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PT Notes

Importance of Defining the PSO for PHA Studies

 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.

Process hazard analysis (PHA) studies must have a well-defined statement of purpose, scope, and objectives (PSO) to be effective and efficient. A PSO statement is essential to ensure that PHA studies are focused and complete. It defines what must be addressed but also constrains studies to appropriate content. It helps to avoid the inclusion of extraneous items and digressions during study performance. An incomplete study can create regulatory and legal liabilities and digressions waste valuable time. Preparation of a PSO statement prior to the performance of a PHA study, and use of it during the study, is good practice.

The purpose is the reason why the study is performed, for example, to meet regulatory requirements or company standards. It affects the way a study is performed, for example, the types of hazards to be included and the types of consequences to be addressed. Its definition helps to ensure the study outcome is consistent with the intention for the study.

The scope addresses what is included in the study. It may also address what is not included. Items to consider including in the scope statement are:

  • Process boundaries
  • Equipment, procedures, control systems, etc.
  • Utilities / support systems
  • Modes of operation
  • External events
  • Level of detail
  • Level of causality
  • Design intent
  • Codes and standards
  • Exclusions
  • Assumptions

Objectives define what is to be considered, specifically, the types of hazards and consequences.

Processes pose a wide variety of hazards. Decisions must be made on whether the study will address:

  • Only major hazards associated with chemicals covered under applicable regulations.
  • Other types of hazards from covered chemicals, such as corrosivity.
  • Hazards from non-covered chemicals such as raw materials, intermediates, products, by-products, additives, catalysts, and waste streams.
  • Hazards from other process materials, equipment and conditions, such as nitrogen asphyxiation, scalding from steam or hot oil, or exposure to hot surfaces or materials, cryogenic materials, pinch points, hose whipping, high pressures, high static or kinetic energy, vacuum, pressure cycling, temperature cycling, or high voltage or current.

A decision also must be made on which types of consequences will be addressed in the study. The study may focus on regulatory issues and address only safety impacts on employees and the public, and environmental impacts. However, it may also address other issues of importance to the company such as operability, process downtime, property damage, and product quality. The consequences that must be addressed are determined by the study purpose. All consequences required by the study purpose must be included.

The PSO statement will vary from one process to another, although there will be commonalities. Processes at the same facility likely will share similar purposes and objectives but scope statements will vary. Aspects of the PSO statement may vary depending on the phase addressed in the process life cycle.

The PSO statement should be referenced and used during the PHA study to keep the team on track, ensure appropriate study content, ensure the study is complete, and help avoid team members raising issues that are not relevant. The statement provides a means of quality control to ensure that all required issues are addressed and issues not of concern are excluded.

The performance of PHA studies requires considerable resources, time, and effort and PHA studies are of vital importance in helping to ensure the safety of processes. Consequently, it is essential that every effort be expended to ensure they are conducted effectively and efficiently. The preparation of a PSO statement is critical for accomplishing this objective. The statement helps to constrain PHA studies to what is required and provides a means of helping to ensure they are complete.

This topic is discussed in greater detail in the article:

The importance of defining the purpose, scope, and objectives for process hazard analysis studies, Process Safety Progress, Volume 34, Issue 1, pages 84 - 88, March, 2015.

The paper can be accessed for free by clicking on the link:


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Click on the links below for information on related training courses:

PHA for Team Leaders

Advanced PHA for Team Leaders

Managing Psychological and Human Aspects of PHA Facilitation

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