On 15th of July at 16:00 hrs; A Roustabout was standing on the pipe ram BOP at a height of 1.57 m shaking the flexible hose joint of the flowline (suspended by 2 web slings on a crane) in an attempt to slide the flowline out of the vent line connection on the shaker tank. The flowline came out from the vent line end and swung in the direction of the Roustabout, who lost his balance while trying to avoid it and fell down approx. 0.5 m, His fall was arrested by the fall arrester connected to his full body harness. He sustained fracture on his left hand little finger when he was struck by the wing nut of the flowline connection against the annular BOP body.