Abstract: At approximately 2:18 p.m. on February 25, 2009, a company was unloading tank trucks filled with wastewater. The wastewater was collected from gas-well drilling and rainwater from diked areas of an industrial plant in Pennsylvania. Because the water was used to lubricate drill bits and carry away rock fragments, it had chemical additives to prevent drill corrosion, lubricate the drill, and stop bacterial growth in the rock formation. Thus, the water had to be treated before disposal. Employees would unload the trucks by placing them close to the outside wall of the facility and connecting the truck-discharge hoses to pipe fittings on the outside wall of the plant. The liquid was pumped into one of three large open-topped holding tanks located at the rear of the building. The trucks were pumping, and an employee heard someone turn on the vent fan. The employee, who was on the floor near the holding tanks, saw a black cloud near floor level. He started up the ladder to try and look into the holding tank and felt it getting hotter. He got off of the ladder and started running to get out of the building when was knocked off his feet by at least two explosions which ignited his clothing. Other workers in the plant assisted him, and the fire department arrived and used foam to dowse a fire in the holding tanks. The employee was hospitalized with burns on his arm, back, face, and chest. The building was heavily damaged, and most of the equipment was destroyed. Electric equipment in the area had not been approved for Class 1, Division 1, or Class 1, Division 2, locations.