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Keywords:

  • layers of protection analysis;
  • risk analysis;
  • consequence;
  • quantitative

Abstract

Most risk analysis methods rely on a qualitative judgment of consequence severity, regardless of the analysis rigor applied to the estimation of hazardous event frequency. As the risk analysis is dependent on the estimated frequency and consequence severity of the hazardous event, the error associated with the consequence severity estimate directly impacts the estimated risk and ultimately the risk reduction requirements. Overstatement of the consequence severity creates excessive risk reduction requirements. Understatement results in inadequate risk reduction.

Consistency in the consequence severity estimate can be substantially improved by implementing consequence estimation tools that assist process hazards analyses/layers of protection analysis (PHA/LOPA) team members in understanding the flammability, explosivity, or toxicity of process chemical releases. This article provides justification for developing semiquantitative look-up tables to support the team assessment of consequence severity. Just as the frequency and risk reduction tables have greatly improved consistency in the estimate of the hazardous event frequency, consequence severity tables can significantly increase confidence in the severity estimate. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2012