Insulation workers in Belfast. A further study of mortality due to asbestos exposure (1940-75)

Our plain-English summary of Insulation workers in Belfast. A further study of mortality due to asbestos exposure (1940-75), by P.C. Elmes, M.J. Simpson (British Journal of Industrial Medicine, 1977).

The study

• Authors: P.C. Elmes, M.J. Simpson
• Journal: British Journal of Industrial Medicine
• Published: 1977;34(3):174-80
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002230).

Abstract

A follow-up study of 162 men already working as insulators (laggers) in 1940 has been extended from 1965 to 1975. By the end of 1975 there were 40 survivors when 108 had been expected. Until 1965 there had been an overall excess of deaths; these were due to asbestosis with or without tuberculosis and to alimentary cancer, as well as to bronchial carcinoma and mesothelioma. From 1965 onwards the overall death rate among survivors is not so excessive but there is still a marked excess of deaths from bronchial cancer and mesothelioma. The continued risk of death attributable to malignancy after asbestosis had ceased to contribute directly, does not appear to be caused by any changes which occurred before 1940 in the conditions at work.

In plain English

This study followed 162 men who were already working as insulation workers (laggers) in Belfast in 1940. It extended an earlier follow-up from 1965 to the end of 1975. The authors compared deaths in the group with the deaths expected for men of the same age in Northern Ireland. By the end of 1975, 122 men had died when 54 deaths had been expected. From 1950 to 1964, observed deaths were about three times the expected number. After 1965 the ratio for all causes was 1.5 to 1. This was not significant within each five-year period but was significant when the periods were combined. Asbestosis was an important cause of death until 1964, and three later deaths were still attributed to it. After 1964, however, the excess of deaths over the expected number was entirely due to cancer. From 1950 to 1975, respiratory cancer deaths averaged 15 times the expected number, with no sign of a falling risk. The dust levels and asbestos types could not be estimated. The authors concluded that, for this kind of mixed exposure, a standard based on preventing asbestosis may not adequately protect against cancer.

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: Mortality follow-up (cohort) study comparing observed deaths with deaths expected for men of the same age in Northern Ireland; an extension of an earlier report covering 1940-66
• Who was studied: 162 men (no women) who were working as insulation workers (laggers) in Belfast in 1940, followed to the end of 1975. The original group was 170; five were untraced in the first study and five more were lost to follow-up. In 1940 the men were aged 16 to 66 (mean 36.9 years) and had worked as laggers for up to 35 years (mean 11.3 years).
• Exposure: Asbestos exposure from insulation (lagging) work, described by the authors as mixed exposure. The dust concentrations and types of asbestos could not be estimated. The authors note that since 1965 very little asbestos other than Marinite board was used in ships made in Belfast.
• Main results:
  • By the end of 1975 there had been 122 deaths in the group when 54 had been expected.
  • Survival among the laggers was significantly lower than expected from 1950 onwards (chi-square 33.3; p less than 0.001).
  • From 1950 to 1964, the ratio of observed to expected deaths from all causes was approximately 3 to 1 and highly significant.
  • After 1965, the ratio for deaths from all causes was 1.5 to 1. The difference was not significant within each five-year period, but there was a significant excess when the two periods were combined (chi-square 7.2; p less than 0.01).
  • In the first 10 years only 4 of 17 deaths were due to cancer. In the last 11 years, 22 of 28 deaths were due to cancer.
  • Of the respiratory cancers, 24 were classified as bronchial carcinoma and 8 as definite mesothelioma (listed in Table 2a as pleural mesothelioma). In 11 further cases the evidence could not distinguish between the two.
  • Of five peritoneal mesotheliomas, two were fully proved. In three a primary alimentary (digestive tract) tumour was possible.
  • From 1950 onwards, the ratio of observed to expected deaths from all types of cancer averaged 7 to 1.
  • For respiratory cancer, the ratio of observed to expected deaths was 18 to 1 in 1950-54 and averaged 15 to 1 over 1950-75, with no evidence of a declining risk in the last 10 years.
  • Asbestosis continued to be an important cause of death until 1964.
  • Table 2b attributes 16 deaths to asbestosis in total. These include two in 1965-69 and one in 1975. The authors describe a gradual disappearance of asbestosis as a primary cause of death since 1965.
  • From 1950 to 1964 there were 52 more deaths than expected. 35 of the excess were from cancer, leaving 17 attributable to non-malignant disease. In that period, 17 deaths were attributed to asbestosis with or without tuberculosis.
  • After 1964 the excess deaths over the expected number were entirely attributable to malignant disease.
  • Comparing men who started work before 1933 with those who started after showed no difference in survival. Comparing men who first started work before and after age 25 also showed no difference.
  • Workers with 29 years' exposure or less had a relative excess of deaths from asbestosis with or without tuberculosis. Those with more than 29 years' exposure had a relative excess of deaths from asbestos-related cancer.
• The authors' conclusion: The authors concluded that this kind of mixed exposure carries a significant risk of bronchial cancer even when asbestosis is no longer a significant cause of death. They added that, for mixed exposure, a standard based on preventing asbestosis may not adequately protect against cancer.
• Limitations the authors state:
  • The study was not complete: 40 of the 162 men were still alive.
  • Dust concentrations and asbestos types could not be estimated.
  • Men who started work after 1940 were excluded, so changes in risk since then could not be evaluated.
  • Mesothelial tumours were difficult to tell apart from epithelial tumours, in both respiratory and gastrointestinal cancers.
  • Numbers were too small to estimate the relative risk of other cancers.
  • The analysis by duration of exposure was difficult because many men worked until they died, so early death was linked with short exposure.
  • Such studies are hard to extend beyond a single factory or town, so unknown local factors may be present.

Topics

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

Medical terms in this study, explained in our Lexicon: Insulator, Asbestos Exposure, Carcinoma, Mesothelioma.

Related studies

• Insulation workers in Belfast. 3. Mortality 1940-66 — P.C. Elmes, M.J. Simpson (1971)
• Insulation workers in Belfast. 1. Comparison of a random sample with a control population — W.F. Wallace, J.H. Langlands (1971)
• Asbestos, mesothelioma and the legacy of shipbuilding in Belfast — P.J. Morrison (2008)
• Relationship between exposure to asbestos and pleural malignancy in Belfast — P.C. Elmes, O.L. Wade (1965)
• Mortality among workers exposed to asbestos at the shipyard of Genoa, Italy: a 55 years follow-up — D.F. Merlo, M. Bruzzone, et al. (2018)
• Mortality experience of insulation workers in the United States and Canada, 1943--1976 — I.J. Selikoff, E.C. Hammond, et al. (1979)

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