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Keir Vaughan Taylor writes:
> 
> The premise is that all dive tables have a certain bend
> percentage, e.g. American Navy tables at 5%

Where did you find this figure? 

> This implies that if you dive to the limit of a certain table
> that you have a certain probability of getting bent. Presumably
> with American Navy that is 1 chance in twenty.

To the best of my knowledge, this is inaccurate, for two reasons.
(I am assuming you are talking about the no-stop limits of the tables.)
First, different depth schedules have very different characteristics.
Second, practical use studies have shown the risk to be much lower
than 1/20. 

>  Whatever the
> probability, a dive is seen to involve the act of throwing a die to
> see if you get bent.

For more on the idea of how to model the risk of DCI during diving,
see the recent papers by the Weathersby, Survanshi, Parker, et al.
These folks at the DCIEM have some pretty interesting new models of
DCI risk which are non-deterministic, and which have a plausible risk
model.  

Risk is not simply an isolated die throw, especially when you consider
repetitive and/or multi-level diving.  Surely you'll agree that there
is "residual risk" from previous dives when you perform a repetitive dive?

> However.. the bend percentage is across a population not across
> an individual. It means, that out of 100 Navy divers on the limits
> of their tables 5 will show bends symtoms. If this same population used
> more conservative tables then there would be a zero bend percentage
> no matter how many times they dived.

As others have pointed out, it is not the tables that cause DCI, it is
the diving and the diver.  No matter what table you use, you have a
nonzero chance of incurring DCI.

For more on this, keep an eye out for the next issue of AquaCorps.
There will be two articles about the new US Navy tables coming out
this year, one by the NMRI about their new model, and another by some
random crank :) describing the relative estimated risks of the US
Navy, Royal Navy, and DCIEM tables.

Cheers,

David Story                        NAUI AI Z9588, PADI DM 43922, EMT
story@be*.wp*.sg*.co*		  Every dive is a decompression dive.

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