Riding GF99 instead of mandatory/safety stops

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I think you're confusing GF with GF99. As Dmaziuk has already pointed out GF increases from GFLo to GFHi. It never decreases. You keep saying total ambient pressure. The total ambient pressure in the inspired gas includes both N2 (and possibly He) and O2. O2 does not contribute to DCS.
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.

It is consumed by the body. All the equations I've worked with use inert gas pressure. Go read Baker's paper "decolessons" if you don't believe me. I'll gladly change my viewpoint if you can find a document that says otherwise.
I suggest you re-read Baker's paper. I think you are mis-remembering it. He uses total ambient pressure in his GF calculations.
 
Go read Baker's paper "decolessons" if you don't believe me. I'll gladly change my viewpoint if you can find a document that says otherwise.
All Haldaen deco models, not just Baker's GFs, compare total inert tissue pressure to to total total ambient pressure in determining whether an M-value has been exceeded.
 
Bakes's Decl lessons:
pg.3​
"Traditional M-values are given as P = m(Pamb) + Mo [y = mx + b form], where P = tolerated inert gas partial pressure, m = slope, Pamb = ambient pressure, and Mo = intercept at sea level."​

Baker: Understanding M-values :
pg.1​
M-values established the concept of a linear relationship between depth pressure [or ambient pressure] and the tolerated inert gas pressure in each "tissue" compartment.​
pg.2​
This included M-values which expressed a linear relationship between ambient pressure and tolerated inert gas pressure in the hypothetical "tissue" compartments.​
pg.3​
P = ambient pressure (absolute)​
... (more of the same)​
pg.7​
The Percent M-value Gradient calculation is a measure of how far a decompression profile has entered into the "decompression zone." 0% M-value Gradient is at the ambient pressure line and represents the bottom of the decompression zone.​
 
Would it make you feel better if we multiplied all M-values by .79 and compared them to P_amb * 0.79?
 
Well, this thread has exploded. :) First the easy one:
All Haldaen deco models, not just Baker's GFs, compare total inert tissue pressure to to total total ambient pressure in determining whether an M-value has been exceeded.
No, they compare total inert tissue pressure to the M-Value line to determine whether an M-Value has been exceeded. OK, moving on...
Off gassing can occur with GF99 < 0% if the inspired partial pressure of inert gas is < the tissue partial pressure.
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.
The GF99 is the % value between ambient pressure (which is 0%) and the m-value at that depth (100%) for the controlling tissue compartment (CTC).
True.
Off gassing can only occur when the CTC pressure is above the ambient pressure which is the inspired gas pressure.
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.

I think you're confusing GF with GF99. As Dmaziuk has already pointed out GF increases from GFLo to GFHi.
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.
 
Well, this thread has exploded. :) First the easy ones:

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.
@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 you
 
No, they compare total inert tissue pressure to the M-Value line to determine whether an M-Value has been exceeded.
I should have said "M-value at a the total ambient pressure" rather than "total ambient pressure".

The M-value (and the GF) is calculated from depth pressure, not depth inert partial pressure.
 
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