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 3.4.1.1 Physical. Electronic intrusion detection systems are designed to
sense and report on stimuli in their areas of application. Failure to
properly determine the environmental extremes in areas where various
subsystems will be installed may lead to increased sensitivity and nuisance
alarms or degraded performance and no alarm, excessive maintenance, and
result in loss of user confidence. Temperature extremes, environmentally
generated vibration, wind, fog, humidity, conducted and radiated
electromagnetic interference, transient light sources, and lack of
consistent power availability are some of the common causes of component
performance problems. Adequate survey techniques and data analysis of the
physical environment, over time, can substantially predict these extremes
and factor them into the system design.
3.4.1.2 Operational. It is essential that how the facility works at all
hours, under varying conditions and what the user activity requires for
efficient operation, be factored into the system design.
3.4.2 Provide for Protection-in-Depth. Also known as security-in-depth or
defense-in-depth, this concept is concerned with erecting and integrating
physical and electronic countermeasures in concentric rings around the
protected asset. The objective is to build time delays into the intruder's
access to the asset and make it progressively difficult for him to reach his
target undetected and escape. Placement of electronic detection and
assessment hardware becomes critical to maximize the potential that he must
pass through a detection pattern to carry out his mission. Protection
in-depth is also concerned with providing assurances that failure of one
element or component will not detract from the total capability of the
system or any one critical area of protection. NAVFAC DM-13.01, Physical
Security, discusses the role of physical barriers in protection-in-depth and
time delay in great detail. Moreover, the Restricted Area requirements of
OPNAVINST 5530.14 (para. 0306) reflect this concept in Navy security
practice.
3.4.3 Provide for High Probability of Detection and Low Nuisance Alarm
Rates. The system design process constantly strives to make the probability
of detecting an intruder 100 percent and the potential for nuisance alarms
zero percent. Both objectives are the ideal.
3.4.3.1 Probability of Detection (Pd). The probability of an individual
sensor detecting an intruder is calculated by dividing the number of
attempts into the number of successful detections. Most commercially
available sensors indicate a Pd of 0.95. This has been based, however,
upon tests of actual intrusions into the sensor field in a laboratory
environment. Given the environmental impacts potentially available in the
real world and the presence of a knowledgeable and determined intruder, Pd
needs to be evaluated as a system performance goal rather than as a measure
of individual sensor performance. Thus, the location of the equipment to
maximize detection, the potential use of multiple sensor arrays
(redundancy), or different types operating on different stimuli (diversity)
should be considered, particularly in higher security applications. These
techniques are consistent with the protection-in-depth concept discussed
above.
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