Abstract: Employees #1 and #2, both mechanics, were sent to the third level of the #2 Bethcon Line Selas furnace to remove a defective centrifugal blower that had stopped supplying an air curtain to the tinning process. As the mechanics loosened the bolts attaching the duct work to the blower, they detected the odor of flue gas. They immediately left the area, secured an MSA Minico IV carbon monoxide detector, returned to the blower, and measured carbon monoxide in excess of l,000 ppm at the blower intake. They left the area and reported the incident to a foreman. Employees #1 and #2 then began to feel ill and were transported to the hospital for observation.