An interesting question arose recently when creating an FSM plan:

Does the ISA-18.2 standard on alarm management address the claiming of the operator’s response to alarms as a layer of protection?

Not specifically, however the ISA-18.2 standard does require that alarms are rationalized, and that alarm system performance is measured and judged against recommended metrics. Both activities in the alarm management lifecycle directly impact the dependability of the operator’s response to alarm as an IPL. Remember, an IPL must be:

• Specific
• Auditable
• Independent
• Dependable

An unrationalized system is likely to have too many alarms, incorrect priorities, and alarms without an operator response. A system without a monitoring and assessment program is likely to have nuisance alarms, alarm floods, alarm overload, and frequently occurring alarms. These issues impact the operator’s ability to detect, diagnose, and respond to all alarms - which increases the probability of failure on demand for an alarm claimed as an IPL.

Overall, this means operators working with an unrationalized system, or one that performs poorly, are more likely to miss that “all important” safety IPL alarm (or respond incorrectly). Thus I would recommend that additional criteria be considered:

• The alarm system is/shall be rationalized
• Alarm system performance shall be measured and deemed acceptable

Read more about how to make the most of alarms as a layer of protection.