2011年7月5日上午,北京地铁4号线动物园站因上行电动扶梯发生设备故障,造成1名12岁少年身亡、3人重伤、27人轻伤。经初步调查,市质监局表示,导致事故的直接原因是“固定零件损坏,扶梯驱动主机发生位移,造成驱动链条脱落,扶梯下滑”。 On the morning of July 5, 2011, one 12-year-old was killed, 3 seriously injured and 27 slightly injured as a result of equipment failure on the escalator at the escalator in Beijing's Subway Line 4 Zoo Station. After a preliminary investigation, the Municipal Quality Supervision Bureau said that the direct cause of the accident is “the damage of the fixed parts, the displacement of the escalator-driven host, causing the drive chain to fall off and the escalator to slip”.