Abstract: At approximately 9:45 a.m. on April 1, 1992, Employee #1, of All Chemical Disposal, Inc., and a coworker were at an outdoor hazardous waste storage bin at the site of a General Circuits facility in Menlo Park, CA. At the direction of Tanklage Construction Co., Inc., they were adding various chemicals into a bin that already contained hazardous waste. A chemical reaction and fire occurred. Both employees were wearing protective equipment, including respirators. Employee #1 left the area and went into an office to call for emergency assistance. He suffered exposure to chemical vapors and smoke when he removed his respirator to place the telephone call. He also experienced tightness in his chest and blurred vision. A characterization of the hazardous materials being bulked had not been performed; therefore, compatibility of the chemicals was not known.