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On Fri, 8 Jul 1994, Richard Pyle wrote:

> 
> 
> On Fri, 8 Jul 1994, Jody Svendsen wrote:
> 
> > > Note that although I have He in my tissues as well as N2 from my gas
dive, we
> > > can ignore the He on the second dive since there isn't any in the air I
will
> > > be breathing.
> > 
> > Sorry if this sounds like a flame, but this is totally wrong.  Just 
> > because you are not breathing on a gas does not mean that it can't bend 
> > you.  There will still be helium in your body on the second dive, and 
> > it will increase your decompression requirements.  
> 
> Jody,
> 
> Could you please elaborate on this? Assuming he'd not been bent on the
> first dive, wouldn't he continue to off-gas helium throughout the 2nd dive?
> How could the helium in his body from the first dive cause problems after
> the 2nd dive? Are you thinking in terms of helium bubbles formed after
> the first dive (as per David Doolett's comment)? It's not that I doubt you,
> it's just that I'm not sure I understand your reasoning.
> 
> Aloha,
> 
> Rich
> 
Well I took entriely another approach, more empirical than hypothetical.
What I did was run a set of tables for the Trimix dive. Although the deco 
program I use , DECOM, does not emulate the Aladdin Pro I though the 
following would approximate it. I set my conservatism to 0, running a 
straight Buhlman. Then instead of using instantaneous descent to depth, I 
ongassed 1 minute @30, 1 minute @ 60, 1 minute @90 ....... till I got to 
bottom. I then completed my bottom time.
I then "ongassed" at bottom-30 for 1 minute, bottom-60 for 1 
minute....till I hit my first deco stop on the Trimix table. I then used 
the stops and deco times and followed it to end (well as close to the end 
as possible). In this instance after I finished my "ongass" (its actually 
an offgass, but DECOM takes care of the direction of gas flow based on 
pressure gradients) at 30 ft my cieling was 22 ft. At that point I invoked 
the deco function of DECOM to complete the dive. When I finished the air 
dive I had 16 more minutes on the Pro than on my body. So on the next 
dive I ran the table on my body with Surface Interval + 16 minutes 
compared to the Aladdin Pro. 
I used 120 minute SIT for my Pro Table and 136 for my body.
IN THIS INSTANCE the PRO would give you a safe second dive. I haven't run 
multiple scenarios and examined the individual compartment pressures so I 
can't even form an opinion as to whether this might be a procedure I 
would subject my body to but there's my 2 cents worth.
Not sure how many "ongasses" other programs allow, but it is no problem 
for DECOM!
TTFN
Ronnie Bell in Arlington Virginia 

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