Abstract: On July 15, 1990, Employee #1 and a crew, of Songer Corp., were welding inside a vessel boiler doing repair work. Air was being supplied by an air horn that was hooked up to the Great Lakes Steel air supply system. This system was used for cooling and ventilation. At 2:30 p.m., Employee #1 and the crew exited for a coffee break. At this time the air horn was removed from the manway opening and placed inside the vessel. Employee #1 returned to the vessel and, upon entering, was overcome by the lack of oxygen; nitrogen was induced into the compressed air line. Employee #1 died. This investigation was conducted jointly with the local health department. The employer was issued a serious citation.