Robert, I once worked for a company where we convinced ourselves and two
safety agencies that we could live with a reduced fire enclosure because the
fault testing showed that a fire could not start, and even if it did, it
would not propagate internally. We actually placed a torch to the internal
plastic components to demonstrate that they would self-extinguish. Guess
what? We had a fire in the equipment and all of those unburnable parts
burned. Luckily the enclosure held, but it was obvious that we were deluding
ourselves about what can really happen in equipment. I am now much more
conservative when it comes to fire enclosure design. I have learned that you
cannot foresee every incident and it is what you don't know that will hurt
you. In your case, I recommend a baffle construction that allows for larger
openings.
Richard Woods
----------
From: Robert Legg [SMTP:[email protected]]
Sent: Monday, November 06, 2000 8:30 AM
To: IEEE EMC-PSTC Forum
Cc: athome Legg
Subject: Hot Flaming Oil/ applicability in 60950
Group,
The ventilation hole pattern on the bottom of Telecom Rack
assemblies seems
to have been adopted from older standards. This was to address the
safety
of assemblies that might use less-than-94V-0 flammability-rated
materials,
including unfilled thermoplastics, resins, insulating oils,
varnishes and
other potential fuels.
These are materials that are avoidable at the present time, without
serious
cost implications.
The ventilation pattern permitted by the requirement is highly
restrictive
in its effects on ventilation, limiting the power density that is
achievable without the use of unreliable air movers.
Is it possible to establish safe practice, in dedicated rack assy's,
when
using more practical ventilation patterns? This could perhaps be
achieved
by reporting oxygen index limits of the components and materials
enclosed.
If you can't set it on fire with a flame thrower, then obviously it
doesn't
pose that risk to its surroundings.
Rob Legg
Tectrol Inc
[email protected]
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