Consequence Modeling of Chlorine Gas Leakage and Hazard Zone Determination in Ahvaz Water Treatment Plant No. 1 Using PHAST Software

Ahvaz Water Treatment Plant No. 1, with a capacity of over 140,000 cubic meters per day, supplies approximately 15 to 20 percent of the drinking water for the metropolis of Ahvaz. The disinfection process in this plant is carried out using one-ton pressurized chlorine gas cylinders. Chlorine, as an oxidizing and highly toxic substance, is considered one of the most significant potential hazards in this facility. Given that the distance from the plant to the nearest residential areas is less than 400 meters, a precise assessment of the consequences of potential leaks is of great necessity. In this study, the consequences of various chlorine gas leak scenarios at Ahvaz Water Treatment Plant No. 1 were modeled using PHAST software version 8.4. A total of 12 scenarios were considered as the basis for the assessment. The results indicated that increasing the leak diameter from 1 to 10 mm, along with changing the atmospheric stability class from the most unstable (Class A) to the most stable (Class F), increases the maximum impact radius at the AEGL-2 and IDLH levels by between 5 and 10 times. Furthermore, increasing the leak diameter increased the LC₅₀ and Probit values corresponding to 5 (50% mortality) by approximately 4 times. In the worst-case scenario, the effective distances to the AEGL-2 and IDLH thresholds were estimated as 2,200 and 1,600 meters from the release source, respectively.