TODAY NATIONS HAVE LEGISLATED SEVERE LAWS FOR PERMISSIBLE LIMITS OF AIR POLLUTANTS FROM INDUSTRIAL UNITS. HYDROGEN CYANIDE, KNOWN AS ONE OF THE MOST TOXIC GASES, IS THE EFFLUENT GAS FROM HEAT TREATMENT OF POLYMERS CONTAINING NITRILE GROUPS SUCH AS POLYACRYLONITRILE (PAN). IN THIS WORK, THE POLLUTANTS DUE TO POLYACRYLONITRILE PYROLYSIS IS PRESENTED AND CONTAMINATION EXTENT CONCERNING HYDROGEN CYANIDE FROM carbon fiber FURNACES IN "IRANIAN RESEARCH AND DEVELOPMENT CENTER FOR ADVANCED fiberS" IS EVALUATED. HYDROGEN CYANIDE RELEASE WERE MESURED AT THREE DIFFERENT SECTION OF PAN carbon fiber PRODUCTION UNITS, OXIDATION FURNACE, HIGH TEMPERATURE FURNACE, AND BEFORE ENTERING GAS PURIFICATION UNIT PRODUCING 150 AND 196 carbon fiberS. THE HIGHEST CYANIDE CONCENTRATION WAS OBSERVED IN HT FURNACE AS EXPECTED AND IN THE CASE OF 196 carbon fiber PRODUCTION THE CYANIDE FORMATION WAS DOUBLED.