Abstract: At approximately 11:00 p.m. on May 26, 2007, a flash fire occurred during flowback on a well completion project. The fracturing of the well was completed at approximately 3:00 p.m. the afternoon of May 26. The personnel on site were in the process of flowing back the fracturing fluid, sand and water. The fracturing fluid coming out of the well was being piped into an open top, flat tank where it was filtered to remove the sand. From the "flat tank", the water was being pumped into enclosed storage tanks. The fracturing fluid being pumped out of the well was saturated with methane. The company supervisor was aware of the process. Prior to the fire, a diesel generated light tower was brought to the area of the "flat tank". The generator wouldn't start, so the company supervisor made the decision to jump start it by utilizing one of the sub-contractors pick-up diesel truck. The light tower was positioned approximately 35-40 feet from the "flat tank". The jumper cables were hooked up, and the light generator preheat switch had been activated. The preheat functions were similar to a "glow plug". At this time, the company supervisor saw blue flames on the ground between the light tower and the flat tank. A flash fire then occurred as vapors rising from the flat tank ignited. Seven employees were injured. Two were treated for burns and released, while the other five were hospitalized. Three of the burned employees were taken to Ramsey Burn Center in St. Paul, MN.