W. Clark Cooper and Lewis J. Cralley, Pneumoconiosis in Diatomite Mining and Processing (1958)

A U.S. Public Health Service report of 1958 by Dr. W. Clark Cooper and Lewis J. Cralley on lung disease among workers mining and processing diatomaceous earth (diatomite) in California, Nevada and Oregon, including Johns-Manville's plant at Lompoc, California. Chest X-rays of 869 workers showed changes consistent with pneumoconiosis in 9 percent, with doubtful changes in another 9 percent; among mill workers employed five years or more, about half (48 of 101) had such films. The authors found that the extent of disease "appeared to correlate with cristobalite content of the dust and the length of exposure," cristobalite being the crystalline silica formed when diatomite is calcined.

What it shows

The report recommended keeping dust from cristobalite-bearing products under 5 million particles per cubic foot and amorphous (uncalcined) diatomite dust under 20 million, and that "suitable caution labels should be displayed on all shipping containers for cristobalite-bearing diatomite products." Its acknowledgments thank Dr. K. W. Smith, H. M. Jackson and O. B. Westmont of J-M. The study grew out of the arrangements of 1952 under which the Public Health Service agreed to study the industry (1952 prospectus and agreement). In 1959 Dr. Smith described the study to Lompoc workers as part of J-M's efforts to control disease there (January 1959 memo).

In Johns-Manville's chronology

Johns-Manville's own chronology of what the company knew describes this document as follows:

Report entitled "Pneumoconiosis in Diatomite Mining and Processing" is published by the USPHS. Lompoc plant was included in the survey. J-M invited to review the report before publication. Briefly, the findings were: (a) Diatomite powders containing cristobalite, such as J-M's high-temperature calcined and fluxcalcined materials (Standard Super-Cel and Hyflo Super-Cel) can cause pulmonary damage when inhaled; (b) Natural or uncalcined powders such as Filter-Cel, Celite FC, Celite 379, and Snow Floss are amorphous silicas containing no cristobalite and thus cause little if any trouble when inhaled; (c) Any dust disease caused by diatomite is a separate entity to be differentiated from quartz silicosis; (d) There is no significant difference in the potential health hazard associated with marine or fresh water diatomite; (e) Fewer than 9% of all employees in the diatomite industry surveyed had X-ray evidence of pulmonary reaction to inhaled diatomaceous earth; (f) In working areas where diatomite is used, the dust concentration should not exceed 20 mppcf for non-cristobalite bearing products and 5 mppcf for cristobalite-bearing products. Follow-up studies were conducted by Dr. W.C. Cooper.

Editor's note: Nothing in the report shows that J-M was invited to review it before publication. J-M's description also says fewer than 9 percent of workers had X-ray evidence of reaction; the report counts 9 percent positive and a further 9 percent doubtful.