UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
5-6.4
The net probability of not being detected by either Zone A or Zone B can be
calculated by multiplying the chances of not being detected in either A or B together as
follows:
= (1-Pd) A * (1-Pd) B
=5% * 5%
=0.25%
=0.0025.
Thus the probability of not being detected by either intrusion system A or B is 0.25%,
which is another way of saying the probability of being detected is 99.75% or nominally
99%.
5-6.5
In the above example, two solutions of meeting a requirement to meet the Pd
of 99% were analyzed. There are other options than the two discussed. The example
presented is an academic case study to demonstrate different values of Pd for and
methods of layered protection. It is based on convenient Pd factors for two common
intrusion detection technologies based (fiber optic fenceline and buried cable). For each
project, the IDS designer will have to design a solution taking into account project
requirements, available technology, site-specific information, and possible causes of
false alarms.
5-6.6
Additional IDS design guidance is provided in Tables 5-6 and 5-7.
Table 5-6. IDS Design Guidance
Issue
Recommendations
Restricted area perimeter monitoring should be
Door Status Monitoring
included at all building entrance and exit points, to
include perimeter doors, roof hatch openings, and
doors used for emergency egress.
Doors for emergency egress should include an audible
device (door screamer) on the secured side.
All door monitoring should be via balance magnetic
switches. The status switch contacts shall be closed
when the door is closed.
In large critical systems, plan an alternate path for
Redundant Path for
alarms. One method of achieving this is to route IDS
Alarms
alarms into the ACS and out to the Dispatch Center as
an alternate path to a normal primary route of having
the IDS inputs report directly to the Dispatch Centers.
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