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Exposure Assessment for Toxic Vapors During Underground Storage Tank Inspections


The purpose of this project was determining the exposure of toxic vapors, particularly benzene, toluene, ethylbenzene and xylene (BTEX), to workers during an underground storage tanks (UST) inspection process. BTEX are a group of hydrocarbons that are commonly found as volatile organic compounds (VOCs) in gasoline products. Thousands of other VOCs can also be found in gasoline, some that have been identified and others that have not. For this project, a total of 8 different fillingstations were examined during a UST inspection with the help of a local regulatory agency. The project was conducted during the months of January to April 2017. The exposure assessment was divided into 4 phases(laboratory pre-calibrations, preliminary, secondary and personal sampling) to assess whether high air concentrations of VOCs and BTEX were present at the sites. A Photoionization Detector (ppbRAE 7240) was used to measure total VOC levels. A portable Gas Chromatography (GC) (PetroPRO) was used to measure the levels of BTEX. Integrated personal breathing zone sampling was also done at four sites with time ranges of 60-99 minutes. Personal samples were analyzed by GCMS after desorption of the charcoal tube with carbon disulfide.

VOC levels were at much higher concentrations when compared to the BTEX levels at concentrations ranging from 1.0ppm to 200ppm. BTEX concentrations levels decreased over time at constant cool temperatures and ranged from 118 to 340, 151 to 483, 276 to 926, and 249 to 869 ppb for BTEX, respectively. It was also observed that with higher increasing ambient temperatures, concentrations increased over time from 111 to 769, 81 to 504, 75 to 503, and 68 to 406ppb for BTEX, respectively. BTEX concentrations were overall below OSHA’s PELs and STELs, and NIOSH STELs. For one particular site, concentrations of benzene did exceed NIOSH RELs of 0.1 ppm (100ppb) and was above OSHA’s Action Level (AL) at 0.5 ppm (500ppb).

Overall, BTEX concentrations decreased over time with cooler temperatures and increased with warmer temperatures. VOCs were significantly high based on location and concentrations levels changed based on the time of the day related to temperatures. Turbine sumps showed the highest concentrations for VOCs and BTEX when compared to fillings sumps and dispenser sumps. Personal samples results were basically inconclusive because the samples were not analyzed until 6 months after sampling. Also, exposure assessment was not done for a total 8-hour exposure as required to compare with Cal/OSHA regulations and NIOSH guidelines. Similar concentrations were found for benzene and xylene (benzene being the highest concentration and xylenes being the lowest) as Site 4. All data were lower than 0.1 Cal/OSHA PELs, with the highest concentrations being 40.8 ppb for Site 5 and the lowest at 0.5 ppb for Site 6.In general, exposure levels to BTEX were not of immediate concern but it is still recommended for workers to take preventative measures to reduce exposures.

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