A task to be performed by a system, during the execution of which the system is altered such that the failure logic for the system is also altered at specified times. For example unloading a tank car consists of at least three phases: (1) connecting the tank car to unloading system, (2) unloading the tank car, and (3) disconnecting the tank car from the unloading system. An unloading hose rupture during phase 1 results in a minor operational problem. A rupture of the same hose during phase 2 (unloading) may be disastrous.
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