Abstract: On March 2, 2006, Employee #1, a welder, was torch cutting on top of a 12,000 gallon carbon-steel tank in a hazardous waste treatment, storage, and recycling facility. The tank, which had a cone bottom and was about 28.5 feet above the ground, had previously held solvent contaminated wastewater. An Industrial Scientific Corporation multi-gas monitoring instrument, Model Number 140, Serial Number 0312193-005, equipped with a sampling pump, Serial Number 05120XW-025, and 6.5-foot tubing, entering the tank from an 8-inch top hatch, was used to monitor the atmosphere inside the tank. As Employee #1 was kneeling next to the top hatch of the tank, on the walkway above the tank, torch cutting through the top of the tank, a fire occurred. Flames came out of the top hatch and caught his clothes on fire. Employee #1 was hospitalized approximately six hours later, where he was treated for second and third degree burns on his buttock and perineum area. Employee #1 was wearing a personal fall arrest system to include a body harness and shock absorbing lanyard, which allowed him to reach outside the guarded walkway. The accident investigation revealed that the accident was caused by inadequate preparation of the tank for hot work. Although the tank had been steam cleaned prior to the welding operation, the tank was neither isolated nor purged. Additionally, there was insufficient monitoring of the tank atmosphere. The employer was issued two serious violations, prohibiting their engagement in activities requiring the use of direct air monitoring equipment, as well as welding operations.