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Ronald writes:
>>
Chuck and other List participants:
"Common failure mode", as applied to scuba equipment, is an issue that
concerns me greatly. I've often wondered whether, for example, a tech
diver ought to utilize different (albeit both superior) regulators on
his/her manifolded doubles--say, a Scubapro Mk 20/G250 on one post and a
Poseidon Odin on the other, since they appear to have distinct failure
modes--as a hedge against the common failure mode of "redundant"
regulators.
As a second example, should a tech diver carry backup lights that are
both identical?
All replies shoud be addressed to the List. Thanks in advance for your
input.
Ronald
P.S. For the record, in my five years of extended range diving in the
Great Lakes, I have personal knowledge of only one occasion when both of a
diver's regulators failed. Both of the diver's regulators were Poseidon
Odin first stages with Scubapro D400 second stages. The diver was using
air in his manifolded HP 100's. Water temperature was near 40 F.
Depth was approximately 200 ffw. The diver switched to his backup second
stage reg when his primary began free-flowing. The backup began
free-flowing almost immediately. Common failure mode?
P.P.S. My apologies if this topic has been discussed before; I've been
observing the List for only one year. And I was unable to find any
reference to this topic in the Archives.
<<
=================================
Ronald,
No apologies necessary! It is sometimes hard to find things in the
archives if the subject line of the post is not very specific.
I don't think that two "proven reliable" lights of the same design is any
problem
where failure to burn is concerned. The environmental factors that effect
one pretty much effects them all the same way (temperature extremes,
vibration, pressure). More important would be the need to comply with the
intended application.
I have had so few problems with regulators that my knowledge of "distinct
failure modes" is all gleaned from the experiences of others, and it is thin.
I don't think it is a "bad" idea to run two different designs and many divers
will
put a diaphragm on one post and a piston on the other (as you have indicated
above). Given proper maintenance, however, it may be a moot point in a
typical
environment.
In an environment of heavy suspended material such as a search and
recovery
diver or a commercial diver working in a harbor might encounter or in cold
water
this practice might be more reasonably justified.
This failure mode thing and back up systems in general interests me too and
I could write volumes on the subject but, regrettably, I just don't have time
now.
I began to think about it in regard to rebreather systems where dependency
on
intricate hardware was high and that hardware was likely to be very similar in
design, condition, and exposure. In open circuit applications, however, it
is
more difficult to achieve this degree of consistency (even if you try) that,
in a
sense, puts all your eggs in one basket. Also, since open circuit equipment
is
primarily mechanical with little use of chemistry or electronics it is less
effected
by environmental factors that concern the rebreather designer and user.
I came to realize, however, that there are different kinds of
"environments"
important to diving and also that the creation of backup systems of any kind
involved intangibles that were just as much components or elements of a
working
system as are the electronics of a rebreather. These, it seems to turn out,
are
just as subject to the nuances of redundancy and back up systems as the
delicate and sensitive components of a rebreather but more from the standpoint
of software than hardware. The inclusion of the human factor makes for some
interesting academic, though very applicable, considerations that are absent
in
the purely hardware oriented rebreather concerns.
If I ever get time I would like to post something on this because I think
it
could generate some interesting debate and insights. Maybe soon.
Chuck Boone
--
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