(77b) Requirements For Improved PHA Methods: Addressing Weaknesses In HAZOP and Other Traditional PHA Methods

In order to develop better process hazard analysis (PHA) approaches, weaknesses in current approaches must first be identified and understood. Criteria can then be developed that new and improved approaches must meet.

Current PHA methods share common weaknesses such as their ability to identify multiple failures, their identification of worst-consequence rather than worst-risk scenarios, and their focus on a single node. These weaknesses are identified and described in this paper to assist in the development of improved approaches.

Conventional wisdom holds that the Hazard and Operability (HAZOP) study is the most thorough and complete PHA technique. Arguably, it is the most commonly-used PHA technique in the world today. However, the method is not without its own weaknesses, some of which are not generally recognized. Therefore, a critique of the method is provided to assist in specifying criteria for improved methods. Amongst the weaknesses discussed for the HAZOP study method are the extent to which design intent can be defined and considered, completeness of parameter selection, efficiency in identifying hazard scenarios, the counter-intuitive inductive / deductive starting point, and the difficulty in focusing on specific hazard types.

Key criteria to guide the development of improved methods are proposed and discussed in the context of newer PHA techniques such as Major Hazards Analysis that have been developed to address the limitations of classical methods such as the HAZOP study. These key criteria include a structure that facilitates meaningful brainstorming of scenarios, ease of understanding and application of the method by participants, ability to efficiently identify scenarios, completeness of scenario identification, exclusion of extraneous scenarios, ease of revalidation of studies, and ease of meeting regulatory requirements.