Abstract: Employee #1, a maintenance mechanic in a TSD facility, was in the unloading area of the facility. Employee #1 was pumping hazardous acid waste drums into a holding tank using a hose attached to a tube, called a "stinger." In this procedure, the waste remaining in the drum is pumped down to the bottom 1 or 2 inches. The drum is then filled partially with water, and its contents are tipped into a containment pan. The drums are then rinsed several times into the pan. According to Employee #1, he pumped and rinsed 15 to 20 55-gallon drums and then pulled out three 30-gallon plastic drums. After he pumped out the first 30-gallon drum, he poured the rinse into the containment pan. A reaction occurred in the pan. Employee #1 started choking and went to the hospital, but fully recovered. (Employee #1 has a history of asthma.) Since hazardous waste labels were removed prior to dumping and rinsing, it is not certain what acids reacted. Two of the 30-gallon drums may have contained a sulfuric acid solution. A respirator was not worn because the drums were not labeled "fuming." Due to this accident, the employer established written drum-rinsing procedures to ensure that potentially hazardous material is removed from the containment pan before more waste is added.