A risk perspective for emergency pressure relief system design

Abstract

Improperly sized pressure relief devices have historically been a factor in a significant fraction of serious accidents involving process reactions. The Design Institute for Emergency Relief Systems (DIERS) efforts have provided a methodology which minimizes the potential for inadequate pressure relief capacity. Unfortunately, this methodology can lead to requirements for vent sizes which appear to be unreasonably large. The difficulty may be traceable directly to the selection of the design basis. It is often difficult to justify credible bounds for scenarios to be considered in the design by qualitative methods alone. In these instances, quantitative risk assessment methods can be effective in providing criteria for the elimination of excessive conservatism and thus can lead to a satisfactory design. This paper describes a hypothetical but realistic example which effectively combines the DIERS methodology with quantitative risk assessment methods. The result is a more satisfactory basis for evaluating the adequacy of the vent design.