Altitude after dives

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my computer and most i have seen auto compensate. I have not really change it. Though i am pretty sure that they conservative settings just bump up the latitude by 1000 ft. I could be wrong on that. I still do not see how that would predict what would happen when i ascend to a specific altitude. DCS is two fold. It is not just about how much nitrogen you have but also about how fast you change pressures. I have not been able to read all the info on that website to look at there logic or decide if it seems sound. I guess the reality is that the pressure changes in 1000ft is pretty low so it is more about the amount of nitrogen....... Got some stuff to learn and read.
 
Jimmy, keep in mind that the change in pressure from coming from diving depth (any depth) to the surface is an exponentially greater than the change in pressure on rising 2000 feet in elevation.

I think you are making a mountain out of a molehill.
 
yeah, I know. I just like better understanding the problem so i can make educated decisions about any risks i take. There are a lot of factors i can change in this situation, but the altitude is not one of them.
That NOAA chart is really interesting. The statement of "if you dive at or above 8k feet, you can fly when ever you want" It makes sense but i have never seen anyone say it before.
 
Wow, if you can get from the dive site to 2500 feet in an hour, you're fast! It takes me most of that time to get all my gear off and packed up in the car, and chit-chat with my buddies.

I regularly drive over a 3000 foot pass to go to work. It takes me an hour from my house to the pass, so typically at least two hours "surface interval" before I get there, and the ascent is gradual. The incremental drop in pressure is trivial. I do not worry about it. A friend discussed this with DAN years ago, and they told him the same thing.
 
my computer and most i have seen auto compensate. I have not really change it. Though i am pretty sure that they conservative settings just bump up the latitude by 1000 ft. I could be wrong on that. I still do not see how that would predict what would happen when i ascend to a specific altitude. DCS is two fold. It is not just about how much nitrogen you have but also about how fast you change pressures. I have not been able to read all the info on that website to look at there logic or decide if it seems sound. I guess the reality is that the pressure changes in 1000ft is pretty low so it is more about the amount of nitrogen....... Got some stuff to learn and read.

In my Suunto Vyper you set the altitude. So if I were travelling to 2500 ft I would set it to the 1000-5000 ft setting (the A1 Suunto setting). I think in the newer Oceanics you can also set the altitude, because it's one way of making the computer more conservative.

Look at it this way. The problem is slowly releasing the nitrogen load on the way up. The computer tells me how to ascend to the surface at 2500 ft atm pressure. But instead of the surface being at 2500 ft it's at 1000 ft, so you're effectively making the ascent in two steps instead of one, first to 1000 ft atmospheric pressure then to 2500 ft atm pressure. It's the same as adding another safety stop.

Adam
 
Maybe I've missed something, but when you surface from a 30m dive you've been at 4 ATM pressure at 30m then off gas at 1 ATM on the surface at sea level. If you then drive, lets say to a height where atmospheric pressure is 800 milli bar (that's 1,700m), or 20% less than atmospheric pressure at sea level, you're total pressure change is 3.2 ATM as opposed to 3 at sea level, an increase of less than 10 percent, in theory I supose it means that you off gas ten percent faster, and as we know you need to off gas slowly, but the difference is still only 10 percent. Add in the time it takes you to drive to a height of 1,700m and I cant see it making any difference. I'm aware that this is a public forum, so if I'm speaking a load of nonsene, please correct me, with some calculations as to where I've gone wrong.
Altitude.org | Altitude air pressure calculator give some useful figures
 
Maybe I've missed something, but when you surface from a 30m dive you've been at 4 ATM pressure at 30m then off gas at 1 ATM on the surface at sea level. If you then drive, lets say to a height where atmospheric pressure is 800 milli bar (that's 1,700m), or 20% less than atmospheric pressure at sea level, you're total pressure change is 3.2 ATM as opposed to 3 at sea level, an increase of less than 10 percent, in theory I supose it means that you off gas ten percent faster, and as we know you need to off gas slowly, but the difference is still only 10 percent. Add in the time it takes you to drive to a height of 1,700m and I cant see it making any difference. I'm aware that this is a public forum, so if I'm speaking a load of nonsene, please correct me, with some calculations as to where I've gone wrong.
Altitude.org | Altitude air pressure calculator give some useful figures

There's a flaw in your argument. There has to be otherwise there would not be the prohibition against flying after diving. Let me take your argument to the extreme. Dive to 20 atm then to sea level, and then make the same dive to surface at 0.5 ATM (around 5000m or 16,500ft). You would argue the two dives are almost identical because in the first the pressure change is 20 ATM and in the second it's 20.5 ATM.

According to your argument diving to altitude would only be important for shallow dives, where the percent difference in pressure is large.

Imagine a nitrogen bubble after coming up to the surface at sea level after a dive. If the dive is to altitude, the bubble expands from 1 ATM to the pressure at the altitude. In your example to 1700m the bubble expands to 1 atm/ 0.8 atm or 1.25, which is a further 25 % expansion in volume. The algorithm has to account for this further 25% expansion regardless of how deep the dive was.

Adam
 

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