Definition:
Random Failure is a failure occurring unpredictably during the useful life of a component. It is not caused by a design flaw (systematic) or by a physical wear-out mechanism.
Physical wear out, such as predictable maintenance (think replacing brake pads), is managed by scheduled maintenance.
Within functional safety, all failures are either systematic or random failures.
Key Points:
- Modeled statistically using failure rate (λ).
- Inherent variability in materials, manufacturing, or operation leads to random failures.
- Mitigated or detected through redundancy, diagnostics, proof testing, and choosing reliable components.
- Past useful life, random failure is no longer a relevant concept as the component should have been replaced.
Example:
A relay contact welding shut without any prior warning during normal service is a random failure. A brake line suddenly leaking due to a rare, undetectable material flaw is a random failure.
See Also: systematic failure, failure rate, physical failure, useful life
Cited Source:
- IEC 61508-4:2010, Clause 3.6.2.
- NTNU Norwegian University of Science and Technology – training slides on failure classification