Abstract: Employee #1, a grocery store employee, was working at the same time that construction workers were in the store operating a concrete saw. The saw was powered by a generator, which had originally been located outside but which was brought inside after complaints about noise. The generator had been on for between two and three hours when Employee #1 fell down, unconscious. It was determined that gasoline exhaust from the generator had released carbon monoxide fumes into the store, and that Employee #1 was suffering from carbon monoxide poisoning. He and twelve coworkers were evacuated from the store, taken to local hospitals, and eventually treated in hyperbaric chambers at UCSD Medical Center. A treating physician's statement indicates that carboxyhemoglobin levels in the workers ranged from 17 to 26 percent, and that Employee #1's levels may have exceeded 36 percent. No ventilation duct had been provided to pipe the exhaust gases outside of the store during the cutting work, and no monitoring was done by the employer or by the contractor. The employer did not evaluate the hazard of gasoline engine exhaust to its employees but trusted the contractor to provide adequate ventilation for its equipment. The contractor had exacerbated the situation by placing the generator in the vicinity of an air compressor intake that was being used to power a jackhammer. The intake distributed the exhaust fumes to other areas of the store through the air lines of the compressor. Administrative controls, such as cordoning off the area or keeping workers out of the store while the saw cutter was in use, were not used.