H. M. Jackson to T. R. Turnbull on Perlite Dust in Asbestos Pipe Covering (1949)

A one-page memo of April 25, 1949, from H. M. Jackson of Johns-Manville to T. R. Turnbull on the use of perlite in making asbestos pipe covering. A survey made on January 14, 1949, by the Industrial Health Section of the Metropolitan Life Insurance Company found dust counts "high for even a nuisance dust," and because the perlite was about 13.5% free silica, the concentrations were "considerably higher" than the 20 million particles per cubic foot allowed by the New Jersey State Department of Health code. Jackson recommended "adequate provision" for ventilation and dust control in every product line where perlite was being considered.

What it shows

No crystalline silica was found under the microscope, so Jackson took the silica to be amorphous. That form, he wrote, "cannot be considered innocuous" and was known to have caused lung damage, citing tentative conclusions of the Saranac researchers who had studied J-M's diatomaceous earth (see the 1937 Lompoc X-rays). Perlite went into Thermobestos, the amosite pipe covering J-M planned to make later that year (the Thermobestos report).

In Johns-Manville's chronology

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

In a memorandum dated 4/25/49, Jackson reports on results of industrial hygiene survey conducted by Metropolitan on the use of perlite in the manufacture of asbestos pipe covering. The survey showed: high dust counts even for a nuisance dust; a free (crystalline) silica content of approximately 13.5%; and free silica of an amorphous type which, while not as harmful as the crystalline forms, has been known to cause lung damage. Jackson recommends that adequate provision be made for ventilation and dust control when using perlite in the manufacture of asbestos pipe covering.

Editor's note: J-M's description calls the 13.5% free silica in the perlite crystalline. The memo says the silica was "apparently of an amorphous type since no crystalline forms were determined on microscopic examination."