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i) Safety function will not work at all
Counter-measures:
•
Log forces no matter how temporary, with system to ensure removed
•
Only allow self-revealing forces
•
Modify test procedures – e.g. to inspect communication blocks, or test
SIFs in appropriate order (test the SIF that is required to be forced last)
•
Design for testing and operation, avoiding the need for forces. E.g.
prohibiting maintenance override may necessitate a force to re-start the
plant.
•
Competence, auditing, awareness and commissioning supervision of
logic solver vendor.
Neil Wakeling, August 2014