Definition(s)

Safe State

state of the process when safety is achieved

Note 1 to entry: Some states are safer than others (see Figures B.1, B.2 and B.3) and in going from a potentially

hazardous condition to the final safe state, or in going from the nominal safe condition to a potentially hazardous

condition, the process may have to go through a number of intermediate safe-states.

Note 2 to entry: For some situations, a safe state exists only so long as the process is continuously controlled. Such

continuous control may be for a short or an indefinite period of time.

Note 3 to entry: A state which is safe with regard to a given safety function may increase the probability of

hazardous event with regard to another given safety function. In this case, the maximum allowable spurious trip

rate (see 10.3) for the first function should consider the potential increased risk associated with the other function.

 

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Figure B.2 — Example of the classes of states for a 2oo3 system

 

Figure B.3 — Synthesis of states and failures taxonomy for one continuous mode safety systems
 

Source: ISO/TR 12489:2013(E). Global Standards

 

 

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