Abstract: Employee #1 was processing a solvent-based concrete expansion joint adhesive, manually adding a 50 lb bag of magnesium oxide powder to 700 gallons of a 90:10 toluene:xylene solution. Flammable vapors inside the ambient temperature mixing vessel ignited and Employee #1 suffered first-, second-, and third-degree burns over 25 percent of his body, including his arms, chest, shoulders, neck, and face. He was flown to Metropolitan Medical Center in Cleveland, OH, where he remained hospitalized for approximately one week. At the time of the accident, Employee #1 was wearing a short-sleeve cotton tee-shirt, blue jeans, rubber-soled work boots, and safety glasses, but no other means of personal protective equipment was being used. Subsequent investigation concluded that there were several possible sources of ignition, including: 1) The agitator drive shaft coupling: At some time during use of the mixing vessel, the coupling slipped approximately 1/4 in. from its regular operating position and came to rest on a compression fitting bolt. The rotating action of the ferrous coupling caused significant wear on the bolt and on itself. The grinding metal components were a source of frictional heat and a possible source of sparks. The coupling was approximately 13 in. away from the mixer loading hatch. 2) Static discharge: Employee #1 was having difficulty loading the magnesium oxide powder, which was inside a paper and plastic liner, so he placed the bag inside the mixing vessel and violently released the material. At the time of the accident, he was isolated from ground and the employer had not provided any means to eliminate or prevent the generation of a static charge. 3) Electrical equipment: The cover plate on the mixer motor junction box was not secured in place and was missing a gasket. One of the four bolts used to anchor the cover plate was broken in half, and another had not been tightened. During the mixing operation, vibrations from the motor could have caused the two ferrous components to rub together and generate a spark. The electrical equipment on the mixing vessel (the motor junction box and the electric motor that was missing the close-fitting journal) were not safe for the hazardous location. The electric motor was approximately 44 in. from the mixer loading hatch. 4) Smoking: The day after the accident, the plant manager and the union representative did a walk-through inspection of the unit operating area. They found several extinguished cigarette butts in the area around the mixing vessel. The fire chief, who had responded to the fire, also stated that several cigarette butts had been found in the area of the mixing vessel on the day of the accident.