Complex sentence: Because the lading was not properly secured, a portion fell from the car while in transit, damaged the westward passenger track sufficiently to cause the derailment of No.5 which in turn caused the derailment of Extra 1736 West.
Split into simpler sentences: Because the lading was not properly secured, a portion fell from the car while in transit. The track was sufficiently damaged to cause the derailment of No.5 which in turn caused the derailment of Extra 1736 West.