Diving at altitude

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richhagelin

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i have done all my diving at sea level. I am about to do some diving in a lake at 2000 elevation. Any adjustments I need to make compared to diving at sea level?

Thanks for any advice.



Rich Hagelin
 
Our own @boulderjohn can offer an educated opinion on your question.
 
Do you mean 2,000 feet or 2,000 meters? The difference is huge.

There are lots of ways it could impact, or it could have very little impact. It all depends upon the kind of dives you plan to do.

At the top of the list on my Resources page is a comprehensive article on diving at altitude. You can read it all and look for your answers there, or you can ask more specific questions here. I will be happy to answer.
 
@richhagelin which computer are you using and will it automatically compensate for altitude? Most new ones will auto compensate for altitude or allow you to preset it. At 2000ft you'll be a bit less than 10% deeper than you think you are, i.e. when your computer says 40ft, you'll actually be about 43ft deep. Most modern computers will figure it out when you turn them on at altitude since they assume you turned them on at the surface. That said there can be a lot of weird anomalies when diving at altitude so you'll want to read John's articles and ideally the USN/NOAA opinions on it. I would not buy into the UTD decision that altitude is irrelevant
 
My computer doesn't change to altitude mode until 3001', so I'm hoping that's OK.


Bob
 
The first first couple thousand feet above sea level do not bring on many changes. If you are doing basic recreational dives and staying well away from NDLs, it won't make a lot of difference, either. If, as Tom suggests, you are using a computer that adjusts for altitude automatically, then it will take care of most of the differences for you. The most important factor is that when we are concerned about decompression sickness, what we are worried about is the difference in pressure between the tissues in our bodies and the ambient pressure around us when we approach the surface and get out of the water. At altitude, that ambient pressure is less, so there is a greater difference. The greater the altitude, the greater that difference.

I will give you an idea of the degree to which this can be true by describing a reverse altitude incident. Years ago, I had an old Suunto Cobra, which had to be adjusted for altitude manually. (I think Suuntos still have to be adjusted manually.) I had stopped using it in favor of a different computer. I don't remember that sequence of events that led to this, but I ended up taking that Cobra (which is air integrated) and using it as a pressure gauge on a 2-tank, recreational dive in Florida. About half way through the second dive, it occurred to me that the last time I had used that Suunto was in the Denver area, and I had it set to that altitude. I immediately took a peek and saw that according to the Suunto, which thought I was diving at altitude, I was well into decompression, while the computer on my wrist (which knew I was at sea level) said I wasn't even close.
 
Most modern computers will figure it out when you turn them on at altitude since they assume you turned them on at the surface.

From my manual:
Altitude:
• Operational from sea level to 14,000 feet (4,270 meters) elevation
• Measures ambient pressure every 30 minutes when inactive, upon activation, every 15 minutes while activated.
• Does not measure ambient pressure when Wet.
• Compensates for Altitudes above sea level beginning at 3,001 feet (916 meters) elevation and every 1,000 feet (305 meters) higher.

My older one (2002) had the same specs with the exception of compensating beginning at 2001'.

And yes everyone should be extremely familiar with their dive computer manual, lest they be as surprised as I was one day. (recorded elsewhere on the board)


Bob
 
https://www.shearwater.com/products/perdix-ai/

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