Integrated PHA & LOPA Review Guideline to improve the SIL Classification Process

The integration of layer of protection analysis (LOPA) with process hazard analysis (PHA) conducted using the hazard and operability (HAZOP) methodology has become the best approach to Functional Safety Management. Until a few years ago, Safety Integrity Level (SIL) assessment study in the form of integrated LOPA was not always conducted in quick succession to the PHA study, or with the same team, during the Front-End Engineering Design (FEED) phase of a typical LNG or petrochemical facility. This has often led to incorrect allocation of required risk reduction by a Safety Instrumented Function (SIF).

Experience has confirmed that having the same team participating in integrated PHA and LOPA reviews has improved the effectiveness of both studies by:

• Eliminating analysis of the same hazard-consequence scenarios twice,
• Bringing consistency with risk assessed previously in HAZOP reviews and later SIL level classification (or assignment),
• Having fewer optimized preventive or mitigative actions compared to performing only a HAZOP, and
• Faster support of control systems engineering with comprehensive preparation of the Safety Requirement Specifications (SRS).

This presentation details the concept/guidelines of integrating LOPA with PHA using the HAZOP methodology. This approach has been internally adopted in Bechtel Oil, Gas & Chemicals, Inc. across several projects, achieving efficient and consistent results.