Abstract: On August 19, 1999, Employee #1 was conducting a routine cleaning operation on a 400 gallon Westerlin disperser/mixer. When Employee #1 inserted a scrub brush into the tank there was a flash and an explosion. The tank contained a small amount of methyl ethyl keytone. The standing operating procedure was to add an inert gas prior to beginning the cleaning operation. On this instance Employee #1 failed to do so. The nylon brush used during the cleaning operation was found to hold a static charge. As a result of this accident the employer switched to a cactus fiber brush, called Tampico, which does not hold a static charge. Employee #1 was hospitalized for burns.