P1: JDV
Michael WL040/Bidgolio-Vol I WL040-Sample.cls June 19, 2003 16:10 Char Count= 0
PREVENTIVEMEASURES 73International Commission on Non-Ionizing Radiation
Protection (1998).
Depending on the overall security architecture, the crit-
icality of the facility, and the anticipated threats, it may
be advisable to implement any or all of the following:- stationed or roving security guards;
- surveillance cameras, monitored in real time and
recorded on videotape; - motion detectors;
- silent alarms (of the type used in banks); and
- barriers that prevent unauthorized vehicles from ap-
proaching the facility.
Fire Preparedness
For the survival of people and inanimate objects, the most
critical preparations are those regarding fire.Fire Detection
Automatic fire detectors should be placed on the ceilings
of rooms as well as in hidden spaces (e.g., below raised
floors and above suspended ceilings). The number and
positioning of detectors should take into account the lo-
cation of critical items, the location of potential ignition
sources, and the type of detector. Fire detectors are based
on several technologies:1.Fixed-temperature heat detectorsare triggered at a spe-
cific temperature. Subtypes are
(a)fusible—metal with a low melting temperature;
(b)line type—insulation melts, completing a circuit;
and
(c)bimetallic type—bonding of two metals with un-
equal thermal expansion coefficients, bends when
heated (the principle in metal-coil thermometers),
completing a circuit (until cooled again).
2.Rate-compensation detectorstrigger at a lower temper-
ature if the temperature rise is faster.
3.Rate-of-rise detectorsreact to a rapid temperature rise,
typically 7–8◦C (12–15◦F) per minute.
4.Electronic spot type thermal detectorsuse electronic cir-
cuitry to respond to a temperature rise.
5.Flame detectors“see” radiant energy. They are good in
high-hazard areas. Subtypes are
(a)infrared—can be fooled by sunlight, but less af-
fected by smoke than ultraviolet detectors; and
(b)ultraviolet—detects radiation in the 1850–2450
angstrom range (i.e., almost all fires).- Smoke detectors usually detect fires more rapidly than
heat detectors. Subtypes are
(a)ionizing—uses a small radioactive source (common
in residences); and
(b)photoelectric—detects obscuring or scattering of a
light beam.
A third type of smoke detector is theair-sampling type.
One version, thecloud chamber smoke detector,detects the
formation of droplets around particles in a high-humiditychamber. Another version, thecontinuous air-sampling
smoke detector,is particularly appropriate for computing
facilities. It can detect very low smoke concentrations and
report different alarm levels.
For high-hazard areas, there are also automatic devices
for detecting the presence of combustible vapors or ab-
normal operating conditions likely to produce fire; said
another way, they sound an alarmbeforea fire starts.
Some fire detectors, especially the fusible type, are in-
tegrated into an automatic fire suppression system. This
means that the first alarm could be the actual release of
an extinguishing agent. Because an event triggering a fire
may also disrupt the electrical supply, fire detectors must
be able to function during a power outage. Many fire
detectors are powered by small batteries, which should
be replaced on a regular schedule. Some components of
detectors, such as the radioisotope in an ionizing smoke
detector, have a finite life span; the viability of such a de-
tector cannot be determined by pushing the “test” button,
the purpose of which is merely to verify the health of the
battery. Such detectors must be replaced according to the
manufacturer’s schedule.Fire Prevention and Mitigation
Better than detecting a fire is preventing it from starting.
The two things to avoid are high temperatures and low
ignition points. It is usually possible to exclude highly
flammable materials from the computing environment.
Overheating is a possibility in almost any electrical de-
vice. In some cases a cooling system has failed or has been
handicapped. In other cases, a defective component gen-
erates abnormal friction. The biggest threat comes from
short circuits; the resulting resistance may create a small
electric heater or incite arcing.
Some factors that may lead to a fire, such as short
circuits within a machine or a wall, are beyond our con-
trol. Yet many precautions can be taken to lessen the
chances of a fire. Vents should be kept unobstructed and
air filters clean. Power circuits should not be asked to
carry loads in excess of their rated capacity. Whenever
possible, wires should run below a raised floor rather than
on top of it. If wires must lie on a floor where they could
be stepped on, a sturdy protective cover must be installed.
In any case, wires should be protected from fatiguing or
fraying. See National Fire Protection Association (1999)
for fire prevention guidelines for the computing environ-
ment. As of this writing, the newest electrical code per-
taining specifically to computing equipment is from the
International Electrotechnical Commission (2001).
Many fires are actually the culmination of a protracted
process. Another preventive measure is for employees
to use their eyes, ears, noses, and brains. Damage to a
power cord can be observed if potential trouble spots are
checked. Uncharacteristic noises from a component may
be symptomatic of a malfunction. The odor of baking ther-
moplastic insulation is a sign that things are heating up.
Given that a fire may have an external or deliberate
origin, preventing the spread of fire is arguably more im-
portant than preventing its ignition. It certainly requires
greater planning and expense. The key ideas are to erect
fire-resistant barriers and to limit fuel for the fire between
the barriers.