T. J. Weeks and A. F. Burns on Testing J-M's Dust Mask at the U.S. Bureau of Mines (1969)

A 12-page confidential memorandum (M404-66) of February 4, 1969, from T. J. Weeks and A. F. Burns of the Johns-Manville Research and Engineering Center, reporting on their January 13–15 visit to the U.S. Bureau of Mines to test dust masks against silica, coal and asbestos dust. In two of three silica tests, J-M's own experimental mask let through more dust than Bureau specifications allowed. In the asbestos test, eight masks were challenged with finely milled chrysotile fiber (Plastibest 20), and only one let through more than 1 per cent; the appendices hold diagrams of the test chambers and electron micrographs of the fiber.

What it shows

The memo records J-M's early work toward selling its own dust mask, which the writers expected to make cheaper by dropping the exhalation valve and the silicone gum seal. They noted "a considerable lack of information" on filters against fiber and "excitement" over Leroy Balzer's reports of "significant amosite fiber breakthrough," and proposed writing their results up at once for the AIHA Journal; the Bureau's engineer asked that his name be left off, and said that "inasmuch as we may become a dust mask manufacturer" he would not discuss the results with anyone. The paper appeared the next year as "Performance of Dust Respirators Against a Fibrous Dust". The memo also lists the filter of the American Optical mask as "crocidolite, glass, and nylon."