Process Hazard Analysis (PHA) is a study that should be carried out for identification of Risk associated with operation of a High Hazard Process and provide mitigating actions (aka layers of protections) to reduce the associated risk to an acceptable level (sometimes called ALARP or As Low As Reasonably Practicable).
PHA may be carried out at following different stages of life cycle of a plant i.e.
1. Conceptual Stage PHA (when only basic technology / design is known)
2. Detailed PHA (when 70%~90% design is locked and complete details are available)
3. Pre-Startup PHA
4. Baseline PHA (after successful commissioning has been carried out)
5. Cyclic PHA (once in 5 years for HHP)
6. Decommissioning or Mothball PHA
Now PHA itself consists of two Parts
1. Consequence Analysis, which is further classified into
a. Qualitative Consequence Analysis
b. Quantitative Risk Analysis (QRA)
2. Process Hazard Review or PHR (which can be done using anyone or a combination of following technique)
a. HAZOP (Hazard & Operability) Study
b. What-if Method Study
c. Checklist Method
d. FMEA (Failure Mode & Effect Analysis)
e. FTA (Fault Tree Analysis)
In addition sometimes, various other studies are carried as part of PHR, such as, Facility Siting, Human Factor (HF) analysis etc.