Mortality of UK electricity generation and transmission workers, 1973-2002

Our plain-English summary of Mortality of UK electricity generation and transmission workers, 1973-2002, by L. Nichols, T. Sorahan (Occupational Medicine, 2005).

The study

• Authors: L. Nichols, T. Sorahan
• Journal: Occupational Medicine
• Published: 2005;55(7):541-8
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To examine mortality from cancer and non-malignant causes among a large cohort of UK electricity generation and transmission workers.

Methods: The mortality experienced by a cohort of 83,923 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2002. All employees had worked for at least 6 months with some employment between 1973 and 1982. Standardized mortality ratios (SMRs) were used to assess mortality in the total cohort and in three sub-cohorts: power station workers, substation and transmission workers and workers at non-operational locations. These classifications were based on the place of work of the first known job.

Results: Overall mortality was significantly below that expected, based on national rates [males: observed (Obs) 18,773, expected (Exp) 22,497.9, SMR 83; females: Obs 1122, Exp 1424.9, SMR 79]. Statistically significant deficits of deaths were also found for most of the major disease groupings. However, significant excesses of deaths were found in male power station workers for cancer of the pleura (Obs 129, Exp 30.3, SMR 426) and in male workers from non-operational locations for cancer of the brain (Obs 55, Exp 36.0, SMR 153). There was also a non-significant excess of deaths from cancer of the breast in male power station workers (Obs 10, Exp 5.3, SMR 190).

Conclusions: Mortality was exceptionally low for most causes of death but late health effects from earlier asbestos exposure were still in evidence.

In plain English

The authors followed 83,923 people employed at least six months by the Central Electricity Generating Board of England and Wales, with some employment between 1973 and 1982, and compared their deaths from 1973 to 2002 with national rates. Overall deaths were below expected for men (18,773 observed, 22,497.9 expected) and women (1,122 observed, 1,424.9 expected). Men whose first known job was at a power station had excess deaths from pleural cancer (129 observed, 30.3 expected; standardized mortality ratio 426, where 100 means as expected). They also had excess deaths from peritoneal cancer (14 observed, 7.6 expected) and asbestosis (20 observed, 3.5 expected). The pleural excess was larger among earlier hires and grew with time since first employment. Men grouped under non-operational locations had excess deaths from pleural cancer (17 observed, 8.6 expected) and brain cancer (55 observed, 36.0 expected). Noting that asbestos was widely used in power stations for lagging pipes and boilers, the authors concluded that late health effects of earlier asbestos exposure were still evident. They acknowledged that grouping workers by first known job probably misclassified some.

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: Cohort mortality study comparing observed deaths with those expected from national rates for England and Wales (standardized mortality ratios), with sub-cohorts defined by the work location of the first known job
• Who was studied: 83 923 employees (72 889 males, 11 034 females) of the former Central Electricity Generating Board of England and Wales. All had at least 6 months employment, with some employment between 1973 and 1982. Follow-up ran from 1973 to 31 December 2002. Sub-cohorts were defined by the location of the first known job: power stations (53 265), substation or transmission sites (3223) and non-operational locations (22 327). 5108 people could not be classified.
• Exposure: Employment in electricity generation and transmission, grouped by work location of the first known job. Asbestos exposure was not measured. The authors noted that asbestos was widely used in power stations for lagging pipes and boilers. No fiber types are named.
• Main results:
  • All-causes mortality in the total cohort was significantly below national rates. Males: observed 18 773, expected 22 497.9, SMR 83. Females: observed 1122, expected 1424.9, SMR 79.
  • Males in the total cohort had a significant excess of deaths from cancer of the pleura: 166 observed, 43.4 expected, SMR 383. The article's text prints the expected figure as 'Obs 43.4', but its Table 2 gives Exp 43.4.
  • Male power station workers (first known job at a power station) had a significant excess of deaths from cancer of the pleura: 129 observed, 30.3 expected, SMR 426.
  • Male power station workers had a significant excess of deaths from cancer of the peritoneum: 14 observed, 7.6 expected, SMR 185. For 13 of these 14 men, the underlying cause of death was described as peritoneal malignant mesothelioma.
  • Male power station workers had a highly elevated rate of death from asbestosis: 20 observed, 3.5 expected, SMR 574, 95% CI 351 to 887.
  • Among male power station workers, the pleural cancer SMRs showed a significant negative trend by year of hire: earlier decades of hire had higher SMRs. The highest was for men hired in 1950 to 1959 (45 observed, 6.5 expected, SMR 697).
  • Among male power station workers, pleural cancer SMRs rose steadily with time since first employment. The highest was at 30 or more years (82 observed, 13.8 expected, SMR 594).
  • 532 deaths in the study were classified as malignant neoplasm without specification of site. On review of these death certificates, 109 (20.5%) were mesotheliomas, 85 of them in power station workers. Unspecified mesotheliomas were excluded from both the observed and expected numbers for cancer of the pleura.
  • Male workers grouped under non-operational locations had significant excesses of deaths from cancer of the pleura (17 observed, 8.6 expected, SMR 197) and cancer of the brain (55 observed, 36.0 expected, SMR 153).
  • Of the 17 male non-operational workers who died from mesothelioma, further job history was found for 11. All 11 had potential for asbestos exposure at other sites and facilities: 4 through power station construction and commissioning, 2 through occasional work at power stations, 4 through earlier power station employment, and 1 possibly through earlier employment in other industries.
  • Male substation and transmission workers had no excess mortality from cancer of the pleura. Their overall mortality was below expectation: 710 observed, 1005.6 expected, SMR 71.
  • Male power station workers had a non-significant excess of deaths from breast cancer: 10 observed, 5.3 expected, SMR 190. The authors said it would be unwise to attach too much importance to this.
• The authors' conclusion: The authors concluded that mortality was exceptionally low for most causes of death, but that late health effects from earlier asbestos exposure were still in evidence. They judged that most of the pleural cancer excess in power station workers was a consequence of asbestos exposure.
• Limitations the authors state:
  • Workers were grouped by first known job rather than first job, and 55% had some employment before personnel records were computerized. The authors said some misclassification of work location is almost certain.
  • Comparing with national rates, where a healthy worker effect and higher socio-economic status may lower mortality, can cause health effects to be missed.
  • Some findings, such as the excess of gall-bladder cancer in women at non-operational locations (based on five deaths), may be due to chance given the large number of significance tests.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Power plants and utilities.

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), Pleura, Asbestos Exposure.

Related studies

• Occupational respiratory cancer and exposure to asbestos: a case-control study in a cohort of workers in the electricity and gas industry — E. Imbernon, M. Goldberg, et al. (1995)
• Mortality among workers in the geothermal power plants at Larderello, Italy — E. Pira, M. Turbiglio, et al. (1999)
• Asbestos risk among full-time workers in an electricity-generating power station — A. Hirsch, L. Di Menza, et al. (1979)
• Risk of cancer among Danish utility workers--a nationwide cohort study — C. Johansen, J.H. Olsen (1998)
• Mortality rates among nuclear industry workers at Lucas Heights Science and Technology Centre — R.R. Habib, S.M. Abdallah, et al. (2005)
• Cancer in electrical workers: an analysis of cancer registrations in England, 1981-87 — N.T. Fear, E. Roman, et al. (1996)

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