Main Description |
An FTA uses logical operators (commonly AND, OR, and NOT, but may also include XOR, NOR, and NAND) to depict the
explicit relation between normal and exception (i.e. error) conditions and normal and exception (i.e. failure) events.
FTA can be used to depict the causal chain of events and conditions for an existing design and also drive the
development of design approaches (called control measures) that address the safety issues. These control measures are
then added to the FTA as "ANDing redundancy" so that for the hazard to be manifest, both the original condition or
fault must occur AND the control measure must fail as well.
An FTA is most often used in a top-down fashion, beginning with the hazards and the discovering that underlying faults
that can lead to them. In contrast, an Fault Means and Effect Analysis (FMEA) is most often used in a bottom up
fashion, beginning with the failures and then determining the consequences. Both are used in reliability and safety
engineering.
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