A Hazard and Operability study (HAZOP) is a detailed hazard and operability problem identification process, carried out by an interdisciplinary team in sessions.
The objective of a HAZOP study is to:
- Identify hazards and major operability problems,
- Assess the extent of these hazards and operability problems,
- Evaluate the effectiveness of existing prevention or mitigation safeguards,
- Propose technical and organizational measures, if necessary, to demonstrate that risk is “as low as reasonably practicable” (ALARP).
Layer of Protection Analysis (LOPA) is an analytical method for identifying and evaluating the effectiveness of independent protection layers in reducing the frequency and/or consequence severity of hazardous events.
The LOPA study is a tool to assess which Safety Integrity Level (SIL) a Safety Integrated System (SIS) needs in order to meet safety requirements. Potential accident scenarios are considered, as extracted from HAZOP study, in a semi-quantitative way by using order of magnitude numbers for parameters like probabilities of events that may initiate an accident and probabilities of failures of a number of predefined, independent protection layers.
When to do a HAZOP or LOPA;
For new installations, a HAZOP and LOPA study should be carried out early in the design phase of a project, after the process design has been finalised and before detailed design.
For existing plant and processes, HAZOP and LOPA study may also be employed as part of the Management of Change (MOC) process in the assessment of process design changes and as part of a periodic systems review.
Once the requirement of the HAZOP and LOPA studies for Safety Instrumented Function (SIF) is recognized, it must be ensured that the required Safety Integrity Level (SIL) is met in accordance with the requirements of IEC 61508 / IEC 61511.
- Pipping and Instrumentation Diagrams (P&IDs) design and revision.
- HAZOP sessions and studies conducted by certified HAZOP Leader and experienced HAZOP Scribes with PHA PRO Software.
- Preparation and visualisation of LOPA studies with the Bow Tie approach (Bow Tie XP Software of CGE Risk Management Solutions).