Abstract: On January 6, 1995, three contractor employees were removing an old waste heat duct from the gas-fired boiler room at a corn processing plant. At the time, four administrative employees were working in or near the boiler room. The contractor employees began to suffer symptoms consistent with carbon monoxide poisoning; all three had elevated levels of carboxyhemoglobin and were hospitalized. As a precaution, the four administrative employees were also taken to the hospital, where they treated and released. The source of the carbon monoxide was traced to the improperly tuned and leaking boilers.