A HAZOP is a design verification process. It should not be used as a design development
process. The HAZOP should be performed at the stage in the design process when all
preliminary engineering is complete and the basic design has been fixed. This includes complete
process design, process flow diagrams, P&ID’s, plant and equipment layout, operating
philosophy, control and instrumentation philosophy, utilities requirements, specification and
selection of major equipment items, protection systems, start up and shutdown systems.