Background and aims:Toxic chemical release from process installation is one of the main hazards in chemical industries which can endanger the health of employees and public in the neighbours of industry in case of occurring chemical release accident. The aim of this study was determining hazard distance of toxic chemical release in one of petrochemical complex for its applicability in emergency response planning.Methods:Different possible scenarios for toxic chemical release was considered and the worse case scenarios including process vessels rupture was selected for hazard distance study by aid of Dow Chemical Exposure Index (CEI).Results:Among studied chemical tanks including Chlorine, Phenol, Epichlorohydrin (EPI), Chlorobenzene, Toluene, hydrogen chloride, the highest Chemical Exposure Index (CEI) and hazard distance was for Chlorine with CEI of 340 and hazard distance for ERPG 2 and ERPG 3 concentration were 3399 and 1339 respectively.Conclusion:Chemical Exposure Index (CEI) can be used for determining hazard distance of a chemical release accident. Hazard distance data can be used in process installation layout and emergency response planning.