Mortality patterns among civilian workers in Royal Navy Dockyards

This is a study of asbestos related disease in civilian workers at 3 Royal Naval Dockyards, namely: Devonport, Chatham and Portsmouth. Past work in these dockyards, along with Rosyth in Scotland (undertaken by the Institute of Naval Medicine and the Medical Research Council), has shown that just under 5% of this workforce might be expected to have radiographic abnormalities due to asbestos exposure. In the early 1970s workers in all 4 of these dockyards were invited to participate in health surveys, in which chest x-rays were performed and a health/employment history questionnaire given. This work is an exact 17 year follow-up of these health surveys, analysing cause specific mortality its time trends and their correlates. The working population of the 3 dockyards, including female industrial workers and ‘outstation’ male workers was 32,931. However, excluding female workers and absolute non-responders reduced this to 28,265 male workers. The trace rate of this population, over the 17 years, was 97.3% (Rosyth with a rate of less than 70% was excluded from this analysis), 18% of the population traced were found to be dead. The mortality patterns of this cohort were inspected on a yearly basis by the use of a regionally adjusted SMR analysis. Expected rates were calculated, using the OPCS historic mortality data files, to provide a reference set of background mortality levels. The striking result from this study is one of no excess risk due to lung cancer at the three dockyards, producing SMRs of: 99 (95%CI: 87-122) at Devonport, 85 (95%CI: 70-101) at Chatham, and 94 (95%CI: 81-106) at Portsmouth [X2=1.8, P>0.1]. However, an excessive risk was seen for pleural mesothelioma that produced SMRs of: 1983 (95%CI: 1505-2461) at Devonport, 1638(95%CI: 1049- 2437) at Chatham, and 1042 (95%CI: 693-1506) at Portsmouth [X2 = 8.4, P< 0.025]. Excesses were also seen for peritoneal mesothelioma and asbestosis. No obvious relationships were seen when analysing lung cancer mortality by employment and asbestos exposure variables. A dose-response of lung cancer mortality to smoking habit was the only clear relationship found. Log-linear modelling supported the SMR findings of no overall excess or deficiency of lung cancer mortality compared to an excess of mesothelioma deaths. These results and their significance are discussed.