This type of maintenance is justified whenever a failure is not evident under normal circumstances or cannot be detected through routine preventive maintenance tasks. Also, functional checks are justified when:
there is no way to prevent the malfunction (and therefore any possibility of preventive maintenance is excluded);
tests and screenings can be performed without this implying any changes to the normal functioning of the building;
the risk of a “hidden” malfunction in a given system is high;
the probability of the tests causing a serious malfunction is very low;
the cost of failure fiding tasks is lower than the cost of corrective maintenance.