A building’s automatic fire sprinkler system consists of a water sprinkler, installed into the building’s ceiling, as well as two smoke detectors, plus other components mentioned below. The purpose of the system is to automatically activate the sprinkler when a fire is detected by either of the smoke detectors. Sprinklers and Pump When a fire is detected, the system activates a water pump, to feed water to the sprinkler. If the sprinkler’s nozzle is not blocked and the water pump is activated, water will flow from the sprinkler. Smoke Detectors The system employs two smoke detectors to detect fires. Each is designed to act as a redundant back-up for the other: a fire is detected if either of the detectors is triggered (that is, if either of the smoke detectors detects smoke). Safety condition A hazard occurs when there is smoke but water does not flow from the sprinkler system. Suppose you have been asked to perform a fault-tree analysis on this system, for this hazard.   The top-level event (i.e. the root) for the fault tree is the case in which there is smoke but water does not flow from the sprinkler system. The following components in the system can each fail, and are assumed to fail independently of each other. These failures constitute the basic failure events (i.e. the leaves) of the fault tree: The smoke detectors (each of which fails independently of the other) The water pump The sprinkler nozzle (by becoming blocked) For each of the fault-trees below, decide whether it is correct or incorrect for this scenario and hazard. Fault Tree 1 is [ Select ] Correct Incorrect Fault Tree 2 is [ Select ] Incorrect Correct Fault Tree 3 is [ Select ] Incorrect Correct Fault Tree 4 is [ Select ] Correct Incorrect    多重下拉选择题