Critical safe operating parameters: “Never exceed” limit and “never deviate” action



Where does the human being fit in the normal operating system and where does he/she fit in the safety shutdown system? Planning ahead can make human interaction inherently safer. This paper offers the following suggestions for managing that interaction: (1) Use inherently safer principles in the design of the process and its layers of protection. (2) Define “Never Exceed” limits for critical safe operating parameters. (3) Define a mandatory action point and a “Never Deviate” action with enough response time to prevent exceeding the Never Exceed limit. (4) Train and drill.