I've been following this thread with good interest.  Are we saying that on
this particular profile that had we lost the 50/50 mix that we should
probably just follow the planned 50/50 stops but use back gas?  Then do our
planned 100% stops as scheduled?  I think this probably works if you could
just come up to 20 foot anyway.  Knowing that most people are not in the
same shape as George, the question is for the normal diver in relatively
good shape who has done similar dives without having to resort to in-water
contingency planning (i.e. has not lost a gas) and has had no trouble,
should they just follow the planned schedule substituting back gas for
50/50?  Sorry so long but that's just the way it came out.  

I think to summarize and simplify, if in descent shape and experienced in
these types of dives and you loose the deeper gas should you:
a). Substitute lost gas with previous gas (possibly back gas) and continue
with planned schedule.
b). Do to previous gas (back gas in this instance) and try and fudge a
little by adding stops (probably dangerous on deep stops)
c). Panic and surface, signal for correct gas and try and go down and hold
your nuts hoping someone comes to the rescue.
d). Something else?

The above assumes that "previous gas" is probably better than just saying
bottom mix.  Correct me if I'm wrong but I would assume that if you were
using say 35% Nitrox, 50/50 and O2 in the schedule you should use the
remaining 35% for the 50/50 stops if you lost the 50/50 gas.  Maybe on a
profile where you're necessitating more than 2 deco gases the answer
changes.

Thanks,
Art.


	-----Original Message-----
	From:	kirvine@sa*.ne* [SMTP:kirvine@sa*.ne*]
	Sent:	Monday, January 10, 2000 10:14 AM
	To:	Shimell, David (shimell)
	Cc:	Ian PINKSTONE; techdiver@aquanaut.com
	Subject:	Re: I think I understand

	Move up = shallower. You can do the 50% as if it were oxygen
timewise,
	and if you lose that you can do the backgas as if it were 50% and go
to
	the oxygen. What I am saying is do not extend the table because you
have
	the wrong gas - the upper deco steps can be screwed with
unmercifully
	without any real consiequnces, it is the deep ones that you must so
	corectly.

	I'll let you in on a little secret - you could do this dive and come
	right to 20 in quick steps  , do 20 minues on oxygen and get out
clean -
	done it, and done al ot worse and gotten away with it. These are the
	real measures you take in an emergency.

	Shimell, David (shimell) wrote:
	> 
	> George
	> 
	> Most interesting stuff...
	> 
	> >In real life, you are btter off moving up and taking the gradient
	> >offgassing as bubbles while still underwater than you are sucking
on the
	> >wrong gas and lengthening the stops,
	> 
	> Going pack to your suggested deco profile:
	> 
	> Profile 220' FOR 25
	> 16/50, 50% and O2
	> 
	> DEPTH   TIME    GAS
	> 160-120 1 MINUTE EACH ON BG
	> 110     1
	> 100     1
	> 090     1
	> 080     1
	> 070     5       50/50
	> 060     2
	> 050     3
	> 040     5
	> 030     8
	> 020     13      OXYGEN
	> 20-0    8
	> 
	> I would like to better understand what you mean by "moving up".
	> 
	> Following a failure of the 50%, are you suggesting that you
continue the deco
	> as if 50% had been available i.e. follow the schedule but on BG.
	> 
	> Or are you saying that 16% is so worthless that you would skip the
stops and
	> go straight to O2 at 20', if so what kind of ascent would you do
from 70' to
	> 20' to give your system a chance to cope with the bubbles?
	> 
	> David Shimell
	> Email: shimell@se*.co* <mailto:shimell@se*.co*>
	> Project Manager, IBM NUMA-Q, Sequent Computer Systems Limited,
	> Weybridge Business Park, Addlestone Road, Weybridge, Surrey, KT15
2UF, UK
	> registered in England and Wales under company number: 1999363,
registered
	> office as above
	> 
	> -----Original Message-----
	> From:   kirvine@sa*.ne* [SMTP:kirvine@sa*.ne*]
	> Sent:   Thursday, January 06, 2000 4:48 PM
	> To:     Ian PINKSTONE
	> Cc:     techdiver@aquanaut.com
	> Subject:        Re: I think I understand
	> 
	> Ian, these decos are so severely overstated that a loss of a gas
is
	> insignificant. I did a whole Wakulla deco on my 190 bottle right
through
	> 20 feet on a 30 minute bt at 300 and never got hit, using a
schedule for
	> switching. I kept screwing up the gas switch and not knowing it. I
only
	> found out when I got to 20 feet and my O2 was not there, and I
then saw
	> that my 120 and 70 bottle were both untouched, and that I was
about out
	> of gas on my 190 bottle. So much for deco.
	> 
	> In real life, you are btter off moving up and taking the gradient
	> offgassing as bubbles while still underwater than you are sucking
on the
	> wrong gas and lengthening the stops, and in real life if you have
	> anything approaching the deocompression time that you are
suggesting
	> here, you not only have support with extra gases available, you
have
	> buddies to share with. I just did a dive wher I shared the 70
bottle
	> with my dive partner last Sunday, and it worked fine.
	> 
	> --
	> Send mail for the `techdiver' mailing list to
`techdiver@aquanaut.com'.
	> Send subscribe/unsubscribe requests to
`techdiver-request@aquanaut.com'.

	--
	Send mail for the `techdiver' mailing list to
`techdiver@aquanaut.com'.
	Send subscribe/unsubscribe requests to
`techdiver-request@aquanaut.com'.
--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]