Sixty years on: the price of assembling military gas masks in 1940

Between 1940 and 1944 military gas masks with filter pads containing 20% crocidolite were assembled in a Nottingham factory.

Records supplied by the late Professor Stephen Jones were of 1154 persons, mainly women, who had worked in the factory during this period; they included many deaths from mesothelioma. A systematic effort was therefore made to establish causes of death for the whole cohort.

Of 640 employees with full name and sex recorded, 567 (89%) were traced. Of these, 491 had died, including 65 from mesothelioma, though only 54 were certified as such. After exclusion of these 54, standardised mortality ratios were significantly raised for respiratory cancer (SMR 2.5) and carcinomatosis (SMR 3.2). The pattern of mortality in the remaining 514 employees without full identification was similar, but a low tracing rate (40%) did not justify their further analysis. The first death from mesothelioma was in 1963 (22 years after first exposure) and the last in 1994, whereas a further 5.0 cases would have been expected between 1996 and 2003 (p = 0.0065).

These findings in a cohort followed over 60 years after brief exposure to crocidolite confirm a high and specific risk of mesothelioma (28% peritoneal) and perhaps of lung cancer some 20-50 years later. The statistically significant absence of further mesothelioma cases during the past eight years suggests that crocidolite, though durable, is slowly removed.