The aging rubber ring led to gas leak that caused the gas cylinder explosion at a restaurant in Beijing Friday morning, local work safety authorities said Monday.

Two screw threads of a connector between the liquid gas storage tank and the evaporator were oxidized, which led to the gas leak, said Yao Meng, deputy head of Xicheng District Work Safety Administration.

Sixteen people were injured in the explosion around 9 a.m. Friday at Semi Gopur restaurant at Xinjiekou East Street, including three restaurant employees and 13 passers-by. Most of them were slightly injured.

The 16 injured are receiving treatment in Jishuitan Hospital.