Hazard Analysis Methods Compared: STPA vs. HAZOP vs. FHA for Complex Systems
A structured comparison of three major hazard analysis methods finds that STPA identifies significantly more control-related hazards in complex interactive systems, while HAZOP remains superior for well-understood process systems. Neither dominates across all system classes.
STPA vs. HAZOP vs. FHA: When to Use Which
The proliferation of hazard analysis methods has created decision paralysis for some programs. This comparison provides empirical data on when each method performs best.
STPA (System-Theoretic Process Analysis): Strongest performance on systems where hazards arise from control interactions between components rather than component failures. Found 34% more control-related hazards than HAZOP in the study's autonomous system case studies.
HAZOP (Hazard and Operability Study): Strongest performance on well-understood process systems (chemical plants, industrial automation) where failure modes are well-characterized. Process-following approach produces very thorough results for systems that fit its assumptions.
FHA (Functional Hazard Assessment): Most efficient for initial scoping at the system level. Produces FDAL/ASIL assignments quickly, making it the right tool for early program decisions even if it doesn't capture interaction hazards.
Practical recommendation: Use FHA for early-program hazard classification. Follow with STPA for systems where control interactions are a significant hazard driver. Use HAZOP for process-intensive subsystems where it's the industry norm. Don't try to use a single method for the entire system.