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PHYSICALTHREATS TOINTEGRITY ANDAVAILABILITY OFRESOURCES 65Table 1Temperature Thresholds for Damage to Computing ResourcesSUSTAINED AMBIENT TEMPERATURE
COMPONENT OR MEDIUM AT WHICH DAMAGE MAY BEGINFlexible disks, magnetic tapes, etc. 38 ◦C (100◦F)
Optical media 49 ◦C (120◦F)
Hard-disk media 66 ◦C (150◦F)
Computer equipment 79 ◦C (175◦F)
Thermoplastic insulation on wires carrying 125 ◦C (257◦F)
hazardous voltage
Paper products 177 ◦C (350◦F)Source: Data taken from National Fire Protection Association (1999).Temperature and Humidity
The internal temperature of equipment can be signif-
icantly higher than that of the room air. Although
increasing densities have brought decreasing currents at
the integrated circuit level, dissipation of heat is still a
major concern. If a cooling system fails, a vent is blocked,
or moving parts create abnormal friction, temperature
levels can rise rapidly.
Excessively high temperatures can decrease perfor-
mance or even cause permanent damage to computer
equipment and media. The severity of the damage in-
creases with temperature and exposure time, and its onset
depends on the type of resource, as detailed in Table 1.
Media may be reconditioned to recover data, but
the success rate drops rapidly above these thresholds.
Magnetism—the essence of much data storage—can be
affected by temperatures higher than those listed; there-
fore, damage to magnetic media occurs first in the carrier
and binding materials. On the other hand, silicon—the
foundation of current integrated circuitry—will lose its
semiconductor properties at significantly lower tempera-
tures than what it takes to melt the solder that connects a
chip to the rest of the computer.
To put these temperatures in perspective, some heat-
activated fire suppression systems are triggered by ambi-
ent temperatures (at the sensor) as high as 71◦C (160◦F).
Even in temperate climates, the passenger compartment
of a sealed automobile baking in sunlight can reach tem-
peratures in excess of 60◦C (140◦F). If media or a mobile
computer is directly in sunlight and absorbing radiant en-
ergy, the heating is more rapid and pronounced, especially
if the encasing material is a dark color, which, in the shade,
would help radiate heat. (Direct sunlight is bad for optical
media even at safe temperatures.)
Although excessive heat is the more common culprit,
computing equipment also has a minimum temperature
for operation. Frigid temperatures can permanently dam-
age mobile components (e.g., the rechargeable battery
of a laptop computer), even when (in fact,especially
when) they are not in use. Plastics can also become
more brittle and subject to cracking with little or no
impact.
High humidity threatens resources in different ways.
For electrical equipment, the most common problem is
the long-term corrosive effect. If condensation forms,
however, it brings the dangers posed by water (detailedlater). Magnetic media deteriorate byhydrolysis,in which
polymers “consume” water; the binder ceases to bind mag-
netic particles to the carrier and sheds a sticky material
(which is particularly bad for tapes). Obviously, the rate
of decay increases with humidity (and, as for any chemi-
cal process, temperature). Formation of mold and mildew
can damage paper-based records, furniture, and so on.
It can also obstruct reading from optical media. A big-
ger concern for optical media is corrosion of the metallic
reflective layer. In tropical regions, there are even docu-
mented cases of fungi burrowing in CDs and corrupting
data; high humidity promotes the fungal growth.
On the other hand, very low humidity may change the
shape of some materials, thereby affecting performance.
A more serious concern is that static electricity is more
likely to build up in a dry atmosphere.Foreign Particles
Foreign particles, in the broad sense intended here, range
from insects down to molecules that are not native to
the atmosphere. The most prevalent threat is dust. Even
fibers from fabric and paper are abrasive and slightly con-
ductive. Worse are finer, granular dirt particles. Manufac-
turing by-products, especially metal particles with jagged
shapes, are worse yet. A residue of dust can interfere
with the process of reading from media. Dirty magnetic
tape can actually stick and break. Rotating media can be
ground repeatedly by a single particle; a head crash is a
possible outcome. A massive influx of dust (such as oc-
curred near the World Trade Center) or volcanic ash can
overwhelm the air-filtering capability ofHVAC(heating,
ventilation, and air-conditioning) systems.
Dust surges that originate within a facility due to con-
struction or maintenance work are not only more likely
than nearby catastrophes, they can also be more difficult
to deal with because there is no air filter between the
source and the endangered equipment. A common prob-
lem occurs when the panels of a suspended ceiling are
lifted and particles rain down.
Keyboards are convenient input devices—for dust and
worse. The temptation to eat or drink while typing only
grows as people increasingly multitask. Food crumbs are
stickier and more difficult to remove than ordinary dust.
Carbonated drinks are not only sticky but also far more
corrosive than water. In industrial contexts, other hand-
borne substances may also enter.