Once FSA3 is complete, hazards are then introduced to the facility and the life cycle then moves into the Operation and Maintenance phase of the life cycle.

During this phase the objective is to ensure that the required SIL of each safety instrumented function  is operated, tested and maintained to the design parameters set out in the SRS.



As part of the SRS development and SIF design a number of design principles and relationships will have documented, for example; proof test interval, MTTR (mean time to repair), failure rate on demand, maintenance overrides and startup, shut down conditions.

These design criteria need to be periodically tested to ensure al functions work as designed. The test frequency is set by the PFDave calculation completed as part of the SIF design. If for any reason the SIF is not meeting its design criteria then it may not be giving the correct risk reduction and therefore the SIS may not be meeting the corporate risk criteria set out in the Functional Safety Management System.



Using well developed maintenance proof test you are able to test not only that the process trip point functions but all relevant parts of the SRS and SIF design, these include;

  • Proof test is written for process end to process end (end to end testing)
  • Negative testing is included power failure, air failure, over and under range failure to safe state
  • SIF testing does not create a hazard while testing
  • Alarms function with correct wording
  • Overrides function correctly (as per the design)
  • Process safety time is measured against actual SIF test time

The maintenance proof tests are there to highlight any undetected failures and therefore should be audited along with number of operational demands, causes for the demands on the SIS and any causes of false trips on the SIS.



All Fulcran Engineers and Technicians are from an operational background that enables us to develop Operational and Maintenance documentation that is fit for purpose and can be utilised in the field.

We also assist our clients in setting up audit plans to ensure they understand what they are looking for and what needs to happen if a failure happens (validation procedures before the SIF or SIS is put back into service).

Our technicians can be used to either complete the maintenance proof test or we can become part of the maintenance testing team, giving on the job training until the clients technicians are competent in leading the maintenance proof tests.


For more information on Functional Safety Services please use the “Contact Us” page or give us a call.