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An analysis of CSB investigation reports concerning the hierarchy of controls


  • This work was supported by Natural Sciences and Engineering Research Council.


Sixty-three reports, studies, and bulletins resulting from process incident investigations conducted by the U.S. Chemical Safety Board (CSB) have been analyzed for evidence of examples related to inherent safety, passive and active engineered safety, and procedural safety. These risk reduction measures, which collectively form the hierarchy of safety controls, were also analyzed for their contribution to both incident prevention and consequence mitigation.

Over 200 examples from the hierarchy of controls were identified with the following breakdown: inherent safety (36% of total overall examples), passive engineered safety (8%), active engineered safety (14%), and procedural safety (42%). Numerous examples for both prevention and mitigation measures were found during the CSB report review. Inherently safer design (ISD) items were observed to be nearly equally split among the four primary principles of minimization (25% of total ISD examples), substitution (22%), moderation (25%), and simplification (27%). Widely applicable process safety management elements (in terms of a link to the identified hierarchical safety measures) were determined to be process and equipment integrity, training and performance, process knowledge and documentation, capital project review and design procedures, and management of change. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011.