Posted
27.08.2024
Difference between HAZOPs and PHRs
HAZOPs (Hazard Operability) studies were developed in 1960s for the detailed design stage of projects to ensure sites installed what was shown on the Piping & Instrumentation Diagrams (P&IDs) and meet the required standards and have a suitable design which ensured key process safety risks were addressed. The study involves splitting the process into nodes as individual lines on the P&ID (continuous processes) or steps in the operating sequence (batch processes). A series of guidewords are used to identify all the causes and deviations from the design intent and a team of experienced operations and technical staff consider if these deviations could escalate to a major hazardous event. If a major hazardous event can occur, then the risk requires to be assessed including key safeguards which are required to ensure the risk is prevented or mitigated.
PHRs (Process Hazard Re-validations) studies were developed in 1990s for periodic reviews of existing sites as it was found HAZOP studies would take too long for busy operations staff and they required a quicker solution for carrying out a hazard study. The PHR takes a wider view of the process and splits the process into larger nodes at a system level. They will typically then look at the major hazardous event i.e. loss of containment or explosion and look at what preventative and mitigating barriers there are in place for each of the potential events.
When to use a HAZOP or PHR?
HAZOPs are typically used for evaluating a new process or design which has never been evaluated before and which requires a more extensive risk assessment. They can also be used if making significant modifications to a process, as a part of the start-up process, for regulatory compliance or after any incidents have occurred to ensure they don’t happen again.
PHRs are typically used when there has been a small modification to an existing process or re-evaluating a process after 5 years to ensure no modifications have taken place which could cause a major hazard event. The key changes from management of change (MOC) should be used in the PHR process so all the changes are incorporated in the revalidation process. The revalidation process helps to ensure the original hazard study is current and ensures that any new risks or changes in the process environment are properly addressed.