Document EB773M2m27G6r3yxV5bDXwYx

January 26, 1966 Mr Charles B Mallory Works Manager American Brake Shoe Company Winchester, Virginia Dear Mr. Mallory The analysis of the air samples collected in your plant during our survey in September, 1965 has been completed, and the results are attached. The impinger samples were counted during the survey using the American Conference of Governmental Industrial Hygienists' method. The membrane filters were rendered transparent with a 50-50 mixture of diethyl oxalate, dimethyl phthalate and counted at 43Ox magnification with phase contrast illumination. All ofthe dust concentrations as measured by impingers were under the 5 million particle per cubic foot Threshold Limit Value currently in use The membrane filter method is experimental and no standards have been set for its interpretation. Some relationships between the impinger and filter measurement are discussed in the enclosed reprint Your cooperation in this study is sincerely appreciated, and the data gained from your plant is of considerable value Sincerely yours. Enclosure cc (Through State Health Commissioner) cc B Weidner, Research Director, NIOSH Jeremiah R. Lynch Senior Sanitary Engineer Engineering Section Research and Technical Service Branch