Ascent to altitude

[aquaregia]

So I'd been planning a trip to Croatia for a while and asked about the altitude on the way back. I was informed it wasn't a problem because of the tunnels. Then my plans changed and I went to Italy. I figured it would be about the same.

After three days of pushing NDLs on nitrox, I decided to drive straight home. I figured I'd download an altitude app for my iPhone for peace of mind. I got to Milano and discovered I was already at 1000'. After calling a bunch of people I knew, including DAN (turns out Googling random city names along the road isn't part of their job ), I figured I'd wait another hour or so and go for it. My computer was showing 8hrs of no-fly time remaining, so my plan was to watch the iPhone and stop if it hit 1500'.

So I drive along, I see it hit 1500' and I dutifully stop. Then it hits 1600'. Then 1700'. It finally stopped rising at 2100' after several minutes. Looks like someone put quite the smoothing algorithm on that thing. At that point, I knew that about 20km ahead it would drop back down to 1000', so I figured I'd get it over with.

I spent the entire drive being convinced that I had new rashes (nope, skin's always been that way), that I was itchy (likely sweat on hair follicles), that my left wrist was aching (my left wrist is *always* aching), etc. I had a bottle of water, so I figured I'd drink that, rehydrating being pretty much the only thing I could do preventatively (other than turning around and going back to Italy, but the exits were not kind on that front). I tell you though, when I opened up the bottle of sparking water at 2000' and it foamed and went everywhere I definitely swore. No actual problems though.

For future reference, Saint Gotthard tunnel hits just shy of 3800' (1150m).

 

[boulderjohn]

DAN's recommendations of altitude gain after diving assumes that it is immediately safe to ascend 2,000 feet. Here is the NOAA ascent to altitude table. You may find it useful as well.

 

[bleeb]

Here is the NOAA ascent to altitude table. You may find it useful as well.

Note that to use the NOAA Ascent to Altitude Table, you need to use the pressure letter groups from the NOAA dive tables (no-deco air table, Nitrox 32 or Nitrox 36).

 

[fisheater]

Also, as far as immediate treatment/prophylaxis goes, in addition to water, lower elevation and - of course - oxygen, an aspirin may assist in the off-gasssing process.


Sent from my iPhone using Tapatalk

 

[aquaregia]

DAN's recommendations of altitude gain after diving assumes that it is immediately safe to ascend 2,000 feet. Here is the NOAA ascent to altitude table. You may find it useful as well.

I considered doing that, but the dives were so far off the tables that even guessing average depths, etc, would have been pretty handwavey.

 

[bleeb]

I considered doing that, but the dives were so far off the tables that even guessing average depths, etc, would have been pretty handwavey.

I'd like to explore this issue a bit more. Approaching NDLs over multiple days, possibly coupled with use of dive computers (reduced nitrogen loading resulting from multi-level diving, as opposed to the square profiles assumed by tables) is not an uncommon situation. As aquaregia mentioned, this might be exceeding what tools like the NOAA altitude table can directly handle. In such a situation, are there other tools, calculations or techniques out there that might at least give an idea if someone might be pushing the limits?

 

[aquaregia]

Sure, so here's some relevant info, and I'll follow it with my thought process:

Day 1: 115' for 0:50 on 30%
Day 2: 110' for 0:60 on 32% after 22hr SI
Day 3: 110' for 0:80 on 32% after 18hr SI

All dives we went straight down to 110' stayed there until computer was around NDL (ballpark it at 25min) then ascended over the remainder of the dive, with a slight bias towards the surface. I'll guess the average depths as 85', 80' and 70'. The first dive was on 30% not 32%, so that'll make it about 90' E(EAN32)D.

NOAA 32%: 90' for 0:50 => K, SI => A
NOAA 32%: 80' for 0:60 + 0:04 => L, SI => A
NOAA 32%: 70' for 0:80 + 0:05 => M
Altitude tables indicate 10:55 to 4000', 21:37 to 8000'

My computer gives me a calculated no-fly time, which was about 10 or 11 hours. This makes me think that I was a bit conservative earlier, which makes sense as those tables recommend substantial deco that my computer did not push for. So, if I look at an 8000' time of 10 or 12 hours, I'll guess that I was a G coming out, with a time to 4000' as only 1:15.

Given the way these things work, if you have a dive computer that calculates no fly (as I do) and wait an amount of time equal to the ratio between the max altitude and 8000', you're almost certainly fine. I guess only until you hit a the 24hr ceiling, which I have no idea if my computer does.

I do sort of suspect that this is like reefing sails: if you think you might be pushing the limits, you probably are.

 

[ajduplessis]

I asked an instructor the other day if he ever had the bends. He replied that it had only happen once. They were doing some deco dives in flooded mine and he was eager to get back home. He was aware of the big altitude increase on the way back but did not think it would make a difference. He immediately started to feel like he was getting the flu and a few minute later he could see the result on his skin. He stopped, put an O2 reg in his mouth and continued. Once on the descent on the other side he started to feel better.

Another mate of mine went diving in Sodwana. He had a friend that collected him in a Cessna four seater single engine prop straight after 2 morning dives. Shortly after take-off he got bend.

I do most of my dives at altitude (around 5000f) and take it very serious. I have seen divers doing altitude dives without adjusting the settings on the DC resulting in bends.

I am glad nothing happen to you.

 

[TSandM]

You know, if you think about it -- if you get symptomatic while DRIVING over a pass, you were bent before you went.

Airplanes cause trouble because their ascent rates are very rapid -- sea level to 8000 feet in a couple of minutes. It just isn't like that with a car. You have the surface interval of packing the gear, and then you have to drive. A 6% grade is an extremely steep highway hill, and few roads maintain that kind of climb for very long. Usually, you are talking about time in hours to get to 3000 or 3500 feet (for me, sea level to 3500 is an hour, if there's no traffic ). If you translate that into ascent rate in water, you realize how tiny a rate that is (it's only about 60 fpm in AIR).

 

[fjpatrum]

You know, if you think about it -- if you get symptomatic while DRIVING over a pass, you were bent before you went.

Airplanes cause trouble because their ascent rates are very rapid -- sea level to 8000 feet in a couple of minutes. It just isn't like that with a car. You have the surface interval of packing the gear, and then you have to drive. A 6% grade is an extremely steep highway hill, and few roads maintain that kind of climb for very long. Usually, you are talking about time in hours to get to 3000 or 3500 feet (for me, sea level to 3500 is an hour, if there's no traffic ). If you translate that into ascent rate in water, you realize how tiny a rate that is (it's only about 60 fpm in AIR).

There are places in CA where you can go from sea level to 6000+ feet in a matter of about an hour and a half, if you drive just barely over the posted speed limits. For those of us that don't mind zooming along, it's not really that difficult to get there even faster. If I dive at Folsom lake, Sacramento, for example, and then drive to Tahoe, I've got an elevation gain of about 6000 feet. I have done that drive in just about an hour.

That's not to say I disagree with you, TSandM, just wanted to make it clear that some places it's much easier to get more drastic altitude changes without much effort. In some places in Europe where the roads are older and less consistent in their gradation I'd be extremely careful while driving after diving close the the limits.