Thread: Diving Depths
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Old 04-01-2009, 06:13 PM
Eddie Eddie is offline
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Join Date: Mar 2009
Posts: 252

General Pain,

Jester's list is pretty accurate. Some nitpicks could be made but nothing warranting any real corrections. Most regulators now have dive computers that erase the need for dive tables. It tracks all dive data: depth, time, date, temperature, Nitrogen loading (absorption by your body), O2 loading for NITROX computers, ascent rate, beginning and ending pressures in some models, and a plethora of other information.

For the record, if his is not substantial to answer your questions, I just received my Advanced Open Water Certification on 22 MAR, and am getting NITROX certified this weekend, and have been diving since 2002. I'm fairly knowledgeable or at the very least know the right people to ask any questions you have.

He was right about NITROX. It extends your time at depth and allows you to go deeper.

By pressure chamber, are you meaning a decompression chamber? And, what context do you mean it in? A dive emergency or we just did our planned dive and we're now mandated to go into the DECO chamber for X hours?

If the first manner, you could possibly need the chamber from an ascent from 6 feet. Likely? No. From 50 feet? Much more likely. From 90 feet? Most likely (which happened to a girl in my Advanced Open Water class).

If you mean the second situation, no recreational dive depth (up to 130 feet) will require time in a DECO chamber unless you exceed the Allowable Bottom Time (ABT). As Jester said, the ABT is significantly shorter at deeper depths.

If your mercs are using rebreathers, they can't go below 33 feet, otherwise the oxygen becomes toxic. Below 33 feet (as in 32, 31, 30, etc, not below as in 90 feet), the nitrogen accumulation in the body is negligible and a person can effectively stay as long as he has air, i.e., your tank or rebreather will stop working before it's a danger to you.

For deep diving, you have some special considerations though. At depth, because of pressure, your air in the tank is going to be smaller in volume and the air in your lungs is going to be smaller in volume. You're going to continue breathing your normal breaths though to your full lung capacity. This means you're breathing more air at the same rate you breathe less air at the surface. Your tank goes faster, in otherwords.

Also, if you want to go below 130 feet, you get into what is called Tec Diving. With Trimix gases you can go well below 130 feet. This is extremely hazardous and requires multiple decompression stops along the way up (requiring surface support stations -- essentially extra sets of gear dangling on a buoy at fixed depths), but I don't know what the threshold for chamber time is. My advice, get something reasonable sounding, like 250 feet, and start fudging something from that.
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