Abstract: On December 13, 2007, Employee #1, a 45-year-old pulmonary function technician, was assigned to conduct a blood gas analysis test for an open heart surgery case in an OR on the fourth floor of USC University Hospital, where she had been working for about two years. Employee #1, who was trained in general safety, noticed a bleach-type smell, but continued working in the OR. Minutes later, she started to cough and decided to leave the area, but she got a call to return to the OR and complete the blood gas analysis test. About 10 to 20 minutes later, Employee #1's supervisor instructed her to leave the room. When she reached the second floor, her cough became more frequent. After the accident, Employee #1 was taken by ambulance to LA County USC Medical Center, and eight hours later, she was transported to USC University Hospital, where she spent four days in the ICU because of respiratory distress. At the time of the accident, Employee #1 did not know what caused the uncontrollable cough that preceded respiratory distress. It was later determined that Employee #2 used two different cleaning products when cleaning the HVAC system that serviced the fourth floor. Clorox Bleach was used to clean the drain pans, and Acti-Klean was used to clean the coils. The two cleaners were mixed, creating gases or toxic fumes. Based on the MSDSs, the two cleaning products, when mixed, can create a chlorinated gas or toxic fume, which led to the chemical exposure of Employee #1, in addition to an unspecified number of employees working in the surrounding area.