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O2 in tissues does not effect DCS because it is consumed by the tissues and doesn't persist, but O2 in the inspired gas does contribute the the total ambient pressure used to calculate bubble dynamics.
I suggest you re-read Baker's paper. I think you are mis-remembering it. He uses total ambient pressure in his GF calculations.
First the easy one:No, they compare total inert tissue pressure to the M-Value line to determine whether an M-Value has been exceeded. OK, moving on...
This is exactly correct. GF99 is 0 when tissue tension (dissolved inert gas pressure) equals ambient pressure. Not inspired inert pressure (which is FN2 * ambient pressure), but ambient pressure. When breathing O2 (inspired inert pressure of 0 at all depths), as an example, off-gassing continues, taking tissue tension down to 0 eventually, which is in negative GF99 territory as soon as tissue tension is lower than ambient pressure. Offgassing is driven by the *partial* pressure difference between tissues and inspired gas -- as Schreiner's equation states. It's not just O2, though -- breath any mix long enough and the GF99 will go negative.
True.
False, see Schreiner's equation. Off-gassing when tissue pressure is above inspired inert gas pressure. Again, inspired gas pressure is FN2 * ambient and will always be less than ambient pressure. Thus, off-gassing still occurs in the region where tissue pressure is between ambient pressure but greater than inspired gas pressure. Basically, GF99 has zero bearing on off-gassing.
Quite possibly. I'd say those who are using "GF" to mean the limiting "GF line" are correct. GF99, on the other hand, is dependent on tissue tension, the M-Value, and ambient pressure, and it has no dependence on the GF line. We then compare GF99 with the GF line to gauge stops on ascent.
@inquis I think you are spot on. What would be your response to the original question? Can you safely follow GF99 and forget about discrete deco stop as long as GF99 is always below your accepted conservatism? In my case I am diving most of the time 50/60 so I would make sure that GF99<60 all the time. Thank youWell, this thread has exploded.
No, they compare total inert tissue pressure to the M-Value line to determine whether an M-Value has been exceeded.
This is exactly correct. GF99 is 0 when tissue tension (dissolved inert gas pressure) equals ambient pressure. Not inspired inert pressure (which is FN2 * ambient pressure), but ambient pressure. When breathing O2 (inspired inert pressure of 0 at all depths), as an example, off-gassing continues, taking tissue tension down to 0 eventually, which is in negative GF99 territory as soon as tissue tension is lower than ambient pressure. Offgassing is driven by the *partial* pressure difference between tissues and inspired gas -- as Schreiner's equation states.
True.
False, see Schreiner's equation. Off-gassing when tissue pressure is above inspired inert gas pressure. Inspired inert gas pressure will always be less than ambient pressure. Thus, off-gassing still occurs in the region where tissue pressure is between ambient pressure but greater than inspired gas pressure. Basically, GF99 has zero bearing on off-gassing.
Quite possibly. I'd say those who are using "GF" to mean the limiting "GF line" are correct. GF99, on the other hand, is dependent on tissue tension, the M-Value, and ambient pressure, and it has no dependence on the GF line. We then compare GF99 with the GF line to gauge stops on ascent.
I know I'm coming in late, here. If anyone has already realized the above, I apologize. I'm having trouble keeping track given the volume/pace of the posts.
