Abstract
The human role is key to process safety and the control of risks, necessitating the inclusion and quantification of human actions as part of safety barriers. Incorporation of human action as a barrier component in risk analysis studies is recognized as an important, though often challenging aspect of the analysis. The non-consideration of human actions and interventions as safety barriers is a very conservative approach and could lead to unjustified expenditures to reduce risks by implementing additional hardware barriers or require more stringent performance levels on other barriers.
Existing methods for assessment of human error probability are, or very coarse (use of generic literature data, addressing only part of the human response loop), or very complex (for example SPAR-H, Petro HRA). A more pragmatic method for estimating the reliability of human response, addressing all components of the human response loop and their performance shaping factors, has therefore been developed. This method, called HEPIRA (Human Error Probability in Responding to safety Alarms), is a procedure for quantitative evaluation of the human error probability by operators in responding to critical process and fire & gas alarms, that intervene in the prevention or mitigation of a major accident scenario.
In HEPIRA, a qualitative review of 26 conditions allows to evaluate the performance of the measurement or detection system, the alarm visualization and observation and the effectiveness of event diagnostics, decision-making, as well as the execution of the required corrective action to stop the scenario from developing. These conditions have a varying level of criticality and their relevancy to the scenario depends on the complexity of the event and of the required corrective action. The application of the procedure results in a Probability of Failure on Demand ranging from 1 to 10-2.
