(54bs) Unrevealed Failures of Safeguards Used in Process Hazard Analysis  - Improving and Understanding Functionality

Safeguards credited in Process Hazard Analysis (PHA) can have enhanced performance, when their potential for unrevealed failures are reviewed revealed in the PHA sessions. The safeguard performance improvements can include additional monitoring of its “state of operability” prior to when called upon to function and by the predicted demand frequency for appropriate maintenance intervals.

Unrevealed failures of safeguards are a common “root cause” in process safety incident investigations. They are defined as systems or equipment that can remain in a failed state of operation without the knowledge of operations. The distinction between “double jeopardy” and unrevealed failures are presented with examples and definitions to improve understanding of these issues when conducting PHAs.

Safeguards that may have unrevealed failures include switches to trip a piece of equipment’s operation or alarm, check valves, and basic process control systems. The severity of consequences (hazards) associated with credited safeguards are factors for determining the interval of maintenance and the appropriate use of tools (additional devices). Additionally, the demand to function and equipment age (run to failure) issues should be included in the analysis of unrevealed failures.

The identification of these types of deficiencies (safeguards with unrevealed failures) in PHAs and operation systems can improve overall system performance in reducing and/or controlling process safety risks.