Failure, Fault, and Error
Section 06: System Safety & Functional Safety
Definition
Three related but distinct concepts in system safety. A failure is the inability of a system, subsystem, or component to perform its required function within specified limits. A failure is an event — the transition from a working state to a non-working state. A fault is an abnormal condition or defect at the component, subsystem, or system level that may lead to a failure. A fault is a state — a latent or active deficiency in the system. An error is a design mistake, an incorrect action, or an unintended deviation in specification, development, or operation that may cause or contribute to a fault. Errors are causes (often human), faults are states (often latent), and failures are events (observable loss of function).
Where This Shows Up
Understanding the distinction between error, fault, and failure is critical for effective safety analysis. Errors (such as a software coding mistake) create faults (such as incorrect logic in the code). Faults remain latent until activated by specific conditions, at which point they manifest as failures (loss or malfunction of the function). Safety assessment must account for all three levels: error prevention through development assurance, fault tolerance through architectural design, and failure mitigation through safety features.
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Related Terms
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