Maintenance of Safety Control Systems

Procedures should be available for maintenance activities including:

  • Maintenance instructions;
  • Control of spares (segregation of faulty or non-conforming parts, identification to prevent interchange of similar parts etc.);
  • Competence of maintenance personnel;
  • Operating restriction during maintenance;
  • Control of software back-ups and memory media (E/EPROMS, floppy disks, files on hard disks on portable PCs etc.);
  • Post maintenance reinstatement and proof testing.

For systems where a high diagnostic coverage is claimed, for example high integrity high systems, the probability of failure (expressed as failure rate) is critically dependant upon the mean time to repair the faults revealed. For such systems, the repair performance should monitored and reviewed against the design criteria.