Best value location for PADI Certification
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zich6
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Ask @boulderjohn, I think he may even offer a class
Crossing a pass at 7500 feet after diving at 6,400 feet should not be an issue. It is generally believed that an ascent of less than 2,000 feet may be made at any time after diving. Although there is no good way to quantify it as far as I know, that 2,000 foot limit SHOULD also vary by starting altitude--a 2,000 feet ascent starting at sea level is more serious than a 2,000 foot ascent starting at 6,400 feet.
My resources page has some articles on diving at altitude and ascending to altitude after diving if anyone is interested.
Interesting. While there is no student manual for me to refer to (and I never looked at any IG), I do have a table somewhere. If my memory serves me at all (and this was over 3 years ago), I was supposed to wait 6 hours (which I never did) before attempting going over the passes.
I did get some strong headaches as a result.
I have never heard of a 6 hour rule for an ascent to altitude. Both NOAA and the US Navy have tables that can be used for ascending to varying altitudes after diving, but they require that you use the US Navy tables (or tables that follow them). They are on my resources page, and they are explained in more detail here.
John,
Thanks. I was looking at that. I’ll reach out to my instructor to find out the basis of what I remember (and my memory could be completely incorrect).
It could be a rule your instructor made up, and there is no harm in that. In fact, it is a necessity.
As I mention in my article, there is no really reliable information on ascents to altitude like that. Before I wrote my article, I consulted with several world-renowned experts on decompression theory and asked them to help me write it. They quite rightly and quite politely refused. There is no solid research on it, and they did not want to have their names associated with anything that looks like advice and is not founded on solid science. I decided to go ahead anyway, and my article is carefully worded to say that I am only providing access to resources that will help you make up your own mind and not in any way telling you what to do.
I regularly have to ascend to altitude after diving, often after a deep decompression dive. In order to do this, I have had to come up with my own personal set of rules based upon my own interpretation of those resources, and I have had to talk to my students about it. I tell them what I do, but I also tell them that what they do is their decision. Your instructor had to do the same thing, and perhaps the 6 hour rule was his personal decision. It could also be him repeating what he was told by someone else who also had to make such a decision.
So here is a controversial idea that is not in my article.
Let's say you use a computer like a Shearwater that keeps track of your tissue off-gassing during your surface interval. Let's say you have set your gradient factors in it to numbers with which you are sure you will be safe. During a decompression dive, you can look at a readout of how your tissues are doing in respect to those gradient factors as the computer tracks your ascent. It will continue to track that during your surface interval. That tracking is done in relation to ambient pressure, which depends primarily upon your altitude.
In theory, you can keep track of that and make sure you stay within safe gradient factors as you ascend in altitude, just as you would during an ascent on your dive. Asked about that, Shearwater would not commit to it, saying that before ascending to altitude, you should follow flying after diving guidelines.
Let's say you use a computer like a Shearwater that keeps track of your tissue off-gassing during your surface interval. Let's say you have set your gradient factors in it to numbers with which you are sure you will be safe. During a decompression dive, you can look at a readout of how your tissues are doing in respect to those gradient factors as the computer tracks your ascent. It will continue to track that during your surface interval. That tracking is done in relation to ambient pressure, which depends primarily upon your altitude.
In theory, you can keep track of that and make sure you stay within safe gradient factors as you ascend in altitude, just as you would during an ascent on your dive. Asked about that, Shearwater would not commit to it, saying that before ascending to altitude, you should follow flying after diving guidelines.
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