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PT Notes

Dangers of Using PHA Templates

PT Notes is a series of topical technical notes on process safety provided periodically by Primatech for your benefit. Please feel free to provide feedback.

PHA studies identify hazard scenarios for processes in order to determine the need for measures to reduce the risks to tolerable levels, for example, by employing the hazard and operability study (HAZOP).

Many companies employ a standard approach for performing PHA studies for all their processes. Consequently, study templates often are employed using PHA software. The templates may contain customized items such as data fields, protocols, etc.; master lists of team members, documents, safeguards, etc.; checklists of parameters, deviations, causes, etc.; a defined risk ranking scheme; and specific report formats. Such customization of studies helps to ensure both consistency and quality of studies.

Additionally, practitioners commonly enter data such as lists of process nodes, drawings, procedures, and other documents, and information such as the study charter into a project file generated from the company’s standard template. These data are shown to and reviewed by team members, typically at the beginning of the first study session and any needed revisions are made.

Such use of study templates is appropriate and valuable in helping to ensure efficient, effective, and consistent studies. However, it is possible to take the use of templates too far.

One approach that some practitioners have been tempted to use to speed up studies is to create templates containing what are viewed as common scenarios for similar process plants and equipment and to focus attention in study sessions on “one-off” scenarios specific to the process under study. However, even apparently common scenarios for similar processes can pose quite different characteristics and risks due to differences in operating and maintenance practices, process conditions, and the operating environment. Such differences are unlikely to be addressed properly if templates with common scenarios are used.

Current PHA methods depend on brainstorming by team members whose essential role is to identify hazard scenarios for the process using their process knowledge and expertise. Scenario identification depends on the synergistic interaction between team members. Providing common scenarios identified by one team to another team effectively divides the team for a study into two groups which eliminates the possibility of synergistic interactions needed to flush out the details of scenarios. The second team does not have the insights into scenarios possessed by the first team who identified them. Furthermore, when presented with so-called common scenarios, the natural tendency of teams is simply to accept that they are the same as for other processes and not recognize the differences.

The use of common scenarios in templates trades study speed for quality. The result is apparent consistency across PHA studies for similar processes but at the expense of not properly characterizing scenarios for the processes and impairing the identification of appropriate risk reduction measures, which is the principal purpose of PHA.

Certainly, PHA studies should be compared for similar processes as part of quality control practices for PHA. Data analytics can be used for this purpose. However, use of common scenarios as part of study templates likely will lead to higher process risks than desired and consequently is poor practice.

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