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Terry McCracken writes: > > Hi Folks > Is this a realy old thread re-raising its head or have I been sleep > typeing again.... > Just one point a bit further down that I think is wrong .... : > > means that you have a ratio, say 5:1, below which you will not form > > bubbles. > > I think that the original calculated ratio was 2:1 but nowerdays it is > belived to be about 1:7. The 5:1 ratio was simply an example. In practice (and as I mention further down in my message), there are different ratios for each compartment. These are commonly expressed as "M-values", which is simply another (equivalent) way of expressing a ratio, given a fixed surface pressure. (Buehlmann's formulas differ only in that they add a term to allow surface pressure to vary.) Here are the ratios for the US Navy tables (from memory, please don't shoot me if they're slightly off): compartment N2 Pressure halftime allowed ratio 5 4.0:1 10 3.4:1 20 2.8:1 40 2.2:1 80 2.0:1 120 1.9:1 Clearly, other models use other parameters, but if you plot these, you get a curve, and most models have a very similar curve. Cheers, Dave Story@be*.wp*.sg*.co* NAUI AI Z9588, PADI DM 43922, EMT Burning sun keeps you dry. Heavy air drives you mad. Solid water stones you down. The risk makes your life deeper.
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