Dive Computer Simulator Query

[rdbark]

I've just purchased a Mares M1 and have been playing with the dive simulator mode.

I tried running a simulation down to 30m and back. Staying at 30m until a couple of minutes from my deco stop. Then ascending slowly until at around 10m or less, staying within a few mintues of deco at each level. When I reached 10m or so the time to deco went back to 99 mins.

The deco timer didn't reduce at that depth although I waited for at least 20 mins to see what would happen. I then continued up making a deco stop for 3 mins at 3-5m.

This has raised a couple of questions I'd like Dr Deco to help me with :-

1) Why did my time to deco not continue reducing after I'd passed the 10m mark ?

2) On my PADI dive table (not multi level) I noticed that the first entry is 10m. I also appreciate that this where first bar of additional pressure comes in. What I don't understand is can you stay in less than 10m of water indefinitly (assuming you have the air of course) without fear of decompression ?

Rich.

 

[dsgobie]

Anyone know the theory the Mares M1 uses?? RGBM?

Aside from that, I believe three things might have happened.

1. Depending on the theory your computer uses, and the exact amount of time spent at different depths on your way up, your computer may have counted these as "deep stops". If that is the case, it could have greatly increase the amount of no-stop dive time in the shallower, and/or repetitive dives for the day. COMPUTER THEORY MODEL DEPENDING.

2. You locked your computer out somehow and that is what you computer displays when that happens. Some computers do not handle decompression well, while others may make their best "guess" at what just happened, and what you need to do to fix/help the situation.

3. 99 is what your computer displays when you have not reached it's scale of no-stop time limits. Meaning, once you been there long enough, it will start counting down from 99, 98, 97 etc. Read through your owners manual a bit and it should have some more clues for you and us to go off of.


FEEDBACK???

 

[dsgobie]

rdbark once bubbled...
What I don't understand is can you stay in less than 10m of water indefinitly (assuming you have the air of course) without fear of decompression ?

Rich.

You have O2 exposure limits before that would happen. 150 minutes on air.

 

[Dr Deco]

Dear rdbark:

Simulation

It is not crystal clear to me from your description as to how this simulated dive is progressing. What it sounds like is that you are gradually loading you slow “compartments” so that considerable nitrogen has accumulated by the time you are shallow.

This was a problem with the slow, linear ascents recommended by Paul Bert, an early French barophysiologist. The divers would get DCS if the dive way deep enough. Haldane corrected this by suggesting that the diver should more shallow at a faster rate and thus forestall in further nitrogen uptake.

10-Meter Depth Limit

This depth was chosen by Haldane as the first point where one could acquire “the bends.” Subsequent research has indicated that the depth is much shallower. It is actually somewhere around 20 FSW.

Dr Deco :doctor:

 

[BEM]

I believe that Mares uses the Modified Haldanian Algorithm (9 tissue compartment)...

 

[rdbark]

Cheers for the information guys. In terms of feedback :-

dsgobie - 1. I'd have to look into this. 2. Don't think so it shows STOP when it's locked out after missing deco stop. 3. Possible, I'll try staying at the shallower depth for longer and see what happens. Also thanks on the 150 mins explanation.

Computer does use the modified Haldane probably also 9 tissue compartments. I'd need to check to be sure.

Dr Deco. - I'd have to admit I don't really understand the "compartments" stuff. I'm going to read around more on here and see if I can get a clearer understanding. Any online resource you can recommend that would provide me with more information would be appreciated.

Forgive my ignorance but what does FSW mean. I've seen this before but can't remember what it stands for.

Finally point, I find the manual supplied with the M1 pretty crap. I've been online and downloaded more info from Mares website but it doesn't actually give any example scenarios that I think would be a big help. Maybe I'm expecting too much, appreciate that these things are supposed to be used in conjunction with divers own knowledge.

Oh, and I'm in the UK hence the time lag

Rich.

 

[dsgobie]

rdbark once bubbled...


Forgive my ignorance but what does FSW mean. I've seen this before but can't remember what it stands for.

FSW= Feet Salt Water...

 

[rdbark]

Ahhhhhh.....

 

[rdbark]

Found this for anyone intersted in reading more about Deco, compartments, tissue and all that stuff..........

http://www.harcourt-international.com/e-books/pdf/317.pdf

 

[Dr Deco]

Dear rdbark:

Tissues

When Haldane first conceived of his method for decompression, the procedure was to slowly bringing divers to the surface in a linear ascent rate. This lead to DCS as the depths passed 100 feet and the bottom times lengthened. Haldane noted that nitrogen was taken in quickly in his goats. To translate this is a realistic decompression procedure, however, he assumed that some gas was absorbed quickly and some gas was taken on more slowly. He attributed this to varying amounts of blood flowing to the organs of the body. This lead to the idea of ”half time tissues” in decompression physiology. By this, Haldane meant that muscle quickly loads nitrogen but fat did so slowly. By the 1970s or so, the idea of individual tissues gave way to "half time compartments.” These compartments could be small, individual regions scattered around the body, not simply a whole organ. [Professor Buhlmann did retain the idea of half time tissues as true organs, however.]

Compartments

When barophysiologists speak of compartments today, they think that these can be regions with different perfusion rates and differing in the amount of lipid (fat) that they contain.

In the model that I have developed, compartments do not vary in lipid content but are determined solely by blood flow (for joint pain DCS anyway). This blood flow, and thus the halftime, can change with activity in a predictable fashion. This is not the model used to develop tables today, however. It is essentially a one-tissue model.

Dr Deco :doctor: