H. M. Jackson to R. C. Smith at Waukegan on Hygienic Dust Control and Threshold Limits (1954)

A two-page memo of December 3, 1954, from H. M. Jackson at J-M headquarters to R. C. Smith at the Waukegan, Illinois, plant, answering questions on dust control. Jackson writes that the American Conference of Governmental Industrial Hygienists' list does not distinguish types of asbestos and sets five million particles per cubic foot, but that "On the basis of the Saranac Research our tentative m.a.c. is 1 million fibers (10 microns and longer) per cubic foot." J-M's clinical experience, he adds, suggested that "Amosite appears to produce asbestosis within a much shorter time than does chrysotile." He also explains how to apply limits to mixed dusts and notes that J-M changed to reporting counts in million fibers per cubic foot in April 1954.

What it shows

Jackson cautions that "neither the threshold limit nor the methods of sampling and counting are absolutes." The limits, he writes, "are not established on the basis of providing an absolutely safe exposure level for every individual," but are a level "within which most individuals will not be harmed," and "no guarantee of full protection can be assured at any level of exposure." Moving a man to a "safe" area must always be followed up medically. J-M's fiber limit grew out of Jackson's 1951 request to Saranac for a fiber standard (Jackson to Vorwald).

In Johns-Manville's chronology

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

Jackson memorandum to R.C. Smith at Waukegan, 12/3/54, stating that the ACGIH standard for amosite is 5 mppcf. Jackson states that J-M's clinical experience suggests that there is a considerable difference in reaction between chrysotile and amosite fibers. The amosite appears to produce asbestosis in a much shorter period of time. Jackson then discusses his formula for mixed dust exposure. He states that the J-M fiber TLV was initiated in April 1954. He also states that neither TLV's nor the methods or counting dust are absolutes.

Editor's note: J-M's description says the ACGIH standard for amosite was 5 mppcf and that J-M's fiber TLV began in April 1954. Jackson's memo says the ACGIH list did not distinguish types of asbestos, and that April 1954 was when J-M changed to reporting counts in million fibers per cubic foot.

Related documents

• H. M. Jackson to G. S. Smith on J-M's Own Threshold Limit for Asbestos (1954)