Are your safeguards fast enough to be effective?

摘要

A core attribute of all safeguards is that they must be functional against the loss event in question and one of the essential elements of functionality is speed. How to determine the response time available for a given safeguard to complete its action is a common project question. Several instrumentation and controls design pitfalls should be avoided when specifying the response time. A variety of engineering practices, from basic to advanced, may be used to justify the selected value. Among these are: 1. Expert judgment, 2. Extrapolation, 3. Mass and energy balance calculations, 4. First principles process modeling. Key technical issues include hardware response lags, process lags, application program delays, measurement error, and the design and safety margins. Careful attention to this specification is needed from the instrumentation and controls design team, for if an instrumented safeguard performs too slowly compared to the hazardous event, it provides no protection at all.