A 21 Year Radiographic Follow Up of Workers in the Diatomite Industry

Our plain-English summary of A 21 Year Radiographic Follow Up of Workers in the Diatomite Industry, by W.C. Cooper, G. Jacobson (1975).

The study

• Authors: W.C. Cooper, G. Jacobson
• Published: Presented at the XVIII International Congress on Occupational Health, Brighton, England. 14-19 September. (1975)
• 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 conference paper reported a 21-year chest X-ray follow-up at one diatomite quarry and processing plant in the western United States, first surveyed by the Public Health Service in 1953-54. Diatomite is a natural silica. Heating it (calcining) turns part of it into cristobalite. The paper concerns silica dust, not asbestos. The authors reviewed the latest annual film of 428 workers employed on July 1, 1974 with at least 5 years of service, and of 80 workers with 5 or more years of service who left between 1969 and 1974. Of the 428, 20 (4.7%) had films read as positive. After excluding changes present at hire or judged not to be pneumoconiosis, 12 (2.8%) were regarded as probably diatomite pneumoconiosis, and all but one had been employed before 1953. Four had large opacities, all in the smallest category (A), compared with 26 workers with large opacities in 1953. One excluded worker had mainly pleural changes that the authors said resembled asbestosis. The authors attributed the near-elimination of new cases to strict dust control and mandatory respirators.

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: Radiographic (chest X-ray) follow-up of a work force 21 years after an earlier survey: review of the latest annual film of current and recently terminated employees, plus serial follow-up of workers with abnormal films in 1953
• Who was studied: One diatomite plant (quarry and mill) that provided 591 of the 869 workers in the 1953-54 study. Of 617 employees on July 1, 1974, 428 had 5 or more years of service. Also 80 employees who left between July 1, 1969 and July 1, 1974 after 5 or more years.
• Exposure: Diatomite dust (amorphous silica), natural, straight-calcined and flux-calcined. Calcining produces crystalline cristobalite, and major cristobalite exposures occurred in the processing mill. About 11% of workers were in quarries with exposure only to crude diatomite.
• Main results:
  • Among the 428 current employees with 5 or more years of service, 20 (4.7%) had films read as positive for pneumoconiosis (UICC/Cincinnati 1/1 or higher).
  • In 8 of these 20, the changes were present on pre-employment films or were not regarded as pneumoconiosis. That left 12 (2.8%) of the 428 regarded as probably diatomite pneumoconiosis, and all but one of the 12 had been employed before 1953.
  • Only one current employee with less than 20 years of experience (hired since the 1953 study) had a positive film, classified 1/1 with some uncertainty because the film was partially fogged.
  • Of 129 current employees with 20 or more years on the work force, 11 had positive films. Of these 11, four had been negative in 1953, one doubtful and six positive, and all but one had mill exposure to cristobalite.
  • Four current employees had large opacities, all category A, with employment histories of 27, 27, 44 and 46 years. No current employee had massive coalescent lesions (B or C), which were common in the earlier survey.
  • In 1953, large opacities had been found in 26 workers, with exposures of 4 to 37 years (mean 17.8, median 18 years).
  • Among the 80 terminated employees, none of the 46 with less than 20 years of service had films read 1/1 or higher. Simple pneumoconiosis was found in 4, and progression in 5 who had been positive in earlier surveys.
  • Of 52 workers with suspect films in 1953, 44 had later films. In 22 the last film was negative, in 20 still doubtful, and in only 2 did definite pneumoconiotic changes develop.
  • Of 26 employees with complicated pneumoconiosis (large opacities) in 1953, 23 had follow-up films: 4 showed no progression, 14 slight progression and 5 marked progression.
  • One worker (24 years of service, shipping department, with prior welding and mining) was excluded because his changes were mainly pleural, confined to the left lower lung zone, and resembled asbestosis rather than diatomite pneumoconiosis.
• The authors' conclusion: The authors attributed the almost complete elimination of new cases of diatomite pneumoconiosis to strict dust control programs, supplemented by mandatory respirator use at jobs with high risk of cristobalite exposure.
• Limitations the authors state:
  • Because of the respirator program, the authors said it was impossible to attribute control of pneumoconiosis entirely to meeting the desired time-weighted average exposure levels.
  • The film classification criteria used in 1953 were somewhat different from those used now.

Topics

Medical terms in this study, explained in our Lexicon: Chest X-Ray, Pneumoconiosis, Dust Control, Respirator.

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