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74 PHYSICALSECURITYTable 2Comparison of Types of Surge ProtectorsTYPE OF SURGE PROTECTOR CHARACTERISTICSMOV (Metaloxide Varistor) Inexpensive, easy to use, but progressively
degrades from even minor surges (possibly
leading to a fiery demise)
Gas Tube Reacts quickly, can handle big surges, but may not
deactivate until an alternating circuit polarity flip
(which may mean the computer shuts down in
the meantime)
SAD (Silicon Avalanche Diode) Faster than an MOV (1 ns vs. 5 ns), but has a
limited power capacity
Reactive Circuit Also smoothes out noise but can only handle
normal-modesurges (between hot and neutral
lines) and may actually cause acommon-mode
surge (between neutral and ground lines), which
is thought to be the more dangerous type of surge
for desktop computersFor computing environments, the choice of construc-
tion materials, design, and techniques for mitigating the
spread of fire should exceed the minimum standards dic-
tated by local building codes. Because fires can spread
through unseen open spaces, including ventilation sys-
tems, acomputing areais defined to be all spaces served
by the same HVAC system as a computing room. Air ducts
within that system should have smoke dampers. The com-
puting area must be isolated in a separatefire division.
This means the walls must extend from the structural floor
to the structural ceiling of the computer area and have
aone-hour rating(resistance to an external fire for one
hour). Care should be taken to ensure that openings where
pipe and cables pass through the fire-resistant boundaries
of the separate fire division are sealed with material that
is equally fire-resistant.
Many fires affecting a computer area do not actually
originate in that area. Even if a fire does not technically
spread into a computing area, its products—heat, smoke,
andsoot(carbon deposits)—may. Consequently, the level
of fire protection beyond the computing area is still of
critical concern.Fully sprinkleredbuildings (protected by
sprinkler systems throughout) are recommended. Con-
cern should extend beyond the building if it is located
in an area with high hazards, such as chemical storage or
periodically dry vegetation. In the latter case, afire break
should be created around the building by removal of any
vegatation likely to fuel a fire.
The standards prescribed by the National Fire Protec-
tion Association (1999) for fire protection of computing
equipment set specifications for wall coverings, carpet,
and furnishings (which are relaxed in fully sprinklered
buildings). They also limit what other materials can be
present. They do not take into account that even high-
hazard areas have computers present. In interpreting
those standards, determine which dangerous materials
are absolutely essential for operations, and work to min-
imize any unnecessary hazards. Due to their potential
contribution to fire (as well as being a more likely start-
ing point for a fire), materials that could contribute to aClass Bfire (including solvents, paints, etc.) should not be
stored in a computing area except in a fireproof enclosure.
Materials that could contribute to aClass Afire, such as
paper, should be kept to the minimum necessary.
Raised floors are standard features of many computer
facilities, allowing for cables to connect equipment with-
out the need to cover cables to prevent fraying and elec-
trical shorting. The use of junction boxes below the floor
should be minimized, however. The needed equipment for
lifting the heavy removable panels to gain access to the
space between the raised floor and the structural floor
must be easy to locate, even in the event of a fire.Power Maintenance and Conditioning
The most basic necessity for the functioning of computer
resources is maintenance of power.Power conditioning
refers to smoothing out the irregularities of that power.Surge Protectors and Line Filters
Asurge protectoris designed to protect against sudden in-
creases in current. It forms a second line of defense, the
circuit breaker being the first. Neither should be counted
on to protect against a direct hit by lightning. There is
no substitute for unplugging home computers during an
electrical storm. A large building should have a separate
lightning protection system in any case. Surge protectors
are currently based on four technologies, described in
Table 2.
Metaloxide varistor (MOV), gas tube, and silicon
avalanche diode (SAD) surge protectors short out the
surge and isolate it from the protected equipment. The
reactive circuit type uses a large inductance to spread a
surge out over time. All should have lights to indicate if
they are in functioning order. MOVs and SADs are the
types preferred for computing environments because of
their reaction times. All surge protectors require a prop-
erly grounded electrical system in order to do their job.
Line filtersclean power at a finer level, removing electri-
cal noise entering through the line power. Their concern