11.1 The FMEA study in general only analyses failure
effects based on a single failure in the system and therefore a failure
detection means, such as visual or audible warning devices, automatic
sensing devices, sensing instrumentation or other unique indications
shall be identified.
11.2 Where the system element failure is non-detectable
(i.e. a hidden fault or any failure which does not give any visual
or audible indication to the operator) and the system can continue
with its specific operation, the analysis shall be extended to determine
the effects of a second failure, which in combination with the first
undetectable failure may result in a more severe failure effect, e.g.,
hazardous or catastrophic effect.