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

Our plain-English summary of Sixty years on: the price of assembling military gas masks in 1940, by J.C. McDonald, J.M. Harris, G. Berry (Occupational and Environmental Medicine, 2006).

The study

• Authors: J.C. McDonald, J.M. Harris, G. Berry
• Journal: Occupational and Environmental Medicine
• Published: 2006;63(12):852-5
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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

Methods: 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.

Results: 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).

Conclusion: 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.

In plain English

This report examined deaths among 1154 workers, about 93% of them women, recorded as having assembled military gas masks at a Nottingham factory between 1940 and 1944. The filter pads contained 20% crocidolite (blue asbestos). Of 640 workers with full name and sex recorded, 567 (89%) were traced through 2002, and 491 had died. In all, 65 deaths were attributed to mesothelioma, though only 54 were certified as such; 47 were pleural and 18 (28%) peritoneal. Among the fully recorded workers, excluding the 54 certified mesothelioma deaths, the standardised mortality ratio was 2.5 (95% CI 1.7 to 3.5) for respiratory cancer and 3.2 (95% CI 1.8 to 5.4) for carcinomatosis. Correcting for the roughly 7% who were men lowered the respiratory cancer figure to 2.0. Even under a year of employment carried substantial mesothelioma risk, highest at three years or more. Mesothelioma deaths occurred from 1963 to 1994. None occurred from 1996 to 2003, when 5.0 would have been expected at the earlier rate. The authors concluded that crocidolite, though durable, appears to be slowly removed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Short report of a mortality follow-up of a historical worker cohort, compared with female death rates for England and Wales (standardised mortality ratios)
• Who was studied: 1154 employees (approximately 93% female) recorded as working on gas mask assembly in a Nottingham factory between 1940 and 1944. 640 had full name and sex recorded (Group A) and 514 had incomplete information (Group B). Mesothelioma rates were based on 1061 workers with recorded duration of employment.
• Exposure: Assembly of military gas masks with filter pads of 80% merino wool and 20% crocidolite. Crocidolite use began in September 1940 (chrysotile had been used in civilian gas masks for less than five months from December 1939). Only duration of employment was available as an index of exposure.
• Main results:
  • 567 (89%) of Group A and 205 (40%) of Group B were traced through 2002
  • Of those traced, 491 (87%) in Group A and 141 (69%) in Group B had died
  • 54 deaths were coded to mesothelioma, and a further 11 deaths coded to other causes were attributed to mesothelioma on pathological evidence
  • All 65 mesothelioma deaths, including six not traced by the ONS, were confirmed pathologically: 47 were pleural and 18 (28%) peritoneal
  • In Group A excluding the 54 deaths coded as mesothelioma (n = 586), the SMR for respiratory cancer was 2.5 (95% CI 1.7 to 3.5), with 32 observed deaths against 13.1 expected. This figure is before the sex adjustment.
  • In the same Group A subcohort, the SMR for carcinomatosis was 3.2 (95% CI 1.8 to 5.4), with 14 observed deaths against 4.4 expected
  • Recalculating expected deaths with male rates for the roughly 7% who were men reduced the respiratory cancer SMR from 2.1 to 1.7 for all 772 traced workers, and from 2.5 to 2.0 for the Group A subcohort
  • The authors suggested the excess from carcinomatosis, ovarian cancer and possibly abdominal cancer may partly reflect undiagnosed mesothelioma. Other causes of death were generally less than expected.
  • The first mesothelioma deaths were two in 1963, and the most recent was in 1994. After about 20 years with no cases, the rate rose rapidly up to 30 years from exposure, then stayed fairly steady for the next 20 years.
  • No mesothelioma occurred between 1996 and 2003. At the 1991 to 1995 rate, 5.0 cases would have been expected in 1938 person-years; observing zero had a probability of 0.0065.
  • Even employment of less than a year carried a substantial mesothelioma risk, and risk was highest at three years or more. In the proportional mortality analysis, mesothelioma accounted for 17/260 (6.5%) of deaths among those employed less than one year and 9/39 (23.1%) among those employed three years or more.
• The authors' conclusion: The authors concluded that the findings confirm a high and specific risk of mesothelioma (28% peritoneal), and perhaps of lung cancer, some 20 to 50 years after brief crocidolite exposure. They also concluded that the statistically significant absence of further cases in the past eight years suggests crocidolite, though durable, is slowly removed.
• Limitations the authors state:
  • There was no information on intensity of exposure to airborne crocidolite; only duration of employment was available
  • The worker list was incomplete because some records had been shredded, and later additions were biased toward mesothelioma cases
  • The low tracing rate (40%) in Group B did not justify further analysis of that group
  • The respiratory cancer SMRs are probably overestimates because they assumed the cohort was entirely female

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Filter pad, Crocidolite, Mesothelioma, Lung Cancer.

Related studies

• Modelling mesothelioma risk for workers assembling military gas masks — J.W. Cherrie, H.A. Cowie, et al. (2007)
• Lung fiber burden in the Nottingham gas mask cohort — G. Berry, F. Pooley, et al. (2009)
• Mortality of two groups of women who manufactured gas masks from chrysotile and crocidolite asbestos: a 40-year follow-up — E.D. Acheson, M.J. Gardner, et al. (1982)
• Asbestos-related cancers among 28,300 military servicemen in the Royal Norwegian Navy — L.A. Strand, J.I. Martinsen, et al. (2010)
• Mesothelioma after crocidolite exposure during gas mask manufacture — A.D. McDonald, J.C. McDonald (1978)
• Mesothelioma risk after 40 years since first exposure to asbestos: a pooled analysis — A. Reid, N.H. de Klerk, et al. (2014)

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