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in every consecutive phase
are directly caused by a poor preventive maintenance (
p
Increments in the maximum value of the
p
H
(
t
)
) that cannot
detect all system failures. Increments would be even more severe if we as-
sumed
q<
=0
,
9
1
, but that case is in high SIL safety-critical systems avoided at
all costs.
4
Conclusion
System restoration could possibly happen after an unscheduled maintenance
that is usually required after the system has reached non-transient safe state
(absorbing state). Unscheduled maintenance shortens the deterministic pe-
riod between two consecutive preventive maintenances. However, this fact has
no negative effect on computed probability of the hazardous state as that will
always be higher than the probability of the hazardous state in the instant of
unscheduled maintenance. This is in full accordance with the safety analysis
philosophy.
Such analysis approach has been successfully employed to assess the safety
of the electronic interlocking systems used in ŽSR operation, even though
those systems are generally more complex and span over more levels of con-
trol.
References
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fier: 10.1109/RAMS.2010.5447972, (2010)
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