Abstract: At approximately 9:00 p.m. on February 10, 2008, Quality Assurance Laboratory (QA Lab) employees noticed an odor and a haze in the lab. The QA Lab was located on the second story of the Corn Plant approximately midway between the Mill (north) and the Refinery (south) and adjacent to the Gluten Filter (East). An enclosed area housed the QA Lab, offices serving the Corn Plant, men's and women's locker rooms, Corn Plant East Conference Room and the Gluten Filter Control Room. This enclosed area was supplied by a single air handling system, a ProMark Associates, Inc., Air Conditioner/Scrubber, Model Number BFS4000-A/C-4 and Serial Number BFS4000-A/C-H-002. The unit provided heated air, which was first filtered through a carbon bed. At approximately 9:30 p.m., Employee #1 radioed Employee #2, who was the Plant General Foreman, and requested that he investigate the odor and haze. Within minutes, Employee #3 lost consciousness and fell to the ground in the QA Lab. Employee #1 saw the fall and again radioed Employee #2 for assistance and also requested a first aid responder. Employee# 4, a first aid responder, went to the QA Lab. He also lost consciousness, slumping to the ground approximately three minutes after his arrival in the lab. Another coworker who had a confined space meter told the employees in the lab that the carbon monoxide (CO) levels were high. At 9:44 p. m., the coworkers telephoned security and requested an ambulance, and then pulled Employees # 3 and #4 from the QA Lab. The Plant alarm began to sound at 9:55 p.m. This alarm signaled all employees to assemble in their respective control rooms for further instruction. Supervisors in the area began to report to their respective control rooms to take head counts and evacuate employees. At approximately 10:10 pm the Decatur Ambulance Service arrived and removed Employees #3 and #4. Employee #2 announced the area outside the lab contained an atmosphere of 200 ppm CO. Employees #3 and #4 were transported to Park Ridge for hyperbaric treatment. Both fully recovered and were released the next morning. At approximately 10:12 pm, Decatur Fire Department (FD) and Hazardous Materials Team arrived on the scene. From the Plant, another coworker radioed that Employee #5 and Employee #6, the Lab Supervisor, were down in the Gluten Filter Control Room. Employee #2, who had left the building, told the Decatur FD that employees were down and how to locate them. The FD suited up and entered the building. Their three gas meter "limited out" for CO on initial entry. The FD removed Employee #5 and #6. They were transported to Decatur Memorial Hospital Emergency Room, where they were both pronounced dead at approximately 11:10 pm. Employee #5 died from carbon monoxide poisoning. Employee #6 died from cardiac arrest brought on by carbon monoxide exposure. The Decatur FD determined that the air handling system in the roof, supplying the Lab area, was smoldering. The FD believed the carbon monoxide was from the smoldering carbon bed in the air handling system. The FD cut power to the system at the disconnect box. The FD opened doors to the enclosed area to ventilate and ensure that the air handling unit did not continue to burn. The FD remained in the area until CO levels were approximately 20 ppm. At that time, the FD turned the building over to the company. Two employees were treated for asphyxiation and released; two died and one was uninjured.