Given that "critical" will probably endure as a named condition, though in confusing permutations, let's consider one more attempt to clarify and simplify its use.

Safety and cost drive all PM while safety and economics drive all plant operations. Ignoring economics fails to adequately address our sole operations purpose. For this reason, "economically critical" is an acceptable concept-provided we restrict its application to failures. The primary consequence of most safety equipment failures are operational; we must terminate operations to address a key safety function. Using our functional definition of failures, we could agree to use another term for equipment classification based upon economics, then reserve the term "critical" for safety functions and their failures.

We would then have two classes of equipment important and non-important and a sole criteria for classification: whether we plan to consider scheduled maintenance for the item or not. We could just as well identify these as "scheduled maintenance" and "non-scheduled maintenance." Once past this barrier, we can review equipment for applicable and effective PM tasks.

Practically, a reviewer looks at the following identifiers to discern suitability of scheduled maintenance:

• equipment size

• failure reporting frequency

• work frequency (including PM)

• vendor recommendations

• general industry practice

• shop practice

• equipment register

Equipment size. Large equipment is expensive. Safety considerations are based upon enclosed energy and fluids. Large items are always reviewed for PM activity. In addition, since the work scope involved in opening large equipment is considerable, they're expensive to maintain. Documented PM or maintenance costs...