Benzene exposures during tank washing activities on crude oil tankers

Personal benzene exposure data during tank washing aboard crude oil tankers are presented. The data are from 4 monitoring surveys conducted by a tanker ship company in the 1990s. Among 59 partial-shift samples for personnel on deck during tank washing, the sample mean was 0.49 ppm and 44% of the corresponding minimum 8-h time-weighted average (TWA) benzene exposure values exceeded 0.2 ppm (the European Union 8-h TWA benzene limit). Among 13 full-shift samples for personnel on deck, the equivalent 8-h TWA benzene exposure values had a sample mean of 0.44 ppm, and a parametrically estimated 85% exceeded 0.2 ppm. Among seven 15-min TWA benzene exposure values for personnel on deck who lowered portable wash machines into tanks and hoisted them out of tanks, the sample mean was 6.48 ppm and a parametrically estimated 52% exceeded 5 ppm (the US Occupational Safety and Health Administration 15-min TWA benzene limit). Among 13 partial-shift samples for personnel mucking inside a tank, the sample mean was 13.5 ppm, 100% of the minimum 8-h TWA benzene exposure levels exceeded 0.2 ppm, 92% exceeded 1 ppm (the U.S. 8-h TWA benzene limit), and 77% exceeded 5 ppm. Among 5 partial-shift samples for personnel assisting mucking from the deck, the sample mean was 1.03 ppm, and 60% of the minimum 8-h TWA benzene exposure levels exceeded 0.2 ppm. Because at present mucking may be seldom performed, and because portable wash machine use has substantially decreased, the associated exposures described here may be primarily of interest for epidemiological studies and questions of causation in the context of clinical evaluation.