you just said who is doing what.

 

[DandyDon]

Or didn't understand the question?

San Soloman - where I did some of my training and Joe trains others - is an altitude dive, but only 20 feet deep, so nothing was ever said.

Santa Rosa's Hole - where I've trained and Joe trains others - at 4,600 feet is a signifcant altitude dive, with 84 feet to grate adjusted to an equivalent depth of 100 feet. I plan the dive with my computer, like I do all my dives - so I'll become more familiar with the computer, but I study the RDP and the Wheel at times, to be aware of what's happening. Anyway, the puter is reading the altitude within 1,000 feet variance, and adjusting for freshwater, but there's no way I'm going to spend 20 minutes at the bottom.

don

 

[Dr Deco]

Hello Scuba Board Readers:

Some have observed that a degree of “sloppiness” can occur in the application of decompression procedures. The outcomes are still successful.

An Exact Science?

Decompression procedures are repeatable, and DCS can be made to appear with regularity, at least in the laboratory, if certain procedures are followed. It is necessary that exercise before, during, and after the exposure be controlled. Hydration levels are likewise important. This repeatability also applies to the appearance of Doppler bubbles as it does to DCS.

Because decompression schedules are made to eliminate DCS in the most susceptible diver, it often appears that the less susceptible divers can ”get away with anything.” At other times, if exercise or hydration is an issue, it will appear that one was “hit” while within the table (“undeserved”). The gods seem to be capricious.

The latitude in decompression procedures makes it difficult to determine if decompression schedules work for the reasons stated or if they are successful for other reasons. If you want to reach the surface safely and in minimal time, then it probably doesn’t matter. If you have an interest in the mechanism, it is important. The differences cannot be sorted out without research money to define a specific test. However, differences will probably surface given time; random events will result in the surfacing of “clues.”

Dr Deco :doctor:

 

[BigJetDriver]

Well said, Sir Powell. Your words are an excellent note of general caution to those of us studying the subject!