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(a) A simple escalator accident map. Hazards connected in the map happened in three sample cases; (b) L-space graph. The hazard chain of the Case 1 is composed by hazards (nodes) 1,2, 3,4,5, and 6; the hazard chain of the Case 2 is composed by hazards (nodes) 7,3,4, 8,5, and 6; the hazard chain of the Case 3 is composed by hazards (nodes) 8,7,3, 4, and 9.
