Background and aims: Process industries are known to be hazardous industries. Chemical Industrial process involves several processes such as drilling and production, storage, transportation, and refining. These activities are different in nature. Also, they are different in job Risks. One of the main and dangerous sections of the process is oil reservoir. Therefore, this study aimed to identify factors affecting of the risk of chemical release staring at floating roof storage tanks in oil and gas industry.

 Methods: In this study, fuzzy fault tree analysis (FFTA) to identify and evaluate the risk of the release floating roof storage tanks used in oil refineries. Collect information and identify risks and possible events were used through observation, interviews, information of the process and materials. To calculate the probability of intermediate and main event of Boolean math notation was used. Isolation of the final events was unknown with the known repetition rate and the rate of failure.

Results: The results showed that the most likely cause of liquid chemical release oil from floating roof tanks was "tank fitting and overflow leakage of oil". Possibility of a chemical release liquid petroleum refinery industry 0.251 floating roof tank was calculated that this level is very high risk for staff and equipment for refineries.

Conclusion: according to the results, it was determined that according to determining critical MCs and the calculation of the importance of adopting remove control the way in reducing the likelihood of chemical release repository to be effective.