ارزیابی ریسک نیمه کمی مواجهه بهداشتی با ترکیبات آلی فرار در جایگاههای توزیع سوخت بنزین شهر سبزوار

Introduction
Volatile organic compounds are air polluting agents that are in the form of volatile liquids or solids. These compounds containing organic carbon are produced through various processes and evaporate at a high speed. Benzene, toluene, ethylbenzene, xylene (BTEX) are volatile organic compounds that have similar physical and chemical properties and are more important among volatile organic compounds. These materials are one of the main components of gasoline and one of the main solvents used in industries. BTEX present in used gasoline enters the air of cities through the exhaust, engine of vehicles and also as a result of gasoline evaporation from oil product distribution points, and in this way, gas station employees are exposed to these compounds. The increase in the distribution of gasoline in gas stations in recent years has caused the employees of these stations to be exposed to gasoline compounds. In order to decide on the control measures and protection of employees against adverse effects caused by chemical substances, it is necessary to specifically evaluate the health risks caused by exposure to these substances. Risk assessment can be used as one of the effective tools in environmental and health assessment, and it is needed for different jobs. Due to the high exposure of people working in refueling stations to dangerous organic substances, this study aims to evaluate the health risk of occupational exposure to volatile organic compounds in gasoline, in the employees of gasoline fuel distribution stations in Sabzevar city, and in order to provide solutions was done.

Material and method
This cross-sectional study was conducted in 9 gasoline fuel distribution stations in Sabzevar city in the winter of 2014 and the spring of 2015. After determining the positions, the health risk assessment of the investigated compounds was carried out in the positions. For this purpose, the method presented in the Health, Safety, and Environment unit of the Ministry of Oil of Iran has been used. At first, a working group was formed consisting of supervisors of the sites under investigation, staff representatives and environmental pollution experts. In the next step, in order to analyze the work process, the employees were grouped according to their job duties. Then, according to the specificity of the investigated chemicals, BTEX in gasoline, the Hazard Rate (HR) of each of these compounds was determined. For this purpose, risk assessment was carried out in 3 steps: 1) determination of the Hazard Rate, 2) determination of the Exposure Rate (ER), and 3) determination of the Risk Level (RL). After identifying the chemicals in question, in this stage, the level of toxicity or risks caused by these substances was determined. Substances are classified into 5 levels of risk based on the toxic effects or harmful side effects of the chemical substance. According to the provided guide, the ER can be determined using the actual exposure level (pollutant measurement results) or using the exposure index (Exposure Index (EI)). Then the level of risk is obtained according to the degree of danger of the chemical substance (HR) and the degree of exposure (ER). Finally, the risk rating was determined in order to provide a control solution.

Results and duscussion
The results of the risk analysis and evaluation in all the studied sites showed that the highest risk score was assigned to benzene with a very high rank, ethyl benzene was ranked next, i.e. high, and two other compounds, toluene and xylene, had an average rank assigned to themselves. It is very important to control health risks from the stage of production, use and disposal of chemicals. In recent years, with the increasing urban population and the consequent increase in car production and refueling stations, gasoline consumption has increased and the risk of exposure to vapors caused by this chemical substance has increased. Health risk assessment of chemicals determines their adverse effects. During the investigations, it was determined that Beyhaq, Parsa, and Mehrizi locations have a higher risk score for benzene than other locations due to more traffic of heavy vehicles (Gasoline sales operator).
In the discharge operator's job, in Beyhaq and Al-Ahmed stations, due to the high amount of gasoline sales and the consequent increase in the amount of loading and unloading cargo per day (3 to 4 times a day), benzene has the highest risk score with a score of 4.36 and got a very high rating. In the above two positions in the discharge operator's job, ethylbenzene has a high risk rating and the two compounds xylene and toluene have a medium risk rating. In other locations such as Resalat, Parsa, Qarzi, Iran Zemin, Mianabadi and Mehrizi, benzene with a high risk rating had the highest amount of risk and ethylbenzene, toluene and xylene with a medium risk rating were ranked next. In all positions in administrative jobs, benzene with a risk score of 3.98 has the highest risk rating, i.e. a high rating, and the other three compounds all have a medium risk rating.

Conclusion
The increase in the distribution of gasoline in gas stations in recent years has caused the employees of these stations to be exposed to gasoline compounds. These people are in contact with a high level of BTEX compounds through inhalation and skin while refueling vehicles, emptying gasoline from the tanker into the tanks of the fuel distribution stations, cleaning the reservoirs and also opening the devices and equipments. The results showed that the personnel working in gasoline fuel distribution stations are exposed to volatile organic compounds in gasoline at high levels. In order to reduce the risk, it is necessary to take measures such as: controlling the risks at the source, replacing dangerous substances with safe or less dangerous substances, requiring annual and continuous environmental and biological measurement and monitoring in the locations, training to all employees regarding the dangers and health risks of exposure to chemicals in gasoline and its vapors for the use of personal protective equipment, medical examination and testing of sensitive employees such as respiratory and cardiac patients in order to work at the station, visit and control failure of nozzles and station equipments.