Posted: 4/24/2017 9:14:27 PM EDT
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Friend was just telling me about depth restrictions and we were talking about how altitude comes into play. He was saying that your rating is at sea level and if you go up in altitude your allowed depth is less.
I figured it would be the opposite with pressure being less. Please educate me as to why this is and pretend you're speaking to a third grader. |
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Higher the altitude the lower the pressure on your body when coming out of the water. Less pressure means less pressure keeping air bubbles from forming inside you. |
| Its like the carbon dioxide in a can of soda. When you come up from depth your body is under less pressure and the gas is allowed to separate itself. If you do this slowly, everything is good. If you do this too rapidly, or put yourself into an environment with an even lower environmental pressure like a plane cabin, there could be issues due to rapid gas separation into your blood. The risk is low given how most people dive, but it's not something you want to play around with. |
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This is true. If you dive don't fly for 24 hrs. If you get in a 737 after you do a dive, there is a real good chance you will not make it alive to the ground. I think cabins are pressurized to 8000 feet above see level. When we go on vacation we will typically do 4 or 5 dives a day. Do that for 5 days and get in a plane to come home you better take the last day and go shopping. If you ever come down with the bends you better make sure the rescue pilot knows to stay as low as possible or it may help to kill you faster. Think of it like this, shake up a bottle of coke and watch it. The bubbles go right back to a liquid. No take off the top. The bubbles quickly turn back into a gas. That is what happens in your blood then you have too much nitrogen in your blood and you hit the surface to fast or get in a plane. You must off gas the nitrogen. Quoted:
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Higher the altitude the lower the pressure on your body when coming out of the water. Less pressure means less pressure keeping air bubbles from forming inside you. |
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A whole different set of rules come into play when diving at altitude. Never done anything more than a 300 feet above sea level. They probably have dive computers to calculate this |
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Friend was just telling me about depth restrictions and we were talking about how altitude comes into play. He was saying that your rating is at sea level and if you go up in altitude your allowed depth is less. I figured it would be the opposite with pressure being less. Please educate me as to why this is and pretend you're speaking to a third grader. Assume an elevation of 2500 ft, and your target (planned) dive is 132 ft, your equivalent ocean depth would be 141 ft (atm at surface = .913). Your nitrogen level would reflect the adjusted and your NDL would be adjusted accordingly. In short you cannot dive for as deep or as long at depth at altitude as you can at sea level - 1000'. A single dive nets you a no fly for 12 hours. A two dive profile changes that to 18 hours. In 3rd grade language... less pressure at surface = adjusted depth and compensation for nitrogen absorption and the requirement to off gas. Or as my father would say... "Because I fucking said so." |
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This. Quoted:
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Higher the altitude the lower the pressure on your body when coming out of the water. Less pressure means less pressure keeping air bubbles from forming inside you. |
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Any dives over 1,000 feet above sea level need to be carefully planned and conducted. Be conservative and don't take chances or shortcuts.
Generally, unless you brought a hyperbaric chamber to the dive site with you, there won't be one around for a long distance to treat a DCS incident. If you're diving in the mountains, getting out of the mountains and time to treatment become very real issues. It may not be a big deal for your reason for diving, but with fresh water less dense than sea water, the depth gauges will be off by 1 foot per 33 feet of indicated depth - 33 feet on your depth gauge = 34 feet actual depth. I'm a commercial diver for almost 22 years and I wouldn't do any serious diving at altitude without serious planning first |
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Im not sure what your friend means by "your rating is at sea level." He is however correct. At elevation (defined as above 1000') there is a different dive table to be used. Your actual depth in the lake at altitude when calculated against its equivalent in ocean depth will be less. It isnt a drastic difference unless you are talking several thousand feet of elevation for a lake. Assume an elevation of 2500 ft, and your target (planned) dive is 132 ft, your equivalent ocean depth would be 141 ft (atm at surface = .913). Your nitrogen level would reflect the adjusted and your NDL would be adjusted accordingly. In short you cannot dive for as deep or as long at depth at altitude as you can at sea level - 1000'. A single dive nets you a no fly for 12 hours. A two dive profile changes that to 18 hours. In 3rd grade language... less pressure at surface = adjusted depth and compensation for nitrogen absorption and the requirement to off gas. Or as my father would say... "Because I fucking said so." |
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A whole different set of rules come into play when diving at altitude. Never done anything more than a 300 feet above sea level. They probably have dive computers to calculate this |