The NOAA manual has it too. Come to think of it I think I have the Navy manual I'll look at it.
PADI Inadequacies
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Unfortunately, the PADI advanced OW manual (Adventures in Diving) only covers the bare essentials...very little in the way of theory and no mention of ascents to a higher altitude after the dive. As far as the encyclopedia is concerned...well...a couple of paragraphs and not of much help.
SA
When I referenced th PADI table I was thinking of theoretical depth charts. The encyclopedia gives an equation for calculating presure at altitude (an exponential) of course there are charts for this also. The NOAA manual has info for ascending after a dive but it is based on their dive tables. Do you have the NOAA manual? If you want one PM me. I have the Navy manual on CD but haven't looked at it yet.
Be right back...
Stephen Ash,
BRW's book Technical diving in depth has tables also along with a good explanation. I'm back at the shop now so I have access to my lib.
Anyone interested in the subject needs to read this.
BRW's book Technical diving in depth has tables also along with a good explanation. I'm back at the shop now so I have access to my lib.
Anyone interested in the subject needs to read this.
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Mike, so explain this to us. What does BRW have to say about ascending to altitude after an altitude dive?
SA
SA
I have to go look at a building but I can post more detail later.
In brief...Knowing the current rep group and the critical tension (scaled to altitude) of the controling compartment determines the max permissible group. If you have that the surface interval to drop into that group (from the tables) is the required SI before ascent. He then scales that SI from the US navy 120 min controling compartment to the 635 min controling compartment of the buhlmann tables to be consistant with the 24 hour before flying convention by multiplying the SI by 5.4...635/120 roughly.
Hope I got that right.
Theoretical depth conversions are as I described before.
In brief...Knowing the current rep group and the critical tension (scaled to altitude) of the controling compartment determines the max permissible group. If you have that the surface interval to drop into that group (from the tables) is the required SI before ascent. He then scales that SI from the US navy 120 min controling compartment to the 635 min controling compartment of the buhlmann tables to be consistant with the 24 hour before flying convention by multiplying the SI by 5.4...635/120 roughly.
Hope I got that right.
Theoretical depth conversions are as I described before.
I have BRW's Diving Above Sea Level. Mike's description sounds very similar to what this book. Actually it's ver batim.
I can do the math, I was just hoping I wouldn't have to. You know, you get use to the tables, and nice & easy, blah,blah....
What's missing are some practical worked out examples to go by. ;-0
I can do the math, I was just hoping I wouldn't have to. You know, you get use to the tables, and nice & easy, blah,blah....
What's missing are some practical worked out examples to go by. ;-0
Is this the author that lives in Los Alamos?
Theres altitude discussion going on in two places, so I apologize for duplicating this post.
First off I want to thank Stephen for the pointer to the NOAA ascent after diving table:
http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf
I had never seen that table before and its interesting, it probably represents what weve been doing for some time here in Colorado, though theres nothing scientific about what we do except that qualitatively we have a couple thousand guinea pigs a year doing dives and then driving over mountain passes. Many guinea pigs are brand new OW students that are completely unaware that theyre guinea pigs; the instructors lay out the day such that theyre OK, well, in most cases.
One of the more popular OW checkout sites around here is Blue Hole in Santa Rosa, New Mexico. BH is about 4k feet, but to get there you pass over Raton Pass which is 9k feet (Im rounding), so a 5k feet gain in altitude. The vast majority of shops do the checkout dives Saturday and Sunday and leave to head home on Sunday.
BHs maximum depth is about 80, which is a TOD of 110 as previously mentioned. The OW students dont get to that depth (or let me say arent SUPPSED to go to that depth) but already certified divers are down there mucking around the bottom (sometimes literally) quite often.
Shops setup late checkout from the hotels for the students, and the students are encouraged to go back to the hotel, shower (another discussion), take their time and then head out as a group, usually stopping in Las Vegas (New Mexico) for lunch (Pizza Hut, yuck theres a fantastic Mexican food place there that they ignore). Theory being to kill time before heading over Raton pass, about three hours driving from Santa Rosa. What very few instructors realize is that theres about a 3k gain in altitude from Santa Rosa to Las Vegas, which is only an hour away from Santa Rosa. Nevertheless, this seems to work fairly well, but its not perfect. Memorial Hospital in Colorado Springs sees about six DCS cases a year from divers returning from the hole. Taking a WAG double or triple that to take into account the number of DCS cases that are treated in Denver. My theory is that these divers actually get bent on the drive between Santa Rosa and Las Vegas, and Raton Pass really does them in Raton Pass being three hours away is pretty much a non-issue otherwise, despite the NOAA tables times (my guess).
So how does all this qualitative stuff translate to how we do out dives in Colorado, where sometimes we head over 11.2k passes on the way home? Answer: We guess a lot.
We dive the Navy tables and upon arrival do the 2 pressure groups for every 1k feet of ascension thing, as youd learn in altitude class. If were going to have to leave fairly quickly and/or the pass is close, well compute the dive at the altitude of the pass. This isnt without error, since were not out gassing at the rate wed be at that altitude, but as I said we do a lot of guessing. We also dive rich Nitrox mixes. At sea level Id probably standardize on 32% Nitrox, but up here we use mostly 36%. Our lakes arent very deep, so we dont have a lot of depth exposure (ignoring Blue Mesa, which is over 300 at the dam face
) and theyre cold enough that we dont stay very long. Those two factors work for us in limiting out exposure. After the dive we kill as much time as possible, usually stopping for something to eat before heading over the pass. Id guess that we always put at least two hours between the dive and the start of the pass ascent. So far so good and no DCS from any of the die-hards I know of that are doing these dives and passes.
