ارزيابي خطر نشت گاز كلر در ايستگاههاي كلر زني سيستم آب آشاميدني شهر تهران با روش تجزيه تحليل درخت خطا

Evaluation of chorine leakage hazards in chlorination stations of Tehran water purification system by FTA technique

Objective: From the point of chemical safety, chlorine gas is one of the dangerous chemicals, which is mainly used in water treatment industry for production of drinking water. In Tehran metropolis, the chlorination stations are one of the most crisis focus, because of high number of chlorination stations, their dispersion in the city, population trachoma near these stations and their continuous 24 hr operation. In addition, there is insufficient information on its method of spreading compounded by lack of knowledge on how to confronting an accident involving its spreading by fire-fighting organizations. The aim of the present study was to assess the event probability of an accident over one year in Tehran chlorination stations. Subjects and Methods:Fault Tree Analysis Technique was used to recognize the most effective factor in assessment of chlorine gas release. Then, compound method and their relation in form of terminal event, intermediate event and "OR" & "AND" gate were allocated. According to qualitative and quantitative analysis of Fault Tree, the most important factor in such event was recognized. Probability in safety assessment and calculation of event rate during one year were estimated. Results: The most important factors in the probability of occurrence of an event were non- existing training courses for staff and managers, high work pressure, inexistence of codified guidelines and rules and also unsuitable design of stations. The collected data on the probability of chlorine gas release was 21 times/year. Conclusion: These results suggest that safety training courses for both staff and managers are urgently needed. Reformatory modification in staff shift work and in control team are also recommended.