Abstract: At approximately 11:35 a.m. on May 10, 2007, Employee #1, the owner of a home repair company, and two employees, were working at a residential location framing and finishing the basement. The job included cutting a hole in the concrete wall to install a window. Employee #1 was doing the cutting using a 2-cycle, oil and gas, STIHL Model Number TS 400 cut-off saw. Employee #1 was wearing a 3M, half face, elastomeric respirator equipped with organic vapor cartridges. In an attempt to contain and ventilate the exhaust from the cut off saw to the outside, the employees had constructed a plastic tent around the area to be cut. The containment structure measured approximately 66 in. long by 52 in. wide and was 84 in. high. The employees stated that during the operation, it was sealed pretty tight. At the top right hand corner (facing the wall), a 2-in. diameter hose was inserted into the structure. This hose was attached to a 12-gallon, 4.25-horsepower, Rigid wet and dry vacuum to remove the exhaust from the containment area. A second hose was also attached to the blowing side of the vacuum, with the other end of the hose placed outside of the basement through an existing window to carry the exhaust to the outside. According tone coworker, Employee #1 had been operating the concrete saw inside the containment area off and on for about 2 hours. The coworker stated that Employee #1 had stopped cutting a few times and walked outside for fresh air. The coworker stated that the last time Employee #1 exited the basement, he called for the coworker. The coworker went outside and could see that Employee #1 was not doing very well. Employee #1 passed out for approximately a minute before regaining consciousness and vomiting. Emergency services responded and transported Employee #1 to the hospital where he was treated in an oxygen chamber and released from the hospital the same day. Emergency services staff obtained readings of approximately 80 parts-per-million of carbon monoxide in the containment area.