Driving Consistency in the Estimation of Severity Levels in PHA Studies | AIChE

Driving Consistency in the Estimation of Severity Levels in PHA Studies


Conference Presentation

Conference Type

AIChE Spring Meeting and Global Congress on Process Safety

Presentation Date

April 1, 2014


30 minutes

Skill Level




Driving Consistency in the Estimation of Severity Levels in PHA Studies

Marc Guindon,a  Chris Wells,a  Rich Piette,a Greg Knight,b  and Gary Fitzgeraldb


aSuncor Energy, 150 – 6th Avenue S.W., Calgary, AB, T2P 3E3

bABS Consulting, 140 Heimer Rd., Suite 300, San Antonio, TX, 78232

This paper outlines a methodology and associated tool to estimate the consequence severity level for several hazard scenarios associated with a variety of hazardous materials.  The purpose of this methodology is to drive more consistency in the determination of the consequence and likelihood so that risks can be compared across the organization.

During the course of PHA studies, team members are required to categorize the severity level for releases of hazardous materials associated with various cause/consequence pairings.  If the assessment of severity level is performed in a “qualitative” fashion there is the potential that the team may either overstate or understate the impact of a release which will result in inaccuracies in the risk assessment.  This may be due to differing perceptions or experience levels of PHA study teams.

In the absence of detailed consequence analysis modeling for a given release scenario, PHA study teams may elect to utilize a table similar to the one provided in Table 3.1 – (Example Consequence Categorization) contained in the CCPS concept book “Layers of Protection Analysis”.   Alternatively tools such the Dow F&EI or CEI tools can be utilized to estimate the severity level.  However all of these tools have limitations in their ability to properly assess severity levels for operating units with differing levels of process congestion or population density, etc… This may result in inaccurate categorizations of severity levels.

The proposed methodology and associated tool estimates the severity level for flash fire, vapour cloud explosion, jet fire, pool fire, and toxic exposure consequences for various hazardous materials.  The assessment tool uses a fundamental set of input parameters to assess the worst credible consequence severity level and likelihood to determine its inherent risk (prior to the application of safeguards) for a given release.

Using some basic Process Safety Information associated with the release scenario and the process unit under study, the PHA study team is able utilize the tool to obtain the worst credible consequence category as well as the inherent risk.  The study team can then proceed with the application of safeguards to determine the residual risk (following the application of safeguards) and the need for any recommendations to reduce the risk for the associated scenario.


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