Abstract: At approximately 5:55 a.m. on June 15, 1990, Employee #1 was exposed to carbon monoxide while alone in the break room on the second floor of the steam generation building at the Weyerhaeuser Paper Company. Employees #2 and #3 were hospitalized and several other individuals were medically evaluated and released as a result of carbon monoxide poisoning during the rescue of Employee #1. Employee #1 died shortly after his arrival at the hospital. Blood analysis from the autopsy report indicated a carboxyhemoglobin concentration in excess of 70 percent saturation. Employees #2 and #3, as well as some of the medically evaluated individuals, had suggestive evidence of carbon monoxide exposure; however, no carbon monoxide blood analysis was conducted on these individuals on the day of the accident. The cause of the exposure is unknown; however, the most likely source would be the ash line that runs vertically through the break room. This line carries ash and flue gases generated from the combustion of wood bark, oil, and coal in boiler #1. This exposure could have been caused by a stock puff (explosion) that would cause the pressure in the line to briefly go positive. The condition will be abated by relocating the break room to avoid close contact with process lines.