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 expos ure levels before and after the installation of vapour recovery facilities at 14 Service stations. Road tanker drivers are exposed when handling volat ile petrol liquid in bulk in the distribution chain. The drivers' exposure was studied during the unloading operation as the bulk petrol flowed into u nderground 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 in stalled for recycling vapours. Short-term measurements were carried out in the drivers' breathing zones by drawing polluted air through a charcoal tub e during unloading. The samples were analysed in the laboratory by gas chro matography for C3-C11 aliphatic hydrocarbons, tert-butyl methyl ether (MTBE ), tert-amyl methyl ether (MTAE), benzene, toluene and xylene. The road tan ker loads delivered consisted of oxygenated and reformulated petrol (E95 an d E98 brands), which contained on average 13% oxygenates. Before the instal lation 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 dr ivers' 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 vap our recovery. The differences between the aliphatic hydrocarbons and the MT BE exposure levels during the unloading of the road tankers without and wit h vapour recovery were statistically significant (p < 0.05).