H. Rosovsky to J. O. Eby Comparing Travelers and Canadian J-M Fiber Counts (1955)

A one-page memo of March 30, 1955, from H. Rosovsky to J. O. Eby at Canadian Johns-Manville, answering H. M. Jackson's letter of March 16 on dust counts in the No. 5 Mill. To compare fiber counting, three pairs of duplicate samples were counted by the Travelers Insurance Company's laboratory in Hartford and by the Canadian J-M clinic. Particle counts were about the same, but the fiber counts were ten times higher by Travelers than by the clinic; a year earlier the difference had been as high as 200 times. Because authorities disagreed on whether particles or long fibers were more hazardous, Rosovsky recommends adding the two into a "Total Dust Count" and keeping it at or below five million particles per cubic foot.

In Johns-Manville's chronology

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

Letter from H. Rosovsky to J.O. Eby, 3/30/55, re: H.M. Jackson letter of 3/16/55, comparison of Travelers and CJM fiber counts for duplicate samples. Particles equate but Travelers reported ten times the fibers; 1954 difference was 200 fold. Recommends adding particles and fibers for a "Total Dust Count" to be within 5 mppcf.