Comparison of tanker drivers' occupational exposures before and after the installation of a vapour recovery system.

The purpose of this study was to compare tanker drivers' occupational exposure level before and after the installation of vapour recovery facilities at 14 service stations. Road tanker drivers are exposed when handling volatile petrol liquid in bulk in the distribution chain. The drivers' exposure was studied during the unloading operation as the bulk petrol flowed into underground storage tanks, displacing vapours in the tank space and causing emission to the environment and the drivers' work area. The exposures were measured again when the dual point Stage I vapour recovery systems were installed for recycling vapours. Short-term measurements were carried out in the drivers' breathing zones by drawing polluted air through a charcoal tube during unloading. The samples were analysed in the laboratory by gas chromatography for C3-C11 aliphatic hydrocarbons, tert-butyl methyl ether (MTBE), tert-amyl methyl ether (MTAE), benzene, toluene and xylene. The road tanker loads delivered consisted of oxygenated and reformulated petrol (E95 and E98 brands), which contained on average 13% oxygenates. Before the installation of the vapour recovery system, the geometric mean (GM) concentration of aliphatic hydrocarbons was 65 mg m-3 (range 6-645 mg m-3) in the drivers' breathing zones. After the installation at the same service stations, the corresponding exposure level was 8.3 mg m-3 (range < 1-79 mg m-3). The GM of the MTBE concentrations was 8.6 mg m-3 (range 1-67 mg m-3) without vapour recovery and 1.5 mg m-3 (range < 0.1-10 mg m-3) with vapour recovery. The differences between the aliphatic hydrocarbons and the MTBE exposure levels during the unloading of the road tankers without and with vapour recovery were statistically significant (p < 0.05).