An operator and two servicing companies' failure to control a North Dakota oil well properly led to a flash fire that killed one worker and injured three others, federal investigators have found.

A 52-year-old employee of Most Wanted Well Service suffered fatal fall injuries and burns in the June 18, 2016 incident at a Watford City, North Dakota well site. Two other Most Wanted employees and a worker employed Sherwood Enterprise also suffered severe burn injuries. That worker was operating a service rig and tripping pipe out of the well during a snubbing operation when the incident occurred.