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.