Abstract: DURING THE EVENING OF OCTOBER 3, 1985, A CLEANING SERVICE BUFFERED THE FLOOR OF THE WORK AREA. THE PROPANE MOTOR OF THE BUFFER WAS NOT PROPERLY ADJUSTED AND WAS EXHAUSTING CARBON MONOXIDE INTO THE AIR. THE BUILDING WAS NEW AND VERY TIGHTLY SEALED. THE BUILDING USED A RECIRCULATING VENTILATION SYSTEM. ON THE MORNING OF OCTOBER 4, 1985, THE REGULAR EMPLOYEES RETURNED TO DUTY. BY 8 AM MANY EMPLOYEES WERE EXHIBITING SYMPTOMS OF CARBON MONOXIDE POISONING. BY 12:30 THE SYMPTOMS WERE SO SEVERE THAT 42 EMPLOYEES WERE SENT TO THE HOSPITAL. INTERVIEWS WITH THE EMPLOYEES REVEALED THAT MANY HAD CONTRACTED FLU OR COLDS PRIOR TO THE CARBON MONOXIDE EXPOSURE. BOTH THE CARBON MONOXIDE EXPOSURE AND THE RESPIRATORY INFECTIONS ARE CONSIDERED CAUSES OF THE SYMPTOMS.