For operations where application of standards, regulations, and/or Recognized and Generally Accepted Good Engineering Practices may not be sufficient to address a particular company's risk, several options exist. For qualitative assessment of process hazards, Hazard and Operability Studies (HAZOP) and What-If reviews are two of the most common petrochemical industry methods used. Up to 80% of a company's process hazard analysis (PHA) may consist of HAZOP and What-If reviews (Nolan, Application of HAZOP and What-If Safety Reviews to the Petroleum, Petrochemical and Chemical Industries, William Andrew Publishing/Noyes, 1994, p. 1). After the PHA, Layer of Protection Analysis (LOPA) is commonly used throughout industry to evaluate the required safety integrity level for instrumented protection layers in a semiquantitative manner (Dowell, International Conference and Workshop on Risk Analysis in Process Safety, CCPS/AIChE, 1997). HAZOP, What-If, and LOPA are all straightforward methods and are relatively easy to perform. However, much like a hammer, they are not always the best or most appropriate tool for a given job. At times, more advanced methodologies such as Fault Tree Analysis, Quantitative Risk Assessment, Event Tree, Failure Mode, and Effects Analysis and Human Reliability Analysis are necessary to properly assess risk. However, these more advanced tools come with a price. They are often more expensive, time consuming, and require a higher level of expertise. The decision to use these higher level methodologies is not taken lightly and different companies use different criteria for determining when to take this next step. This article will present approaches by four companies, BASF, Celanese, The Dow Chemical Company, and Eastman Chemical Company. Each company will outline criteria used to determine when to go beyond HAZOP, What-If, and LOPA and will present examples where more advanced techniques were used. The intent of this article is to provide readers with real world examples that demonstrate the appropriate application of the right tool and to illustrate what criteria can be used to make informed decisions regarding selection of a PHA methodology. (C) 2016 American Institute of Chemical Engineers Process
