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PT Notes

Hazards Addressed by Process Safety

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.

The purpose of OSHA’s Process Safety Management (PSM) standard is “... preventing or minimizing the consequences of catastrophic releases of toxic, reactive, flammable, or explosive chemicals. These releases may result in toxic, fire or explosion hazards”. A catastrophic release is defined as a major uncontrolled emission, fire, or explosion, involving one or more highly hazardous chemicals that presents serious danger to employees in the workplace. “Serious danger” is not defined in the PSM standard but presumably it is intended to cover the possibility of fatalities and serious injuries but not lesser consequences.

Given this purpose, the hazards usually addressed in PHA are those of fire, explosion, toxic release, and reactivity arising from covered chemicals, that is, the highly hazardous chemicals defined in the standard. However, the PSM standard simply states, “The process hazard analysis shall address the hazards of the process.” Consequently, it is important to decide what hazards should be included. The following issues should be considered:

  • Covered chemicals may have hazardous properties besides flammability, explosivity, toxicity, and reactivity. For example, they may also be corrosive.
  • Processes containing covered chemicals may release toxic or otherwise hazardous materials which are not themselves covered chemicals.
  • Incidents involving covered chemicals may release toxic combustion products or toxic products of thermal decomposition that are not themselves covered chemicals.
  • Non-covered process chemicals in a covered process may pose hazards, e.g. asphyxiation from plant nitrogen.
  • Hazards may also be posed in a covered process by:
     Process materials, e.g. scalding from process steam.
     Process equipment, e.g. pinch points.
     Process conditions, e.g. high pressure.
     Process situations, e.g. hot surfaces.
     Maintenance activities, e.g. welding.

These hazards may be addressed by other OSHA regulations, and are covered by the General Duty clause. For hazards not associated with PSM-covered chemicals, for example, slips and falls within a PSM-covered process, and for situations that do not result in a release of a highly hazardous chemical, a straightforward case can be made for their exclusion from PHA studies. At issue is whether all hazards associated with covered chemicals should be included. Given the stated purpose for PHA in the PSM standard, it seems clear that only toxic, reactive, flammable, and explosive hazards should be addressed so that other hazards, such as corrosivity, can be excluded. However, while the release of toxic combustion or decomposition products from covered chemicals is not specifically addressed by the PSM standard, companies may wish to include them in PHA studies.

Some companies do not explicitly specify the types of hazards to be addressed by their PHA studies but leave it up to each PHA team. This is a dangerous practice because each team may make different decisions, even when the same covered chemicals are involved. Such inconsistencies may result in regulatory and/or legal liabilities. In particular, if a team decided to include a hazard, say nitrogen asphyxiation, in one study, but other study teams did not, then a regulator or prosecutor could make the case that the company was remiss for not ensuring that nitrogen asphyxiation was covered in all studies. Even worse is a situation where a PHA team includes a few nitrogen asphyxiation scenarios in a study because they seem particularly important but does not look systematically for all such scenarios as the team knows they are not a primary objective of the study. It can then be argued that the PHA study is defective because it is incomplete. If a nitrogen asphyxiation incident that had been omitted from the study were to occur subsequently, the company would be in a very difficult situation.

It is important that company PHA guidelines specify what types of hazards should be addressed in studies. Also, the specific hazards to be addressed should be specified for each individual study in the purpose, scope, and objectives statement for each study.

Requirements for PHA studies are addressed in these publications:

Analytical methods in process safety management and system safety engineering – process hazards analysis, Handbook of Loss Prevention Engineering, Wiley-VCH, 2013.

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.

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