Using credible failure rates for SIS ensures process safety: A summary of the panel discussion

On March 13, 2023, in conjunction with the 19th Global Congress on Process Safety, four of the authors gathered to participate in a panel session. The discussion centered on the premise that many individual device failure rates published by some manufacturers and some certifying agencies are deemed—by members of the panel, many safety instrumented system (SIS) designers, and practicing engineers in the field—to be too low. This is especially true for mechanical final elements. A SIS designed using these unrealistic failure rates often results in estimated safety integrity levels (SILs) for the individual safety instrumented functions (SIFs) comprising the SIS, which would be achievable only under the most optimistic assumptions regarding installation, operation, and maintenance. These estimated SILs are unlikely to be achieved in the field. The panel discussed the underlying causes of this serious safety issue and proposed some possible solutions. This paper summarizes the panel discussion among four of the authors. Relevant graphics shown during the discussion and some panelists' quotations are included.