Abstract: On March 21, 2014, Employees #1, #2, #3, and #4, a supervisory mason and members of his crew of masons, all employed by a tile and marble construction contractor, were engaged in removing the epoxy floor system from the kitchen area of a county jail. They were using an EDCO SS-20 propane-powered concrete saw to cut a 60-foot by 40-foot grid pattern into the floor to expedite its removal. The four employees were located at different locations around the saw and performing various duties, including operating the saw, handling hoses, and using shop vacuums to clean up the floor area. The work had been in progress for an estimated 45 minutes when one of the employees, located in direct proximity to the saw's exhaust fumes, began to experience symptoms of nausea, lightheadedness, and disorientation. The employee was removed from the work area to fresh air. A fellow crew member then communicated to the other employees that their colleague was experiencing these symptoms. The three other employees in the work area stated that they were experiencing lightheadedness, also. Emergency services were called. Two of the four sickened employees were evaluated by an emergency medical responder and declined further treatment. The other two employees were transported to Carolina Medical Center, evaluated, and released. These two employees had carboxyhemoglobin levels of 15.9 and 9.7. This event was investigated by North Carolina OSHA. A Compliance Safety and Health Officer (CSHO) conducting the investigation used the Coburn equation to calculate a theoretical carbon monoxide exposure based on 85 minutes and 63 minutes of exposure, respectively. The CSHO calculated that one of the two evaluated employees had an exposure of 56.67 ppm, and the other evaluated employee had an exposure of 35.57 ppm. These exposures were calculated as 8-hour time weighted averages to determine an overexposure to the OSHA PEL of 50 ppm.