Preliminary Report of Mortality Patterns and Occupational Exposures of Mineral Wool Production Workers

Our plain-English summary of Preliminary Report of Mortality Patterns and Occupational Exposures of Mineral Wool Production Workers, by G.O. Ness, J.M. Dement, R.J. Waxweiler, et al (1979).

The study

• Authors: G.O. Ness, J.M. Dement, R.J. Waxweiler, J.K. Wagoner
• Published: Dusts and Disease (1979)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This preliminary report by NIOSH researchers described an air-sampling survey and a retrospective cohort mortality study at a midwestern plant that made rock wool and slag wool, two types of man-made mineral wool fiber. The cohort was 702 white male workers employed at any time from 1940 through 1948 and followed to the end of 1974. By then 199 had died and 33 (5%) were lost to follow-up. Deaths were compared with those expected from United States rates. In 1975 sampling, mean time-weighted average fiber exposures were 0.50 to 0.66 fibers/cc, depending on plant area. About 75% of airborne fibers were of a potentially respirable size. No cause of death was statistically increased among all workers. Beyond 30 years after first employment, deaths from digestive cancer, respiratory cancer and nonmalignant respiratory disease were elevated, but the numbers were small and the excesses were not statistically significant. The authors concluded these excesses should not be dismissed, and said job-history analyses still to come would give a clearer picture.

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: Preliminary report of a retrospective cohort mortality study combined with an industrial hygiene (air sampling) survey
• Who was studied: 702 white male workers at one midwestern rock and slag mineral wool plant (production began 1897) who worked there at any time between January 1, 1940 and December 31, 1948. Vital status was followed to the end of 1974.
• Exposure: Airborne rock wool and slag wool fibers. Slag wool later entirely replaced rock wool. Fibers were made by a steam blowing process thought to have been used until about 1948. In 1975 sampling, the mean time-weighted average exposure was 0.50 to 0.66 fibers/cc, depending on plant area. A clay binder introduced in 1967 added exposure to free crystalline silica.
• Main results:
  • Of the 702 cohort members, 199 (28%) had died by December 31, 1974, and 33 (5%) were lost to follow-up.
  • The cohort contributed 20,126 person-years at risk.
  • About 75% of airborne fibers at the plant were smaller than 3.5 um in diameter and shorter than 50 um in length, which the authors treated as potentially respirable.
  • A bulk sample from the earlier steam blowing process had a significantly lower count median fiber diameter (p less than 0.05) than present-day fibers.
  • Among all plant employees, no cause-of-death category was statistically increased at the time of the report.
  • Beyond 30 years of latency, there were excess deaths from digestive cancer, respiratory cancer and nonmalignant respiratory disease. These excesses rested on small numbers and were not statistically significant.
  • All-cause mortality in the cohort was decreased, which the authors described as showing a 'Healthy Worker Effect'.
  • White male death rates from digestive cancer in the plant's county were markedly lower than United States rates. The authors stated that using county rates would tend to raise the estimated risk of digestive cancer in the cohort.
• The authors' conclusion: The authors concluded that, although no cause of death was statistically increased overall, the long-latency excesses of digestive cancer, respiratory cancer and nonmalignant respiratory disease should not be dismissed as purely artifacts. These are diseases other studies have linked to fiber exposure such as asbestos. The authors suggested that fiber size might explain the digestive cancer increase. They said further analysis by job and an industry study would give a clearer picture of the true risk.
• Limitations the authors state:
  • Detailed job histories had not been fully coded, so this preliminary analysis used only each worker's first and last dates of employment.
  • The long-latency excesses were based on small numbers and were not statistically significant.
  • Expected deaths came from United States rates, which were higher than the county's rates. This would make expected deaths too high, especially for digestive cancer.
  • Pre-employment physicals at the plant may have selected healthier workers, contributing to a healthy worker effect.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, NIOSH, Time-Weighted Average (TWA).

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