Abstract: Between approximately 5:30 a.m. and 6:30 a.m. on August 21, 1992, Employees #1, #2, and #3 were performing their normal duties in the second floor office area of a plant (Employee #1 was cleaning, Employees #2 and #3 were discussing paperwork) when carbon monoxide poisoning led to evacuation of the building. Employee #2 observed Employee #1 collapsing. Employee #3 went to the aid of Employee #1. Employee #2, who was dizzy, attempted with difficulty to call rescue authorities. She eventually succeeded but then lost consciousness. Employee #3 called for plant evacuation and was assisted by Employees #4, #5, and #6 to evacuate stricken Employees #1 and #2. Emergency rescue equipment arrived at 7:22 a.m. and assisted with evacuation. Employees #1 through #6 were observed and treated by EMT personnel and taken to Denver General Hospital for further evaluation. There were no fatalities and no hospital admissions. Although the employer's boiler was suspected, no source of carbon monoxide was positively identified.