At 08:10 PM 7/25/2007, Sean Donelan wrote:
>Sometimes you need to revisit the rules. For example,
for folks
>thought having automatic water sprinklers in data
centers was a bad
>thing. Slowly folks have started to rethink it, and now
automatic
>sprinklers are
>found in more data centers. I don't have hard data, but
my experience
>is there have been fewer outages from accidental
sprinkler discharges
>than from accidental EPO activations.
There was an interesting study conducted by the US Air Force
about
fires and other failure modes in computing facilities
protected with
Halon/FM200/FE227 vs. dry pipe preaction. I know I saved the
PDF, but
I can't seem to find it at the moment. If my memory is
correct, it
boiled down to the fact that there had only been two fire
incidents
at all US Air Force installations and both were due to
(surprise,
surprise) human factors. One was a stray incendiary munition
which
breached the datacenter and other was due to a Jet A fuel
spill and
fire - which is odd because it is hard to ignite kero,
diesel, jet A
without atomization. The point of the study was that there
was zero
damage over a 30 year period from water based fire
protection systems
and I suspect it was pretty handy to have sprinklers when
both
datacenter fires happened. The munition breach of the
physical
structure would have rendered any gas based fire suppression
system
ineffective.
In theory, I'm not a big fan of EPOs due to the "Is
this the button
to exit/open the door?" problem. One of our redundant
150KVA UPS
units caught fire a couple years ago, the input breaker
became the
EPO since the on-board front panel EPO was completely
ineffective
(and it still would have been ineffective had it been
connected to an
external EPO button.) That incident prompted a design change
in all
of our new datacenter power systems since and all existing
systems
were also updated. Now all UPS units have separate input and
bypass
breakers and feeds. Previously we used a single feed, but
you can't
isolate a burning UPS without dropping your attached load
when they
share a single breaker and are tied together inside the unit
where
the fire is happening. Having discrete A & B power
systems is also a
very good thing!
Many years ago when we were much, much smaller, the EPO was
wired to
a special EPO circuit breaker on the main panel which fed
the
subpanel for the datacenter room. A short on that breaker
was like
pressing the "test" switch on a GFCI breaker. Do
most people who do
have functional (as opposed to decorative) EPO buttons have
them
connected to the building/suite mains disconnect? or to the
output of
your UPS units? to a special EPO panel which trips the EPO
cutoffs on
other units?
-Robert
Tellurian Networks - Global Hosting Solutions Since 1995
http://www.tellurian.com
| 888-TELLURIAN | 973-300-9211
"Well done is better than well said." - Benjamin
Franklin
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donelan.com>
Subject: History of the EPO (Emergency Power Off)
>> The interesting thing about the EPO and data
centers is it wasn't
orginally for life-safety, but came out of a recommendation
by IBM
to the NFPA for property protection.<<
Fwiw, the EPO on IBM's mainframes back in those days, had
to be -pulled- and had a mechanical 'latch' that kept it
from being
pushed back in. Took both hands to reset it.
--Michael