Youre not going to get a definitive answer in this area. Just look at the flying after diving rules that are STILL being figured out even though thousands of divers fly every day. A couple thousand divers a year driving over passes after diving isnt even going to show up on DANs radar. Sorry I cant give you a nice, encapsulated this is what you need to do answer. Just be conservative and kill lots of time between the dive and the drive. Weve even thought about breathing O2 after the dive for some surface decompression, but so far it hasnt been worth the bother.
Also be aware that at one end of the continuum, GUE believes that the flying after diving (and therefore driving after diving) restrictions are complete BS. They have some persuasive arguments as well as data, but theyre all flatlanders, so thats beyond my comfort level.
Interesting aside a couple of the lakes we dive are so high that in theory we could go on pure O2 at 30 it computes out to a 1.58 ATA of O2 at 30 at Turquoise Lake, if memory serves.
Roak
Ps. Theres a truck weigh station at the very top of Raton Pass. Outside the office theres a pay phone and on that pay phone theres a DAN sticker I put it there.
First off I want to thank Stephen for the pointer to the NOAA ascent after diving table:
http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf
I had never seen that table before and its interesting, it probably represents what weve been doing for some time here in Colorado, though theres nothing scientific about what we do except that qualitatively we have a couple thousand guinea pigs a year doing dives and then driving over mountain passes. Many guinea pigs are brand new OW students that are completely unaware that theyre guinea pigs; the instructors lay out the day such that theyre OK, well, in most cases.
One of the more popular OW checkout sites around here is Blue Hole in Santa Rosa, New Mexico. BH is about 4k feet, but to get there you pass over Raton Pass which is 9k feet (Im rounding), so a 5k feet gain in altitude. The vast majority of shops do the checkout dives Saturday and Sunday and leave to head home on Sunday.
BHs maximum depth is about 80, which is a TOD of 110 as previously mentioned. The OW students dont get to that depth (or let me say arent SUPPSED to go to that depth) but already certified divers are down there mucking around the bottom (sometimes literally) quite often.
Shops setup late checkout from the hotels for the students, and the students are encouraged to go back to the hotel, shower (another discussion), take their time and then head out as a group, usually stopping in Las Vegas (New Mexico) for lunch (Pizza Hut, yuck theres a fantastic Mexican food place there that they ignore). Theory being to kill time before heading over Raton pass, about three hours driving from Santa Rosa. What very few instructors realize is that theres about a 3k gain in altitude from Santa Rosa to Las Vegas, which is only an hour away from Santa Rosa. Nevertheless, this seems to work fairly well, but its not perfect. Memorial Hospital in Colorado Springs sees about six DCS cases a year from divers returning from the hole. Taking a WAG double or triple that to take into account the number of DCS cases that are treated in Denver. My theory is that these divers actually get bent on the drive between Santa Rosa and Las Vegas, and Raton Pass really does them in Raton Pass being three hours away is pretty much a non-issue otherwise, despite the NOAA tables times (my guess).
So how does all this qualitative stuff translate to how we do out dives in Colorado, where sometimes we head over 11.2k passes on the way home? Answer: We guess a lot.
We dive the Navy tables and upon arrival do the 2 pressure groups for every 1k feet of ascension thing, as youd learn in altitude class. If were going to have to leave fairly quickly and/or the pass is close, well compute the dive at the altitude of the pass. This isnt without error, since were not out gassing at the rate wed be at that altitude, but as I said we do a lot of guessing. We also dive rich Nitrox mixes. At sea level Id probably standardize on 32% Nitrox, but up here we use mostly 36%. Our lakes arent very deep, so we dont have a lot of depth exposure (ignoring Blue Mesa, which is over 300 at the dam face
) and theyre cold enough that we dont stay very long. Those two factors work for us in limiting out exposure. After the dive we kill as much time as possible, usually stopping for something to eat before heading over the pass. Id guess that we always put at least two hours between the dive and the start of the pass ascent. So far so good and no DCS from any of the die-hards I know of that are doing these dives and passes.Youre not going to get a definitive answer in this area. Just look at the flying after diving rules that are STILL being figured out even though thousands of divers fly every day. A couple thousand divers a year driving over passes after diving isnt even going to show up on DANs radar. Sorry I cant give you a nice, encapsulated this is what you need to do answer. Just be conservative and kill lots of time between the dive and the drive. Weve even thought about breathing O2 after the dive for some surface decompression, but so far it hasnt been worth the bother.
Also be aware that at one end of the continuum, GUE believes that the flying after diving (and therefore driving after diving) restrictions are complete BS. They have some persuasive arguments as well as data, but theyre all flatlanders, so thats beyond my comfort level.
Interesting aside a couple of the lakes we dive are so high that in theory we could go on pure O2 at 30 it computes out to a 1.58 ATA of O2 at 30 at Turquoise Lake, if memory serves.
Roak
Ps. Theres a truck weigh station at the very top of Raton Pass. Outside the office theres a pay phone and on that pay phone theres a DAN sticker I put it there
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