To: Randy
From: Phil
Subject: High Altitude Diving

Can you help me with some high altitude research?

To: Phil
From: Randy
Subject: High Altitude Diving

Altitude diving- Phil - take a look at the book "High Altitude Diving" by B.R. Wienke. We got the publication a few years back at a seminar, check page 20. I think your putting on more depth/time restrictions than is necessary. Going over is no problem, no correctons other than the altitude/depth and repetive group correction for the dive site elevation. Coming back we will be gaining altitude after diving, so at the top of the mountain pass we would have less pressure and outgassing may be to fast. The table on page 20 shows the minimum repetive group for various altitude changes after diving. This is what we need to pay attention to.

To: Randy
From: Phil
Subject: High Altitude Diving

With a depth of 7 feet maximum, you round up to 10 feet and at 4,000 feet, it is 12 feet and you then round up to 35 feet using the PADI tables, and stay down a maximum of 205 minutes.

Or with a depth of 7 feet maximum, you round up to 35 feet using the PADI tables, then round up to 40 feet on the high altitude chart and at 4,000 feet it is equivalent to 46 feet and round up to 50 feet and stay down a maximum of 80 minutes.

Or take the difference at 10 feet and 4,000 feet you add +2 feet to the 7 feet actual which equals 9 feet then round up to 35 feet using the PADI tables, and at 35 feet and you can stay down 205 minutes so need to revise the no decompression limits to 80 minutes at a minimum instead of what was stated on the form early and also that would be the maximum bottom time.

To: Phil
From: Randy
Subject: High Altitude Diving

This is all fine and dandy, but it still does not address ascending to altitude after a dive. Another book that explains the whole senerio is NAUI "Advanced Diving Technology and Techniques" page 150 to 156, by M. Murphey. Brent should have both of these publications if your interested. What table or book are you using to come up with your calculations ? Just interested, because we all should be using the same formulas and tables.

To: Randy
From: Phil
Subject: High Altitude Diving

We should plan the dive as if we are at the elevation of the pass, which would limit bottom time especially at the greater depths.

What table or book are you using to come up with your calculations?

I use the PADI recreational dive planner and the high altitude tables based on the E.R. Cross (1970 Skin Diver Magazine).

Just interested, because we all should be using the same formulas and tables.

Agreed we should be using the same materials.

To: Phil
From: Randy
Subject: High Altitude Diving

Phil-I am faxing down the altitude section from advanced diving techniques. I also have the E.R. Cross tables you refer to, they are to correct your depth gage/down time at the dive site. They do not take into consideration traveling to a site before a dive or going to a higher elevation after a dive. The new PADI recreational dive planner/tables only came out a few years ago, and has different repetitive groups than the Navy tables or the old PADI tables and are not compatible with most altitude tables. Maybe we can get our heads together in Redding and figure this thing out for sure.

To: Randy
From: Phil
Subject: High Altitude Diving

I also have the E.R. Cross tables you refer to, they are to correct your depth gage/down time at the dive site. They do not take into consideration traveling to a site before a dive

correct,

so using the PADI recreational dive planner, when you cross the pass, that is the start of a surface interval, so for every 1,000 feet you go up in altitude you count up two repetitive group letters.

So if you go up 1,000 feet you become a "B" diver, so you than have residual nitrogen in your body (theorically) and assume the drive to elevatiuon is a dive and you then start after you drive over the pass as a "B" diver and work the tables from there.

Then the rest of the time you are at the lake you use the elevation of the lake as the adjustment, as long as you stay at that elevation for 6 hours.

Then on the next day you drive home and you use the pass elevation instead of the lake elevation to figure your presure groups, but because you stayed at that elevation greater than 6 hours you do not have any additional penalty due to driving to the lake, you did that the day before.

But, for say, Lewiston, stay in Redding which is less than 1,000 feet drive to Lewiston (1,900 foot elevation) over a pass 4,000 feet in elevation then dive then drive home, use the 4,000/1,000 = 4 x 2 pressure groups/1,000 feet = 8,

so you start out at PADI RDP as an "H" diver, say at 8:30 am then after 1 hour and 48 minutes you are an "A" diver with a Residual Nitrogen Time (RNT) of 7 minutes with an allowable Bottom Time (BT) of 73 minutes.

or going to a higher elevation after a dive.

So you plan your dive as if you are diving at the highest elevation you plan to cross on the way home.

The new PADI rec dive planner/tables only came out a few years ago, and has different repetitive groups than the Navy tables

correct

or the old PADI tables

correct

and are not compatible with most altitude tables.

If you are going to use the Repetitive Group Letters to make your calculations

Maybe we can get our heads together in Redding and figure this thing out for sure.

Can do!

To: Phil
From: Z.B.
Subject: High Altitude Diving

I think Randy's first paragraph states the situation pretty well, except of course that PADI, which I'm more familiar with, doesn't use the same methodology on going to altitude, and as somebody said the pressure groups are not translatable from one system to the other.

I would chime in with one piece of information. At 4,000 feet the air pressure is reduced below sea level, but without checking I'm pretty sure it still exceeds 7 FFW (feet fresh water). Now Haldane's original hypotheses that dive tables were based on was, that you can halve the pressure in any tissue and not get bubbles. While this hasn't survived into modern theory, the surfacing ratios (that I think you'll find, among other places, in Wienke are not a lot less than 2:1 - as I recall). What I'm getting at is, I think, if you looked into it you could saturate at 7 feet, pop immediately to 4,000 feet and not get bent. Would I do it? Maybe after some thought, its not too dissimilar to the Burgdorf dive (such as it was), except the difference between the dive site and the pass there is much less.

With that said, let's get back to the more interesting theoretical aspects of this discussion:

The problem seems to be of two (or three) parts. Getting there, planning the dive, getting home. I'm not clear if you're staying the night at the dive site.

Getting there - like Randy said, on the way in the pass doesn't mean squat, other than its scenic and relaxing (or you're following the Winnebago from hell and its frustrating).

Planning the dive - in the PADI system I'd do this like you said, two pressure groups per thousand feet of DIVE SITE ELEVATION, thats my starting pressure group. If you knew the route rose steadily to the pass and descended steadily to the lake you COULD start your surface interval on teh way up the pass in the morning as soon as you reached the elevation of the lake, thats kind of subject to different weather fronts on different sides of the mountain. At the very least I'd start timing from the top of the pass down, unless the road dips below lake elevation.

Now, if you're spending the night there its pretty straight forward, you know your arrival group, you outgas per the PADI RDP and you correct all depths for the lake altitude. If you outgas to below A on arrival you can just dive your computers.

Now getting home. Here I think I saw some misunderstanding about dear old E.R. Cross. The Cross tables correct depth for altitude, but there is something I've seen called the Cross Correction. It says that for a SINGLE non-repetative dive after which you go to altitude you can safely plan it by calculating the dive as if it was being done at the highest altitude to be reached in 24 hours (if you're acclimated to the lake elevation you wouldn't make an arrival group calc. You could for paranoia however I guess). Now this has been shown to not be safe for flying since the ascent to altitude is thought to be too rapid, so how steep is your road? I don't like it, but have used it, within the limits making a single dive.

I don't have a planning tool for repetitive dives and then gong to altitude. I don't trust calculating the dives as if they were at 4,000 feet since you're doing repetative dives. With the depth involved; ie 7 feet, I think I'd do it after I looked at surfacing rations from 7 feet at 1,000 feet elevation to atmospheric pressure at 4,000 feet elevation.

Anyway, thats my two cents worth.

Z.B.

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