A Simultaneous Job- and Task-Based Exposure Evaluation of Petroleum Tanker Drivers to Benzene and Total Hydrocarbons

Abstract

A simultaneous job- and task-based exposure study was conducted for tanker drivers delivering petroleum products from several bulk terminals and an agency to retail outlets. Full-shift (job-based) samples and job component tasks samples were collected simultaneously. The tasks sampled included loading, unloading, and travel. Three hundred sixty-six personal charcoal tube samples were collected. Full-shift visual observations of work practices and real-time monitoring using a datalogging hydrocarbon analyzer were also conducted. Multiple measurements per worker were made, which permitted an assessment of sampling variability within and between workers. The highest exposures for drivers occurred during unloading at the agency. The mean benzene exposure for agency drivers was 0.88 ppm for full-shift time-weighted average, 2.86 ppm for unloading, and 0.54 ppm for loading. For bulk terminal drivers, the mean benzene level without vapor control was 0.12 ppm for time weighted average, 0.24 ppm for unloading, and 0.33 ppm for loading. The time-weighted average exposure of the agency and bulk terminal drivers based on the data collected and the lognormal model can be expected to exceed threshold limit value-time weighted average of 0.5 ppm for benzene about 70 and 2% of the time, respectively. Agency drivers' unloading and loading tasks accounted for approximately 30% and 7% of the total time, and 95% and 4% of total exposure, respectively. For the bulk terminal drivers, mean unloading and loading tasks constituted 24% and 12% of the total time, and 68% and 19% of the total exposure, respectively. Travel activity accounted for an average of 63% of the total time for agency and 64% for bulk terminal drivers, but only contributed < 1 and 13% of the total exposure, respectively. The actual job-based time-weighted average concentration and the calculated time-weighted average derived from the time-weighted summation of the components tasks are in very good agreement. Within-worker variability was generally higher than between-worker variability. Exposure control strategies are required primarily for unloading at the agencies. Vapor control technology at the terminal effectively reduces exposure (by almost 50%) and fugitive emissions.

Keywords:

• agency
• benzene
• between- and within-worker variability
• bulk terminal
• gasoline
• vapor control

ACKNOWLEDGMENT

The authors are grateful to the Canadian Petroleum Products Institute for their financial support. We thank the management and employees of the companies who participated in this study for their active support. Without their cooperation, this study could not have been possible. Finally, the authors thank Colleen Stevenson, Linda Spruce, and Karen des Tombe for their help.

Notes

^A n = number of samples.

^B k = number of workers.

^C Min = minimum.

^D max = maximum.

^E AM = Arithmetic mean.

^F GM = Geometric mean.

^G GSD = geometric standard deviation.

^H m = number of agencies/bulk terminals.

^I No vapor controls were used at the agency operation or during travel.

^J NVC = no vapor control.

^K VC = vapor control.

^L Includes some with partial vapor control.

^A n = Number of samples.

^B k = number of workers.

^C GSD _B = between-worker variability.

^D GSD _W = within-worker variability.

^E THC as gasoline.

^F m = number of agencies/bulk terminals.

^G NVC = no vapor control.

^H VC = vapor control.

^A NVC = no vapor control.

^B VC = vapor control.

^C df = degrees of freedom.

^D β = estimated coefficient.

^E (se) = standard error of the estimate.

^F e^β= estimated multiplier.

^A β = estimated coefficient.

^B (se) = standard error of the estimate.

^C e^β = estimated multiplier.