What does the double contingency principle require for criticality safety?

What does the double contingency principle require for criticality safety?

• A. One improbable deviation
• B. Two independent, improbable deviations
• C. Two independent probable deviations
• D. No deviations needed

Answer: (B)

In criticality safety, two independent, improbable deviations are required before a configuration could become critical. This means two separate changes from normal conditions must occur, each unlikely and not caused by the same factor, for criticality to be possible. The idea is that a single error or a single control failure cannot by itself push the system to critical; you need a second, independent change to happen as well. This is often implemented by designing safeguards so that two separate conditions or barriers must both be overcome to reach criticality, making the probability of an accidental event extremely small. If only one deviation were needed, a rare mistake could still lead to a dangerous state; if no deviations were required at all, the system would not be safe.

In criticality safety, two independent, improbable deviations are required before a configuration could become critical. This means two separate changes from normal conditions must occur, each unlikely and not caused by the same factor, for criticality to be possible. The idea is that a single error or a single control failure cannot by itself push the system to critical; you need a second, independent change to happen as well. This is often implemented by designing safeguards so that two separate conditions or barriers must both be overcome to reach criticality, making the probability of an accidental event extremely small. If only one deviation were needed, a rare mistake could still lead to a dangerous state; if no deviations were required at all, the system would not be safe.