Abstract: Employees #1 through #4 and coworkers were using a liquid propane-powered forklift, borrowed by the employer from a neighboring company, to move 200 to 300 lb beef hindquarters. They were working in the hanging refrigerated cooler, which was an unvented enclosed area. The employees began to feel sick and experience symptoms consistent with carbon monoxide poisoning. Employees #1 through #4 were transported to Massachusetts General Hospital, where three of them spent four hours in a hyperbaric chamber. Seven coworkers were treated at nearby hospitals and one coworker was seen at a health clinic. The Chelsea (MA) Fire Department arrived 45 minutes after the first employees went for treatment; at that time, carbon monoxide levels ranged between 350 and 360 ppm in the work area.