Instrumentation Reference Book, 4th Edition

43.6. Safety Monitoring

43.6.1. Types of Failure

Hitherto we have considered that a fault in a component occurs when its characteristics change enough to prevent the system in which it is incorporated from producing the expected output. The only categories which have been recognized are those dealing with changes with time—permanent or intermittent faults—and those dealing with the rate of change—degradation or catastrophic failures. For example, both open-circuit and short-circuit failures are regarded equally as catastrophic failures. This classification is valid for all data handling systems, but needs further refinement for some control systems and safety monitoring systems.

In these we can envisage two consequences of failure, depending ...