Hello,
I just worked my way through the 2 amazing books of Powell and Salama (Deco for divers, and deep into deco) and had a blast of reading (and trying to understand) them.
There is a part in each book where I can't wrap my head around, and it takes about 3+ more weeks until I can meet up with my tech instructor to poke him with questions, so might as well try and dig for enlightenment here.
1.) First part is on page 20 of Salama's book, the chapter about Workman.
"If a diver on air (79% nitrogen) can stay indefinitely at a 10m depth and not get bent upon surfacing (this assumption later was found to be inaccurate), will this hold true if,..."
My question is about the part in bold. Inaccurate in what regard? Sadly I couldn't find a reference in the book (nor in Powell's book) on why, and when spinning up google or looking through any notes I got, it seems to be "commong knowledge" that one could indeed stay at <10m indefinitely on air and surface without getting bent. (IIrc Powell's (?) book mentions an experiment where divers at one point stayed an extended time at 10m and some got bent, so there is some empirical evidence that 1.58 pp = can surface any time doesn't hold true. But no explanation was given, would need to reread and find that part again.)
My assumption would be that fast tissues can tolerate a higher level of supersaturation and that if (for whatever reason) a person were to stay at 10m until all compartments were fully saturated, 1.58 npp would be considered too much supersaturation for the slower compartments?
2.) Powell's book, the chapter about Trimix decompression.
The general rule of thumb states that for dives <2 hours traditional deco models produce a longer deco time when using helium.
"For dives with a bottom time of less than 2 hours the progression is: Nitrox > Air > Trimix > Heliox"
That part I understand. What I don't understand is the progression of deco times if the bottom time happens to be >2 hours.
"As the bottom time reaches 2 hours the overall decompression time converges and then for dives over 2 hours bottom time the order is reversed with helium based mixtures giving shorter overall decompression time: Heliox > Trimix > Air > Nitrox"
Why would Nitrox lead to a longer decompression time than air? Is that due to a bigger gradient when switching to a rich nitrox deco mix from the bottom gas air, than when switching to a rich nitrox mich from "regular" nitrox?
Hope my questions make sense.
Thx.
I just worked my way through the 2 amazing books of Powell and Salama (Deco for divers, and deep into deco) and had a blast of reading (and trying to understand) them.
There is a part in each book where I can't wrap my head around, and it takes about 3+ more weeks until I can meet up with my tech instructor to poke him with questions, so might as well try and dig for enlightenment here.
1.) First part is on page 20 of Salama's book, the chapter about Workman.
"If a diver on air (79% nitrogen) can stay indefinitely at a 10m depth and not get bent upon surfacing (this assumption later was found to be inaccurate), will this hold true if,..."
My question is about the part in bold. Inaccurate in what regard? Sadly I couldn't find a reference in the book (nor in Powell's book) on why, and when spinning up google or looking through any notes I got, it seems to be "commong knowledge" that one could indeed stay at <10m indefinitely on air and surface without getting bent. (IIrc Powell's (?) book mentions an experiment where divers at one point stayed an extended time at 10m and some got bent, so there is some empirical evidence that 1.58 pp = can surface any time doesn't hold true. But no explanation was given, would need to reread and find that part again.)
My assumption would be that fast tissues can tolerate a higher level of supersaturation and that if (for whatever reason) a person were to stay at 10m until all compartments were fully saturated, 1.58 npp would be considered too much supersaturation for the slower compartments?
2.) Powell's book, the chapter about Trimix decompression.
The general rule of thumb states that for dives <2 hours traditional deco models produce a longer deco time when using helium.
"For dives with a bottom time of less than 2 hours the progression is: Nitrox > Air > Trimix > Heliox"
That part I understand. What I don't understand is the progression of deco times if the bottom time happens to be >2 hours.
"As the bottom time reaches 2 hours the overall decompression time converges and then for dives over 2 hours bottom time the order is reversed with helium based mixtures giving shorter overall decompression time: Heliox > Trimix > Air > Nitrox"
Why would Nitrox lead to a longer decompression time than air? Is that due to a bigger gradient when switching to a rich nitrox deco mix from the bottom gas air, than when switching to a rich nitrox mich from "regular" nitrox?
Hope my questions make sense.
Thx.