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Anthony,
In a message dated 98-01-11 15:01:02 EST, you write:
<< Chuck Boone <chkboone@ao*.co*> writes:
> Anthony,
>
> This was apparently simply a stuck inflator valve coupled with ice in the
dump
> valves. Could have happened to any poorly maintained and/or operated
> buoyancy device. Not the fault of the bondage wings !
I didn't say it was; in fact, I said it probably made the same sound
bursting as a single would, for whatever that's worth.
** I know. The original post said that the victim would not be buying
bondage
wings again. Just making a note of the more probable fault in this post to
you.
The main point I was trying to make was about common-mode failure analysis.
A simple-minded concept of redundancy is that if something is 99% reliable,
having a redundant one gives you 99.99% reliability. This only counts if
the two are truly independent. If one blowing up takes down the other (see
the O2 tanks in the Apollo 13 SM) or if a common external factor can take
down both systems together, then your reliability drops accordingly.
** Yep! Aware of that. Good point. But, the few odd things that "can"
happen
to the second bladder don't seem to justify any serious questioning of it's
value
as a back up as advertised. Parachutes tangle now and then but we all want
one when the engines start smoking.
You said :
>>>>However, the people who advertise this stuff tell you that the other air
cell gives you redundancy in case one fails, but there's a chance the
second cell would be compromised by the first one blowing up in this type
of incident, depending on whether it blew toward or away from its mate.
There's also the chance that even intact, the second cell would extrude
through a split in the outer jacket and cause some really interesting
bouyancy issues. <<<<
** I don't picture an actual "explosion" happening. The material of the
bladder would probably stretch under pressure but it will not have much,
if any, tendency to return to it's original shape (stretchy but not elastic).
So, no pressure will be exerted on the contained gas as it expands as
happens with a balloon so that when it finally breaks somewhere the gas
will simply blurp out like a big bubble released from a bag. However,
this bladder is confined by a tough shell so that once he bladder reaches
the limit of expansion imposed by this shell pressure will begin to build
and continue till the shell tears at a seam.
As it turns out the seams (weak spots) are all on the outside and
when one splits the bladder will probably continue to expand through the
breach, reducing pressure to near ambient again, till it finally ruptures in
the manner above. There is a chance the bladder would rupture as
soon as it expands through he tear in the shell but in any case the force
would probably be outward.
When the primary bladder ruptures there may be light shock waves
and turbulence throughout the structure as the bubble escapes but the
secondary bladder will probably be held against the primary as it
collapses for the same reason people and debris are dragged down with
a sinking ship (essentially suction). Being held against the vibrating
primary bladder will probably protect it to some degree and maybe even
pull it away from the rig as the primary collapses.
I would gamble that it will work fine though the hole in the shell could
pose some problems, but the dive is over anyway and all that remains is
to leave the scene of the crime.
Does all this sound reasonable ?
> The only way I can see cold conditions causing a failed dump valve is if he
> let ice form on them on the surface and it held them shut . Since the
> report says the diver was unhurt the incident probably happened near the
start
> of the dive before the ice could melt in the water. Diver Error ! ! !
That's a secondary problem; the main problem was the runaway inflator.
Probable analysis: water inside the wings from a previous dive would have
collected in the end of the hose and in the overpressure and frozen there.
** Agreed on the analysis ! But, edging a little closer toward the Big Bang;
the main problem was the diver's ignorance of the need to insure clear dry
lines and dump valves.
I say "main" because this is the most opportune and advantageous point
for the human factor to intervene in the chain of events and alter the course
of history (this is where he could have avoided the initial problem).
Actually, it's the increased buoyancy that would kill you, not the runaway
inflator or the stuck dump valves at all. . . . . or would it be the rapid
reduction of ambient pressure ?
> The bondage wings are designed for a fast dump in any position anywhere in
the
> known universe because there is always positive pressure on the contained
gas.
....
> So, what we have here is a diver who now fears the consequences of a stuck
> inflator valve refusing to buy the only set of wings designed specifically
to
> accommodate that exact situation if used properly because he blames the
wings
> for what appears from the report to be his own failing.
That same bondage prevents oral inflation.
** Yes, I am aware of the problems with the bondage wings. These things are
definitely dangerous in the wrong hands, but then, so is any dive gear.
It's a bit specious to say these wings are designed specifically to
accomodate an obscure failure mode, especially when the first line of
defense is an inflator that doesn't freeflow, second line is a hose kink,
disconnected inflator, or tank valve closure to stop the incoming
pressure, and third is at least one deflator that works. Positive
pressure to deflate isn't going to help if there aren't any deflators in
business, and a few bits of bungee meanwhile aren't going to slow down
your interstage pressure for long enough to make a difference.
**I see runaway inflators now and then, usually from poor maintenance,
but what I meant was that they were designed for a rapid dump rate to
stay ahead of any reasonable cause of over inflation - sorry.
--
Anthony DeBoer <adb@on*.ca*>
>>
Chuck Boone
--
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