Respondent operates a natural gas processing and fractionation facility. Respondent had maintenance activities performed on the Inlet Filter Separator (“Vessel”) on March 10, 2014 and March 11, 2014. The Respondent used a contractor to perform the routine maintenance on the vessel, specifically, to replace filters. The Vessel was flooded with water overnight on March 10, 2014, which cleaned residual hydrocarbons from the vessel. All of the High Point Vent Valves on the vessel were not opened prior to flooding the vessel with water. On the day of the incident, March 11, 2014, the Vessel was drained and the filters were removed. Upon returning from lunch, but before the arrival of the operator assigned to oversee the project, the contractors noted white smoke escaping from the vessel. In response to the smoke one of the four contractors sprayed water into the vessel. A pyrophoric reaction occurred inside the vessel, and the ensuing fire injured the four contractors. The fire was extinguished and the injured workers were transported to emergency medical treatment.