W. C. L. Hemeon, Report of Preliminary Dust Investigation for the Asbestos Textile Institute (1947)

A 30-page report dated June 18, 1947, by W. C. L. Hemeon, head engineer of the Industrial Hygiene Foundation of America in Pittsburgh, written for the Asbestos Textile Institute after visits to its members' textile plants. Only five plants had ever X-rayed their workers. Where X-rays had been taken, two plants appeared to have about 20 percent of their employees affected by asbestosis, and Hemeon "strongly recommended" X-ray examinations of all exposed workers. He warned that keeping dust under the accepted limit of five million particles per cubic foot "does not positively insure" that workers will not get asbestosis after a long working life.

What it shows

This is the first detailed challenge in the industry's own files to the dust limit that came out of the U.S. Public Health Service's 1938 Dreessen study (see Threshold Limit Value (TLV)). Hemeon pointed out that the study had "abnormally few" workers exposed more than 15 years. The available information, he wrote, "does not permit complete assurance that five million is thoroughly safe." Electron microscope pictures taken in a well-controlled card room showed many fibers up to 50 microns long but so thin they were "invisible in the dust counting microscope." So the standard dust count could miss the very particles that might cause disease. He also questioned the practice in several plants of returning filtered air from dust collectors to the workroom. He proposed periodic medical examinations, a diagnostic panel to read X-rays, and a study of existing records from North Carolina and Metropolitan Life. The report ends by calling this a program "aimed at the elimination of asbestosis cases" from members' plants. A handwritten note on the cover refers to ATI meetings of November 1947 and June 1948 "rejecting dust study proposal," and a margin note marks Plant H, which found five or six early cases a year, as J-M.

In Johns-Manville's chronology

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

"Report of Preliminary Dust Investigation for ATI" of June, 1947; Hemeon study (IHF Engineer) questions adequacy of the 5 mppcf standard; Copied to J-M and other IHF members but not publicly distributed. First significant challenge to TLV. Notes possible progress; effects of long term low exposures (implicit criticism of Dreessen); need to study medical records; suggests use of diagnostic expert panel; questions recycling air from dust control systems. Notes dust counts may be grossly inaccurate due to failure to detect fibers.

Editor's note: J-M's description says the report was copied to J-M and other IHF members but not publicly distributed. The report itself does not show how it was distributed.