Half Life = "M" ?

[MikeFerrara]

O-ring once bubbled...
We can't go off letting Snoopy use neo-Haldanian crap now, can we? He will be doing all his stops at 10' and calculating his deco stops for the maximum overpressure gradients...he'll look like a can of soda..

O-ring,
Does GUE not teach their students to use D-plan. D-plan of course is Buehlmann ZHL-16B (gas obsorbtion!). Don't worry before we let Snoopy go off and rack up a bunch of deco we will tell him about gradient factor controled deep stops.

As a side note you can generate a profile that looks like a VPM profile by tweaking the gradient factors. For the dives we're doing 10, 90 will make a Buehlmann profile look like a VPM profile

 

[O-ring]

MikeFerrara once bubbled...


O-ring,
Does GUE not teach their students to use D-plan. D-plan of course is Buehlmann ZHL-16B (gas obsorbtion!). Don't worry before we let Snoopy go off and rack up a bunch of deco we will tell him about gradient factor controled deep stops.

As a side note you can generate a profile that looks like a VPM profile by tweaking the gradient factors. For the dives we're doing 10, 90 will make a Buehlmann profile look like a VPM profile

I haven't taken that class yet . I use decoplanner, but my gradient factors aren't set to 10,90

 

[Diver0001]

Snoopy once bubbled...
Hi

I am cross posting this from another diver's forum ....

<snip>

So the question:

Are the tissue HALF TIMES the "M" Values?
Why is it called "M", why not "X", why not "Y"...?
Did they determine the different tissue saturation points using goats?"

[\quote][\i]

M values stand for "Maximum" values, a term coined by a guy called Workman (I think). They represent some sort of theoretical saturation/tension limits for various hypothetical tissue compartments. I think M values and 1/2 times are related but different. In any case they both lend themselves to use in computer programs to calculate things like deco-ceilings and NDL's. It's tempting to see tissue compartments as something real but it's just a mathematical model. Nothing more.

As for the goats, it's true. A guy called John Haldane did some research into NDL's by bending goats. He didn't invent M values, though. His research was empirical. A guy called Buhlmann is generally credited with dreaming up M values sometime later.

R..

 

[MikeFerrara]

O-ring once bubbled...

I haven't taken that class yet . I use decoplanner, but my gradient factors aren't set to 10,90

Niether are mine.

 

[Drew Sailbum]

Regarding the PADI RDP:

2. The RDP model has 14 compartments ranging from
5 to 480 minute halftimes.
3. Surface interval credit is based on 60 minutes wash-out.
The WX, YZ rules make sure slower compart-ments
remain within accepted limits.

And regarding M-values:

3. Besides differing in halftimes, each compartment
has a different M-value.
a. M-value is the maximum tissue pressure allowed
in the compartment when surfacing to prevent
exceeding acceptable gradient. [Note: there’s
actually different M-values for each compartment
at each depth, but in no stop diving we only use
the one that applies to the surface.
b. The faster the compartment (shorter halftime),
the higher the M-value (the more nitrogen it is
allowed to have when surfacing); the slower the
compartment, the lower the M-value.
c. The M-value is determined by test dives showing
what does and does not result in DCS or Doppler-detectable
bubbles.

 

[Walter]

Calling the 60 minute compartment the controlling compartment is merely saying all compartments slower than 60 minutes are ignored. They are in the model on which the RDP is based. They are not part of the RDP.

A compartment clears 50% after the 1st time period, 75% after the 2nd, 87.5% after the 3rd, 93.75% after the 4th, 96.875% after the 5th, 98.4375% after the 6th. While compartments continue to clear with additional time, the change after the 6th time period is so small they are considered unimportant and each compartment is considered clear after 6 half time periods have expired. After 6 hours the 480 minute compartment is virtually unchanged. If there was a compartment slower than 60 minutes used in the RDP, it would be impossible for the RDP to clear in 6 hours.

 

[padiscubapro]

Walter,
Here is the actual values PADI uses to create their model.

The DSAT Recreational Dive Planner (PADI) model (1987)
No. ô (min) M0 (msw)
1 5 30.42
2 10 25.37
3 20 20.54
4 30 18.34
5 40 17.11
6 60 15.79
7 80 15.11
8 100 14.69
9 120 14.41
10 160 14.06
11 200 13.84
12 240 13.69
13 360 13.45
14 480 13.33

 

[Walter]

I'm aware the model has slower compartments. The RDP ignores them.

 

[Drew Sailbum]

Walter once bubbled...
Calling the 60 minute compartment the controlling compartment is merely saying all compartments slower than 60 minutes are ignored. They are in the model on which the RDP is based. They are not part of the RDP.

Huh? The 60 minute compartment is the one used to calculate surface interval credit. Simple enough. Other faster compartments are certainly used in calculating ndl's.

 

[Snoopy]

Thanks for the thoughts & the info provided here. It will be some hard background reading here for me.

POP goes that old sea doogie Snoopy like a soda can. perhaps my competitor at work like to see that happening....

I will still stick to my Aladin Pro DC when diving - it uses the Buhlmann algo. So far so good. :mean:

O-ring once bubbled...
We can't go off letting Snoopy use neo-Haldanian crap now, can we? He will be doing all his stops at 10' and calculating his deco stops for the maximum overpressure gradients...he'll look like a can of soda..