Question about using SurfGF...

[atdotde]

The main reason the surface GF is higher than the current is that the m value is depth dependent, the deeper the higher the tolerated excess pressure is. Since the GF is a fraction of the M value, bigger M value means smaller GF.

 

[dmaziuk]

I guess it depends on whether exceeding your NDL means 1) you exceed a certain max value (then use Pi<=M0), or 2) you equal or exceed the max value (then use Pi<M0).

??

Exceeding your NDL means P_{dissolved inert gas in tissue compartment} > M_{for tissue compartment}. When that happens you're no longer on a no-stop dive and there is no need to use Baker's formula to compute NDL.

When P_{inert gas in breathing mix} < M_{surfacing for tissue compartment}, that tissue compartment can never on-gas to its M_{surfacing for tissue compartment} and therefore will never exceed its NDL. That is the check I am talking about.

Mathematically you need those checks because the formula involves taking a logarithm of a fraction calculated from P_{dissolved inert gas in tissue compartment}, P_{inert gas in breathing mix}, and M_{surfacing for tissue compartment}. The fraction must evaluate to a positive number <= 1. Or else you'll get your NDL in imaginary numbers, time will run backwards, all kinds of bad stuff.

 

[UWSojourner]

??

Exceeding your NDL means P_{dissolved inert gas in tissue compartment} > M_{for tissue compartment}. When that happens you're no longer on a no-stop dive and there is no need to use Baker's formula to compute NDL.

When P_{inert gas in breathing mix} < M_{surfacing for tissue compartment}, that tissue compartment can never on-gas to its M_{surfacing for tissue compartment} and therefore will never exceed its NDL. That is the check I am talking about.

Mathematically you need those checks because the formula involves taking a logarithm of a fraction calculated from P_{dissolved inert gas in tissue compartment}, P_{inert gas in breathing mix}, and M_{surfacing for tissue compartment}. The fraction must evaluate to a positive number <= 1. Or else you'll get your NDL in imaginary numbers, time will run backwards, all kinds of bad stuff.

Assuming P0 < M, if Pi = M then that tissue compartment can never on-gas to M either. P will asymptotically approach M but never technically get there. You certainly can't exceed M.

Therefore, when P0<M you can check Pi <= M and, if true, then you can set the NDL to 999 (or whatever number indicates you'll never reach it).

 

[dmaziuk]

When a programmer goes to bed he puts a glass of water on his night table in case he wakes up thirsty, and an empty glass in case he wakes up not thirsty.

I guess there can't be an edge case where your conditions are met and the fraction evaluates to anything other than > 0 and <= 1. But I had to find a pen and a piece of paper and do very some basic symbolic math to see that.

 

[KenGordon]

When a programmer goes to bed he puts a glass of water on his night table in case he wakes up thirsty, and an empty glass in case he wakes up not thirsty.

I guess there can't be an edge case where your conditions are met and the fraction evaluates to anything other than > 0 and <= 1. But I had to find a pen and a piece of paper and do very some basic symbolic math to see that.

The cool kids will tell you that that is a very old fashioned view of the world and that these days the glass is both empty and full at the same time. However, they can only have 53 such glasses and mostly just resort to making outrageous claims about them to scare crypto people.

 

[dmaziuk]

Only while one's asleep. Waking up collapses the wave function and then it's the good old binary either-or. Of course, many of them cool kids these days seem to walk through life without ever attaining wakefulness, so their view of the world is also true.

 

[hammet]

Only while one's asleep. Waking up collapses the wave function and then it's the good old binary either-or. Of course, many of them cool kids these days seem to walk through life without ever attaining wakefulness, so their view of the world is also true.

Great. Now were talking quantum mechanics. Talk about getting out scienced from one's own thread.
sheesh.

 

[dmaziuk]

Great. Now were talking quantum mechanics. Talk about getting out scienced from one's own thread.

It's very apropos though: SurfGF at depth, like NDL, is based on things that have not happened yet and therefore exist only in the state of quantum flux. Once you're on the surface, then you'll know what your SurfGF actually is, but until then it's all quantum magic.

 

[hammet]

It's very apropos though: SurfGF at depth, like NDL, is based on things that have not happened yet and therefore exist only in the state of quantum flux. Once you're on the surface, then you'll know what your SurfGF actually is, but until then it's all quantum magic.

So what you're saying is that my NDL is in a superposition of all possible NDLs and only upon observation at the surface is the state determined? Does this involve quantum entanglement with my buddy by any chance?

 

[EFX]

SurfGF tells me my GF if I were to be instantly transported to the surface. It was my original assumption that that value represented a theoretical maximum GF value since because in reality, as I ascend, I would be off-gassing during the ascent so the actual GF that I would have after surfacing could be no higher than the value that I had read at depth.

However, as we know from learning about deep stops, it is possible to still on-gas in some compartments even though you have ascended from your maximum depth. Therefore, I am wondering, is it not possible that you could surface with an actual GF at the surface that is GREATER than the value you read before you started your ascent which would in a sense defeat the purpose of knowing your SurfGF at depth?

What I have seen so far in the latest version of my spreadsheet which has separate columns for current GF and surface GF is that the current GF upon surfacing is always higher than the surface GF at some depth. What's important to keep in mind is that any reading of CurGF or SurGF is for that particular point in the dive profile. Therefore, the SurGF at depth has no bearing on the actual CurGF, or for that matter SurGF, on arrival at the surface. For both CurGF and SurGF the general trend is that GF increases as the dive progresses to shallower depths. Within this trend the GF jumps to a higher value from a level segment to an ascent segment. This makes sense since with ascent there is a change in pressure in the leading (as well as other) tissue compartments which leads to greater off gassing.

Here are some values from the spreadsheet for three dives for the CTC (controlling tissue compartment), all to 100 ft for 30 minutes, with a descent rate of 60 fpm, an ascent rate of 30 fpm, a GF of 70/90, no second main gas, no deco gases, and a SI of 7 days. Negative values show the CTC ongassing, the value being a % of ambient pressure. Positive values show the CTC is off gassing and above ambient pressure. 100% is at the m-value line. Seg = dive segment, Dep = depth, CurGF = current GF, SurGF = surface GF. All are deco dives where the segment Sur = surface, Des = descent, Asc = ascent, Lev = level, and Stp = deco stop. The first dive is 21/0 (O2/He) Air, the second 21/79 Heliox, and the third is 21/40 Trimix:

Seg Dep CurGF SurGF
Sur 0 -100 -100
Des 100 -39 -39
Lev 100 -86 -86
Asc 30 40 62
Stp 30 36 59
Asc 20 58 70
Stp 20 50 67
Asc 10 80 84
Stp 10 49 62
Asc 0 88 88
Sur 0 -100 -100 (SI)

Seg Dep CurGF SurGF
Des 100 -39 -39
Lev 100 -98 -98
Asc 40 46 69
Stp 40 38 68
Asc 30 64 79
Stp 30 50 71
Asc 20 78 85
Stp 20 43 67
Asc 10 83 88
Stp 10 36 57
Asc 0 89 89
Sur 0 -100 -100 (SI)

Seg Dep CurGF SurGF
Des 100 -39 -39
Lev 100 -89 -89
Asc 30 44 65
Stp 30 37 63
Asc 20 63 76
Stp 20 46 66
Asc 10 80 85
Stp 10 44 60
Asc 0 87 87
Suf 0 -100 -100 (SI)