Abstract: On January 28, 2002, Employee #1, a worker with a tank overhaul and repair company, was cleaning a truck tank used to haul crude oil for a company that overhauls tankers used by trucking companies to haul liquids on the highways. Employee #1 was using a "spinner" (an electromechanical device that uses steam under pressure to clean the inside of the tank) and was standing on top of the tank when vapors ignited and exploded inside the tank. He was thrown into the air and landed several feet away from the tank. He suffered no serious burns, but had a separated shoulder, twisted ankle, and facial lacerations. He was transported to the hospital in a coma, but recovered consciousness and was discharged three days later. The spinner would set on top of the tank. It was powered by a 24-volt motor, which was not intrinsically safe and was located on top of the tank. A rod passed through a rubber stopper into the tank. Steam was forced through the rod at 800 to 1,000 lbs per square in. (PSI), and it rotated to direct the water in all areas of the tank. The usual procedure was to initially monitor the tank with a calibrated meter to measure lower explosive limits (LEL), and, if any flammable vapors were found, the tank was flushed with water or air as needed until the interior of the tank was inert. Records were kept of LEL measurements. If the tank did not show any LEL concentrations, it was not rechecked until the next time the tank is worked on or in. Employee #1 stated that he followed the procedure. It was a cold and wet morning, and he has previously observed that as the steam heats the tank, vapors come off from the residual crude oil. When he removed the spinner from the tank section, he saw sparks coming from it and then the explosion occurred. The employer was cited for a serious accident-related violation of 8CCR, section 5420 (a) (2), namely (1) the spinner was not intrinsically safe, thus, was a source of ignition introduced to the explosive zone, and (2) the employer did not require frequent tests of the LEL to determine if the environment was changing (especially with the introduction of heat) and if the quantity of gas released was rising to the point that the LEL was reached.