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66 PHYSICALSECURITYSome airborne particles are liquid droplets oraerosols.
Those produced by industrial processes may be highly
corrosive. A more common and particularly perni-
cious aerosol is grease particles from cooking, per-
haps in an employee lunchroom; the resulting residue
may be less obvious than dust and cling more tenaci-
ously.
Smoke consists of gases, particulates, and possibly
aerosols resulting fromcombustion(rapid oxidation, usu-
ally accompanied by glow or flame) orpyrolysis(heat-
induced physiochemical transformation of material, often
prior to combustion). The components of smoke, includ-
ing that from tobacco products, pose all the hazards of
dust and may be corrosive as well.
Removable storage media often leave the protection of
a controlled environment. They can suffer from contact
with solvents or other chemicals.
There is an ever-growing list of potential chemical, bi-
ological, and radiological contaminants, each posing its
own set of dangers to humans. Most are eventually in-
volved in storage or transportation mishaps. More and
more are intentionally used in a destructive fashion. Even
if humans are the only component of the computing envi-
ronment that is threatened, normal operations at a facility
must cease until any life- or health-threatening contami-
nation is removed.Water
Water is a well-known threat to most objects of human
design. Damage to paper products and the like is immedi-
ate. Mold and mildew will begin growing on certain damp
materials. Sooner or later, most metals corrode (sooner if
other substances, such as combustion by-products, are
present).
The most critical problem is in energized electrical
equipment. Water’s conductive nature can cause ashort
circuit(a current that flows outside the intended path).
When the improper route cannot handle the current, the
result is heat, which will be intense if there isarcing(a lu-
minous discharge from an electric current bridging a gap
between objects). This may melt or damage items, even
spawn an electrical fire.
Invasive water comes from two directions: rising from
below and falling from above. Either may be the result
of nature or human action. Floodwater brings two ad-
ditional threats: its force and what it carries. The force
of moving water and debris can do structural damage di-
rectly or indirectly, by eroding foundations. In some cases,
natural gas lines are broken, which feed electrical fires
started by short-circuiting. Most flood damage, however,
comes from the water’s suspended load. Whereas falling
water, say from a water sprinkler or a leaking roof, is fairly
pure and relatively easy to clean up, floodwater is almost
always muddy. Fine particles (clays) cling tenaciously,
making cleanup a nightmare. A dangerous biological com-
ponent may be present if sewage removal or treatment
systems back up or overflow or if initially safe water
is not drained promptly. Another hazard is chemicals
that may have escaped containment far upstream. When
flooding or subsequent fire has disabled HVAC systems
in the winter, ice formation has sometimes added fur-
ther complications. Freezing water wedges items apart.Obviously, recovery is further delayed by the need to first
thaw the ice.Fire
Throughout history, fire has been one of the most impor-
tant threats to human life, property, and activity when
measured in terms of frequency, potential magnitude, and
rapidity of spread. Fire presents a bundle of the previously
mentioned environmental threats. By definition, combus-
tion involves chemical and physical changes in matter, in
other words, destruction of what was. Even away from
the site of actual combustion, heat can do damage, as de-
tailed earlier. Smoke can damage objects far from the site
of combustion. More critical to humans are the irritant,
toxic, asphyxial, and carcinogenic properties of smoke; it
is the leading cause of death related to fire. With the ad-
vent of modern synthetic materials, fires can now produce
deadlier toxins. Hydrogen cyanide, for instance, is approx-
imately 25 times more toxic than carbon monoxide.
Sometimes the cure can be worse than the disease. If
water is the suppressing agent, it can wreak havoc on adja-
cent rooms or lower floors that suffered no fire damage at
all. Some modern fire suppressants decompose into dan-
gerous substances. A comprehensive tome on fire is Cote
(1997).Power Anomalies
Electrical power is to electrical equipment what oxygen
is to humans. Both the quantity and quality of electricity
supplied to equipment are important. Just as humans can
suffer, even die, from too much or too little air pressure,
electrical equipment may malfunction or be permanently
damaged when fed the wrong amount of current or volt-
age. This accounts for approximately half of computer
data loss. Just as a properly pressurized atmosphere may
carry constituents harmful to the immediate or long-term
health of people, problems can arise when the power being
supplied to a computer is itself conveying “information”
in conflict with the digital information of interest.Power Fluctuations and Interruptions
Low-voltage equipment such as telephones, modems, and
networks are susceptible to small changes in voltage. In-
tegrated circuits operate on very low currents (measured
in milliamps); they can be damaged by minute changes in
current. Power fluctuations can have a cumulative effect
on circuitry over time, termed “electronic rust.” Of the
data losses due to power fluctuations, about three fourths
of culpable events are drops in power.
The power grid, even under normal conditions, will de-
liver transients created as part of the continual balancing
act performed in distributing power. Loose connections,
wind, tree limbs, and errant drivers are among causes of
abnormalities. Both the power grid and communications
can be affected by so-called space weather. The Earth’s
magnetic field captures high-energy particles from the so-
lar wind, shielding most of the planet while focusing it
near the magnetic poles. Communications satellites pass-
ing between oppositely charged “sheets” of particles (seen
as the Aurorae Borealis and Australis) may suffer induced
currents, even arcing; one was permanently disabled in