Carbon monoxide toxicity was apparently the key issue in the 1995 deaths of the firefighters, who were unable to escape from the interior of a burning dwelling. Two of the firefighters were believed to have removed or loosened their face pieces and made attempts to share the air that was available by "buddy breathing," or alternating the use of the breathing apparatus. All three of the firefighters were eventually rendered unconscious due to carbon monoxide inhalation or oxygen deficiency. One of the many unanswered questions in the investigation was how long the two firefighters practiced buddy breathing before becoming incapacitated. This required a determination of the concentration of carbon monoxide in the room where the firefighters were found. This was done with the use of the FDS, which is a computational fluid dynamics (CFD) fire model that uses large eddy simulation techniques to predict the thermal conditions that result from a compartment fire. The user specifies the dimensions and properties of the structure of interest, dividing it into small rectangular control volumes or computational cells. The model then computes the density, velocity, temperature, pressure, and species concentration of the gas in each cell based on the conservation laws of mass, momentum, and energy to model the movement of fire gases. The model also uses material properties of the furnishings, walls, floors, and ceilings to simulate fire growth and spread. The output of the FDS program consists of several data files, including visualization files and spreadsheets. Smokeview is a visualization program that displays the results of FDS computed data by animating time-dependent variables such as particle movement, temperature, heat flux, and specified concentrations. Using an equation that describes the relationship between blood carboxyhemoglobin, the concentration of carbon monoxide, and the volume of inspired air, the time of exposure was calculated. The model indicated that 27 minutes into the fire, the carbon monoxide concentration had already reached approximately 3600 ppm. At this concentration and a respiration of 70 L/min, an estimated 3 to 8 minutes of exposure would have been required to accumulate the concentration of carboxyhemoglobin measured on the firefighters at autopsy. 1 table, 1 figure, and 14 references