Abstract: At 7:15 a.m. on March 19, 1997, a general contractor began jackhammering while a subcontractor started to cut concrete using a 35 hp Meco gasoline-powered generator to power the concrete saw. The generator was in the mechanical lab area and ran for 45 minutes. Employee #1, age 20, and three coworkers were exposed to carbon monoxide from the generator. Employee #1 and one coworker were transported by ambulance to Western Medical Center; the two other coworkers were driven to the hospital by the superintendent. Employee #1's carboxyhemoglobin level (COHB) was 23.8; those of the three coworkers were 27.3, 21.6, and 18.8. All four workers were treated in a hyperbaric chamber and released in satisfactory condition after 4 to 6 hours at the hospital. The employers were cited for serious violations of T8CCR 1528(b), for failing to protect its workers from exposure to harmful substances (carbon monoxide); and of T8CCR 1533(a), for operating equipment driven by an internal combustion engine inside the mechanical lab area without adequate methods of control.