Abstract: Between 6:00 a.m. and 8:00 a.m. on June 21, 2001, Employees #1, #2, #3, #4, and #5 arrived for work at Aventis Bio-Services, Inc., and noticed an intense propane smell. Prior to their arrival at work, a propane buffer had been utilized. These five employees and other coworkers, along with customers of the clinic, began presenting symptoms of carbon monoxide poisoning (i.e., nausea, headache, and dizziness) and complained of the gaseous odor. At 9:00 a.m., the employees' symptoms persisted, prompting a call to the center manager. The company evacuated the facility and opened the front doors for ventilation. Four employees were transferred by ambulance to the emergency room, where testing revealed elevated carboxyhemoglobin levels. Three additional employees opted to return home.