Abstract: Employees #1 and #2 were standing on a 2 ft by 35 ft by 8 ft high platform cleaning a resin storage tank. The tank had been soaked with MEK for a month and a half. The employees drained the MEK from the tank and poured 10 gallons of toluene into a job-made pneumatic-powered circulating pump. They then added another 5 gallons of toluene. The ventilation fan on the roof and the flashlight Employees #1 and #2 were using to see inside the tank were not designed for class 1B flammable atmospheres. In addition, no grounding/bonding straps or cables were attached to the tanks and the ventilation system and the hoses were not self-bonding. A galvanized fitting was attached to the end of the hose on the circulating pump to reduce the opening and provide more pressure. An unknown source caused the tank to explode and catch fire. Employees #1 and #2 were killed. Employee #3, who was helping Employees #1 and #2 clean the tank, was hospitalized. Employee #4, who was also working in the area, was treated and released. It could not be determined what actually caused the spark that initiated the explosion and fire.