Abstract: A five-man crew was in a tunnel disassembling the shield on the metro rail B251 project. Employee #1, the supervisor, Employees #2 and #3, and two coworkers were members of the disassembling crew. Employee #3 was cutting a tubular hose bracket using a welding torch. The tubular bracket, weighing about 270 lb, was dropped from a height of 10 ft, puncturing an acetylene cylinder stored directly below. The punctured acetylene cylinder instantaneously caught fire. The flame from the burning cylinder impinged on the side of another cylinder, causing that cylinder to explode. Employees #1, #2, and #3 were burned in the explosion and all three required hospitalization. The tubular frame that was cut was not chained and the gas cylinders were stored improperly, directly below the cutting area.