In July 2006, NIOSH received a confidential HHE request from employees at Kaleida Health-Buffalo General Hospital in Buffalo, New York. The HHE request stated that inadequate ventilation was provided in the A2 GI Lab Steris Room where five employees clean and sterilize endoscopes with Klenzyme Enzymatic Cleaner and Steris 20 Sterilant Concentrate. Health problems identified in the request were headache, shortness of breath, eye irritation, and diminished sense of smell. On December 18-19, 2006, we conducted a site visit that included an opening conference, a walk-through of the A2 GI Lab Steris Room, air sampling for peracetic and acetic acids, measurements of temperature and RH, smoke tube visualization of airflow, and confidential informal interviews with several employees. Air samples did not contain detectable concentrations of acetic acid. Sampling results and our onsite observations indicate very little, if any, airborne exposure to peracetic acid sterilant on the sampling date. The temperature was 74 degrees F to 76 degrees F, and the RH was 17% to 20%. Smoke tube visualization of airflow at the ceiling-mounted ventilation supply diffusers and return grilles in the Steris room indicated that the HVAC system provided insufficient airflow. Ventilation in the Steris room appeared to be inadequate for providing reliable odor control and maintaining the work environment within an acceptable range of temperature and RH. Employees reported periodic headaches and burning eyes that were more noticeable when SS1 processors malfunctioned and leaked. Poor ventilation and high environmental temperatures were noted by workers. Although gloves, sleeves and aprons are provided, some workers reported not using all available PPE due to high environmental temperatures. Two workers reported prior chemical burns from occupational exposure to Steris 20 Sterilant Concentrate. Several workers reported that they had not received formal chemical hazard communication training for Steris room operations. A review of FDA CDRH data files indicated that occupational exposure to peracetic acid sterilant should be unlikely when SS1 processors are maintained and operated properly and when technicians follow the manufacturer's operating procedures. However, processor malfunctions and improper handling and disposal of Steris 20 Sterilant Concentrate containers can result in dermal or inhalation exposures. Appropriate employee training, use of adequate PPE, and routine maintenance of processors should help reduce the likelihood of worker exposures, as well as the risk of employee illness or injury if a spill or leak does occur.