Abstract: On April 1, 2002, Employee #1 and Employee #2 were monitoring the equipment for a water treatment system, which consists of management of sodium bisulfate and sodium hypochlorite levels. These two different chemicals are kept in yellow 120-liter drums, which are located side by side and labeled on top in block lettering less than an inch high. During the morning inspection, it was revealed that the bisulfate drum was low and needed to be filled. Either Employee #1 or #2 inadvertently retrieved a supply (55 gallon, blue) drum of sodium hypochlorite, labeled with the manufacturer's label, as well as stenciled BISULFITE or BLEACH in letters slightly less than an inch high. Approximately 20 liters of the sodium hypochlorite was pumped into the yellow sodium bisulfate drum. The yellow bisulfate drum violently ruptured, spraying the two employees engaged in the filling operation. Three coworkers immediately assisted with evacuation and decontamination of Employee #1 and Employee #2 prior to emergency services arriving. Employee #1 and Employee #2 were hospitalized with very severe chemical burns and respiratory injuries; the three others were treated for respiratory difficulties and released.