The determination of alarm setpoints should consider the trade-off between the timely alerting of an operator to off-normal conditions and the creation of nuisance alarms caused by establishing setpoints so close to the "normal" operating values that occasional excursions of no real consequence are to be expected.
Additional Information:
When determining setpoints, consideration should be given to the performance of the overall human-machine system (i.e., operator and alarm system acting together to detect process disturbances). If setpoints are established such that many false alarms occur, operators become less likely to respond to the alarm, especially when their tasks become cognitively demanding. Processing techniques (see Guideline 4.1.2-4) are applied to prevent normal variation from producing alarms. Under some circumstances, however, preventing such alarms may deprive operators of needed information. In cases where raising an alarm's setpoint or delaying its presentation is not acceptable, more sophisticated techniques (e.g., alarms based on rate of change of the parameter or the time at which the parameter is projected to exceed a setpoint) should be considered.