Publisher Summary The bulk of process hazard analyses are hazard and operability (HAZOP), What-If, or preliminary hazard analysis (PHA) review. Generally, in the upstream sector 60%–80% of the safety reviews are PHA or What-If reviews, while in the downstream sector 60%–80% are HAZOP reviews. Security vulnerability analysis (SVAs) is applicable to all types of facilities. PHA, HAZOP, What-If, and SVA reviews are generally organized and conducted in a similar fashion. The HAZOP review is more detailed and structured, while the PHA and What-If approach, which is also applied in SVAs, is typically broader and free flowing. It has been found that the PHA or What-If style of analysis is generally a convenient method to use for a “simple” facility when conducting a process hazard review. For simple facilities, the detailed HAZOP approach has been found to be tedious and just as productive as a PHA or What-If method. The PHA and What-If approach stimulates generation of new ideas and discussion to cover issues associated with the items under review as well as addressing generic issues. The specific HAZOP review is not necessary when the process is simple and well understood by the reviewing team. It is recommended, in case of a doubt, to choose the HAZOP method over the PHA or What-If method. The PHA and What-If approach rely on the team leader to ferret out the real hazards associated with the process. The systematic HAZOP approach will examine each portion of the system to determine hazardous conditions.