M Values and Gradient Factors - Explained

[Garf]

Originally Posted by John Touhig

did you mean 7.77 bar....


and you run DECO on the fly... tut tut tut

no no no no.

I run the deco, Howard puts up the Bag. Gareth is told to fold his arms so he cant touch anything on the ascent and has to ask permission to dump gas from his wing.

And now you know why

[GLOC]

Oh Bollox.....Been a bad dealing with f*ing Tech Support at an ISP who I pay to do my business. W@nkers!!

[Garf]

Paging Mr Payne. Will a Mr Payne please attend this thread.

[wilbo]

Garf - there is no need. Gareth is doing just fine all on his own..


Which chimp is Gareth?

[Adrian Kelland]

Originally Posted by John Touhig

did you mean 7.77 bar....


and you run DECO on the fly... tut tut tut

I did wonder, but then as I am completely ignorant of how they (DIR) do deco, I thought maybe there was somekind of built in frig figure.

[Howard Payne]

We're all going to diiiiiiiiiiiiiieeeeeeee
Are we allowed to chuck turds at each other now - I love that bit!

[dave archer]

Garf, interesting post.

A few questions spring to mind:

1) Why do all common GFs total 100, e.g. 10/90, 20/80... Is there a reason why people don't tend to choose pairs which don't total 100, such as a more conservative GF of 10/80?

2a) If you breathe 100% O2 to deco at 6m and upwards, does this mean you are at 100% of the M value? Or greater? As you have no N2 in your breathing gas.

2b) Is the bubble formation point purely driven by difference between ambient N2 pressure in breathing gas and tissue N2 pressure? I understood there was also some linkage with ambient total pressure, otherwise switching to a rich or 100% O2 mix would be like ascending upwards rapidly, and 100% O2 would never be safe... somewhat confused about this bit

Cheers,
Dave.

[neilh]

Originally Posted by GLOC

67.7msw is 5.77 bar, does that make a difference to what you were looking at?

A bit, but ignoring whether you add or subtract one ( ) the literature I've looked at so far talks about 1msw = 0.1 bar - which is the amount of pressure exerted.

My confusion is over whether the M-Value you get out of the equation is an absolute value that you compare to the ppN2 in the tissues or a value relative to sea level which should have 1 bar added (or removed ) before comparing the the ppN2

[neilh]

Originally Posted by dave archer

1) Why do all common GFs total 100, e.g. 10/90, 20/80... Is there a reason why people don't tend to choose pairs which don't total 100, such as a more conservative GF of 10/80?

Some people do: DOTF roughly equates to 30/85 I think.

Originally Posted by dave archer

2a) If you breathe 100% O2 to deco at 6m and upwards, does this mean you are at 100% of the M value? Or greater? As you have no N2 in your breathing gas.

The M-Value controls how far you can ascend based on the ppN2 in the tissues. Breathing 100% O2 just means that you won't be adding an N2 for the rest of the ascent. You can still adjust how close to the M-Values you are by adjusting the ascent.

Originally Posted by dave archer

2b) Is the bubble formation point purely driven by difference between ambient N2 pressure in breathing gas and tissue N2 pressure? I understood there was also some linkage with ambient total pressure, otherwise switching to a rich or 100% O2 mix would be like ascending upwards rapidly, and 100% O2 would never be safe... somewhat confused about this bit

My understanding is that bubble formation is related to the the ppN2 in the tissues and the ambient pressure (i.e. your depth and not the breathing gas). The gas you breathe is another way of increasing the rate of off gasing by increasing the difference between the ppN2 of the inspired gas and the ppN2 in the tissues.

[GLOC]

Originally Posted by neilh

A bit, but ignoring whether you add or subtract one ( ) the literature I've looked at so far talks about 1msw = 0.1 bar - which is the amount of pressure exerted.

My confusion is over whether the M-Value you get out of the equation is an absolute value that you compare to the ppN2 in the tissues or a value relative to sea level which should have 1 bar added (or removed ) before comparing the the ppN2

Um, Urr, Um....Don't know, and won't comment following my supreme tw*tness above. Speak to Gene or Mark Powell