Operation and maintenance teams bear a heavy responsibility to ensure that the Safety Instrumented System integrity and reliability is sustained. Decisions made long before operation begins, or outside the operating environment often impact the ability to be successful. Design choices fix physical configuration and instrumentation capabilities. Inadequate bid assessment results in procurement of equipment that does not meet the specification. Turn around schedules are extended stretching proof test intervals beyond design plan. Budget constraints don’t provide for resources to collect field failure information and complete performance analysis. Repair and replacement is deferred. All these things conspire to reduce the reliability of a SIS and increase the probability that it will fail when needed. This paper will discuss some of the significant challenges that Operations and Maintenance teams face, and recommend techniques to incorporate as good engineering practices.