Delta-HAZOP (‚HAZOP Revalidation‘ or ‚HAZOP-by-Difference‘) is method of updating the HAZOP for existing (or similar plant), while ensuring the conclusions of previous HAZOP studies remain valid and are not lost. It requires a clear understanding of changes compared to the previous HAZOP, which are generally documented via MOC procedures.
The following information should be available:
- Overview of changes made since the last HAZOP (preferably as mark-up of current PIDs)
- Is MOC up to date?
- Were there any changes to an alarm or safety system?
- Did any of the changes require modification to:
- Op. Conditions outside the operating range?
- Chemistry of the process?
- Timing or sequencing of the operations?
- Maintenance procedures or staffing level?
- Does the change affect safety or the environment?
- Operator experience, Lessons learned, Root-cause analysis?
If significant changes have taken place, a new HAZOP (redo) should be done.