The smoke exposure hazards during combustion of carbon and nitrogen-containing fibers were evaluated in guinea pigs intoxicated by gradual exposure to HCN and CO neo-formed from foam rubber, wool and PAN (Polyacrylonitrile). The most prominent result of our study was that the neo-formation of HCN from 1 g of PAN was 1500 ppm, much higher than from foam rubber and wool because of the presence of many -CN groups in the polymer chemical structure. This concentration of HCN is estimated to be lethal. Extrapolating this data, a lethal concentration of HCN could be obtained by burning 2 kg of PAN in an average sized living room. The above-mentioned 1 g of PAN was burned in a 15.6-liter combustion chamber.