Abstract: At approximately 8:30 p.m. on October 21, 2014, Employees #1 and #2 were checking the compressed air system in Maintenance Room #1 of the 7K pellet support building. During the process of increasing the pressure into the 4-inch compressed air line from approximately 125psi to the test pressure of 175 psi a failure occurred. The pressure caused the two sections of the pipe to move or shoot out in opposite direction striking and damaging the interior wall system and puncturing the exterior pre-engineered metal building envelope. The failure broke apart a 90 degree elbow which connected a vertical pipe riser to a horizontal pipe section running overhead and perpendicular to the joists in the open ceiling area above. The failure caused the vertical pipe to disconnect from the upper fitting while the fitting at the bottom of the vertical pipe remained in position. The top of the vertical pipe riser rotated counter clockwise approximately 165 degrees striking Employee #1 on the left side of his head and Employee #2 was struck on his arm. Employee #1 was killed.