Process Safety Time Analysis for Upstream Facilities

Abstract

Per IEC 61511-1 Process Safety Time is defined as, “the time period between a failure occurring in the process or the basic process control system (with the potential to give rise to a hazardous event) and the occurrence of the hazardous event if the safety instrumented function is not performed”. This paper will discuss how Process Safety Times were categorized, evaluated, and verified in order to comply with the standard and on a upstream mega project containing over 580 Safety Instrumented Functions, 350 of which were rated SIL 1 or higher. In the past, the practice has been to assign general overall values to Process Safety Times, many times for an entire project or possibly for individual units in a process facility. On our recent mega project, our client challenged the engineering team to develop more customized values based on individual processes. Our expectation is that in the future this expectation will grow more stringent and focused. Our control systems and process engineering teams will have to work together to develop the necessary work processes and methods to generate, justify, and report these critical time values.