Dr. Kenneth Smith to A. O. Smith Corporation on Rock Wool (1958)

A two-page letter of May 6, 1958, from Dr. Kenneth W. Smith, Johns-Manville's medical director, to the personnel director of the A. O. Smith Corporation, which had asked about health hazards in handling J-M's rock wool. Smith wrote that to the best of J-M's knowledge its mineral fiber "does not contain any free silica, nor does it produce any form of pulmonary fibrosis or pneumoconiosis." He cited published studies and an old Metropolitan Life Insurance Company survey of a J-M mineral wool plant, and said the only problem seen was occasional skin irritation, which long sleeves, a buttoned collar and a shower would reduce.

In Johns-Manville's chronology

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

On 5/6/58, K.W. Smith responds to inquiry of A.O. Smith Corp. J-M's rock wool poses no pulmonary risk since it does not contain free silica.