Difficulties of attribution of effect in workers exposed to fiberglass and asbestos

Our plain-English summary of Difficulties of attribution of effect in workers exposed to fiberglass and asbestos, by K.H. Kilburn, R.H. Warshaw (American Journal of Industrial Medicine, 1991).

The study

• Authors: K.H. Kilburn, R.H. Warshaw
• Journal: American Journal of Industrial Medicine
• Published: 1991;20(6):745-51
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004911).

Abstract

Man-made mineral fibers have many properties of asbestos that raise concern about their safety. We studied 175 fiberglass production workers, using chest radiographs, measurement of total lung capacity, chest examinations, and occupational and medical histories. Pulmonary volumes and flows were calculated as percent of predicted, adjusted for height, age, ethnicity, and cigarette smoking. Thirty-one men with radiographically evident small irregular opacities of profusion of 1/0 or greater and/or pleural abnormalities were observed. Eight of 38 men with such changes said they had been exposed only to fiberglass; the other 23 with radiologically detectable pleural and/or pulmonary changes were among the 137 whose histories indicated that they had been exposed to asbestos and to fiberglass. Pulmonary function measurements as group means were reduced in the 175: FVC was 94.8% predicted, FEV1 was 91.3% predicted, FEF25-75 was 80.7% predicted, FEF75-85 was 73.1% predicted and FEV1/FVC was 0.73. Total lung capacity (TLC) was elevated to 114.2% predicted (mean) and RV/TLC (mean 0.46) was also elevated. Although only 78% of fiberglass production workers gave histories of asbestos exposure, all had shared the air in a manufacturing plant where ovens insulated with asbestos were continuously cleaned, repaired, dismantled, and rebuilt. It appears that attribution of the effects of their exposure to fiberglass could not be estimated independently of the effects of asbestos exposure.

In plain English

This study examined 175 workers from a rotary spun fiberglass plant in production since 1947. They were invited through their unions. The workers had chest X-rays, lung function tests, questionnaires and chest examinations. Of these, 137 reported asbestos exposure, mostly from asbestos insulation on the plant's ovens. The other 38 said they had not been exposed to asbestos. The asbestos fiber type is not named. X-ray changes of the lung tissue or pleura were seen in 8 of 38 workers (21%) without known asbestos exposure and in 23 of 137 (16.8%) of those reporting asbestos exposure, 17.7% overall. Among men 15 or more years from first exposure, the figure was 33% (28 of 84). As group averages, airflow measures were reduced and total lung capacity was raised. Among men over 49 who had ever smoked, the 25 with X-ray changes had greater lung function impairment than the 48 without, after adjustment for age, ethnicity and smoking duration. The authors concluded that a combined effect of asbestos and fiberglass was probable, and that effects could not be attributed to fiberglass on its own.

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: cross-sectional medical examination of a group of workers from one plant (chest X-rays, lung function tests, questionnaires, chest examination)
• Who was studied: 175 workers (163 men, 12 women; mean age 51.2 years) from a rotary spun fiberglass manufacturing factory in production since 1947. About 700 were invited: 500 production workers who were members of the International Association of Heat and Frost Insulators and Asbestos Workers, about 100 retirees and 100 maintenance workers. 189 made appointments. Location of the plant not stated.
• Exposure: Rotary spun fiberglass, plus asbestos-containing insulating materials, particularly from the ovens used to set the resin binder of fiberglass batts. 137 workers reported asbestos exposure; 38 said they had none. Asbestos fiber type not specified.
• Main results:
  • Among the 38 workers without known asbestos exposure, 8 (21%) had lung tissue or pleural X-ray abnormalities of the kind generally associated with asbestos exposure.
  • Among workers reporting asbestos exposure, 23 (16.8%) had such abnormalities. The text prints the denominator as 147, but the abstract and Table II give 137.
  • Overall, 17.7% of the 175 workers had chest X-ray abnormalities.
  • Among men 15 or more years from beginning exposure to fibers, 33% (28 of 84) had X-ray abnormalities.
  • The profusion of irregular opacities on the X-rays was in ILO categories 1/0 to 1/2.
  • As group means for all 175 workers, FVC was 94.8% of predicted and FEV1 91.3% of predicted, while total lung capacity was elevated to 114.2% of predicted.
  • In the age-matched comparison of Table IV, the comparison was between 25 workers with X-ray abnormalities and 48 without, all over age 49 and all having ever smoked. Those with abnormalities had greater lung function impairment after adjustment for age, ethnicity and duration of smoking. The text describes the comparison group differently (63 of 132 men older than 50).
• The authors' conclusion: The authors concluded that a combined effect of exposure to asbestos and to fiberglass was probable. In their view, given the known asbestos exposure, effects in this group could not be attributed to fiberglass separately.
• Limitations the authors state:
  • Even the 38 workers who denied asbestos exposure may have been unaware of exposure as bystanders while ovens were cleaned, repaired, dismantled and rebuilt.
  • Confirming a combined effect would require analysis of fiber burden in the lungs.
  • The total numbers were small, so the low profusion of opacities should not be taken to reflect lesser exposure.

Topics

Medical terms in this study, explained in our Lexicon: Attribution, Mineral Fiber, Chest X-Ray, Total Lung Capacity (TLC), FEV1, FEV1/FVC Ratio, Asbestos Exposure.

Related studies

• Historical cohort study of US man-made vitreous fiber production workers: I. 1992 fiberglass cohort follow-up: initial findings — G.M. Marsh, A.O. Youk, et al. (2001)
• Flame-attenuated fiberglass: another asbestos? — K.H. Kilburn (1982)
• Pulmonary response of mice to fiberglass: cytokinetic and biochemical studies — I.Y. Adamson, H. Prieditis, et al. (1995)
• Comparative pulmonary responses to inhaled inorganic fibers with asbestos and fiberglass — K.P. Lee, C.E. Barras, et al. (1981)
• A case-control study of malignant and non-malignant respiratory disease among employees of a fiberglass manufacturing facility. II. Exposure assessment — L. Chiazze, D.K. Watkins, et al. (1993)
• Constrictive pericarditis in a patient with fiberglass lung disease: a case report — C.Y. Hsu, H.Y. Chen, et al. (2024)

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