failure, occurring in a random way
Note 1 to entry: A random failure may be time or demand dependent. Whether it occurs or not is not predictable
with certainty but the corresponding failure rate (see 3.1.18) or probability of a failure due to demand (see 3.2.13)
may be predictable and this allows probabilistic calculations.
EXAMPLE Examples of failure mechanisms leading to unpredictable failure occurrence are: hardware
random failures resulting from degradation mechanisms; human random failure resulting from error in routine
operation, lack of attention, stress, tiredness, etc
Note 2 to entry: From the probabilistic point of view, the random failures are the contrary of systematic failures
(see 3.2.17) which occur in a deterministic way (i.e. with a probability equal to 1) when some conditions are met.
Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards