Overview of the CyberPHA Methodology
Including Visualization of the Results Using Bowties

by John Cusimano & Tim Gale

Process hazard assessments (PHA) are a well-established practice in process safety management. These assessments focus on failures (aka deviations) that are typically caused by equipment failures or human error. By design, PHAs do not consider cyber threats to industrial control systems (ICS). However, cyber threats represent additional failure modes that may lead to the same health, safety and environmental consequences identified in the PHA. Functional safety (i.e. ISA 84 / IEC 61511) and industrial cybersecurity standards (i.e. ISA/IEC 62443) recognize this issue and provide guidance on how to integrate these two disciplines to ensure that cyber incidents cannot impact process safety.


A proven methodology, called Cyber PHA, based on ISA/IEC 62443-3-2 has been developed and applied to conduct ICS cyber risk assessments throughout the process industries. This paper will describe the methodology with examples of actual applications to identify, rank and mitigate cyber risk in ICS systems. Furthermore, we will demonstrate how Bowtie Analysis can be used to visualize the results and apply degradation factors and controls related to cyber barrier assurance.

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