Abstract: On December 9, 1988, Employees #1 through #5 were working at the Stapleton International Airport boiler building asbestos abatement project, which had been contracted to Mac-Bestos, Inc. They were wearing supplied air respirators. A gasoline-powered air compressor was located outside the building and pumped air to an Air-Burst Jr. breathing system, which directed the air to the respirators. The breathing air system, when operated correctly, sounds an alarm if the air compressor is sending air that is unfit for breathing. The system also has a back up which then sends breathable air to the respirators. At approximately 11:00 a.m., Employees #1 through #5 were overexposed to carbon monoxide, which was pumped to the Air-Burst Jr. and then sent to the respirators without sounding an alarm. All five employees had been working for less than 15 minutes. At 11:15 a.m., Employee #1 passed out and had to be carried from the abatement area. Emergency help arrived at 11:30 a.m. and administered oxygen to all five employees. They were transported to the hospital for blood tests and were treated in a hyperbaric chamber. Their carboxyhemoglobin levels ranged from 16 to 24 percent.