H. M. Jackson to T. H. Eaton on the Travelers Dust Survey at the Marrero Transite Pipe Plant (1952)

A one-page memorandum of November 11, 1952, from Hugh M. Jackson, Johns-Manville's safety engineer, to T. H. Eaton at the Marrero, Louisiana, plant, sending the Travelers Insurance laboratory's analysis of an October 2 dust survey in the Transite pipe department. Jackson explained that the particle count and the fiber counts measure different things, and gave the limits used: 10 million particles per cubic foot for dust with 5 to 25 percent silica, and 5 million above 25 percent. "Based on the research at Saranac, our tentative m.a.c. for asbestos is 800 thousand fibres per cubic foot."

What it shows

M.a.c. means maximum allowable concentration. Jackson wrote that "the survey indicates excellent control of both dust and fibre exposures," but asked why one room sample in the vent stack department was "so much higher" than elsewhere and why control at a small fitting lathe was less efficient, and asked what steps the plant would take. The memo shows J-M applying its own fiber limit, drawn from the Saranac animal work, alongside the particle limits, as Jackson had proposed to Vorwald in 1951.

In Johns-Manville's chronology

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

Memorandum from H.M. Jackson to T.H. Eaton (Marrero), 11/11/52 re: Travelers Analysis of Samples from the Marrero Plant. TLV for dust containing 5% to 25% silica is 10,000,000 particles per cubic foot; for dust over 25% silica, 5,000,000 particles per cubic foot. "Based on the research at Saranac, out tentative m.a.c. for asbestos is 800 thousand fibers per cubic foot."