H. M. Jackson to George Finley of Black, Sivalls & Bryson on 85% Magnesia (1957)

A two-page letter of March 15, 1957, from H. M. Jackson, manager of J-M's Industrial Health Program, to George Finley, personnel manager of Black, Sivalls & Bryson, Inc., who had asked about J-M's 85% Magnesia insulation. Jackson writes that the product contains about 12 percent asbestos fiber and that, to the extent fiber is in the dust from cutting and fitting, "there may be a possible health hazard which should be controlled." He points Finley to the American Conference of Governmental Industrial Hygienists' limit of 5 million particles per cubic foot for asbestos dust.

What it shows

Jackson explains that in J-M's experience asbestosis "results from heavy exposure over a long period of time," with ten or more years needed for disabling disease, and cites Dr. Arthur Vorwald's 1951 "Experimental Studies of Asbestosis." He describes J-M's own controls: ventilation at the point of operation, vacuum cleaning, U.S. Bureau of Mines approved respirators, careful work methods, and periodic examinations and chest X-rays reviewed by a doctor. The letter shows J-M telling a customer that cutting one of its insulation products could create a hazard that needed control.

In Johns-Manville's chronology

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

Letter from Jackson to George Finley, Black, Sivalos & Bryson, Inc., 3/15/57. Finley had written requesting information concerning J-M's 85% magnesia products. Jackson advised that these products contained approximately 12% asbestos fiber and therefore a possible health hazard was posed during operations such as cutting and fitting. He suggested that the 5 mppcf standard be adhered to.