H. M. Jackson to Arthur J. Vorwald Asking for a Fiber Count Standard (1951)

A one-page letter of July 27, 1951, from Hugh M. Jackson, Johns-Manville's safety engineer, to Dr. Arthur J. Vorwald of the Saranac Laboratory. Thanking Vorwald for his report on experimental asbestosis, Jackson writes that J-M's industrial hygiene surveys had for six or eight months been counting fibers 10 to 15 microns and longer, "since a concentration of .8 million fibres per cubic foot brought about development in the experimental animals." He asks whether "one million fibres per cubic foot" would be a satisfactory standard, adding: "We realize that there is little concrete evidence to substantiate any particular figure but your opinion in this matter would be most helpful to us."

What it shows

The dust limit then in general use for asbestos was five million particles per cubic foot, a count of all particles rather than fibers (see the 1947 limits of the American Conference of Governmental Industrial Hygienists). Jackson's letter shows that J-M's own safety staff had begun counting fibers because the Saranac animal work produced disease at 0.8 million fibers per cubic foot, and that they recognized there was no firm basis for any safe figure. The file does not include a reply from Vorwald.

In Johns-Manville's chronology

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

Jackson writes Vorwald on 7/27/51 and requests a tentative fiber TLV, acknowledging that "there is little concrete evidence to substantiate any particular figure but your opinion in this matter would be most helpful to us." Vorwald suggests .8 million or 1 million fiber standard. Based on Saranac guinea pig study British researchers (King) documented effects in rabbits using fibers 2.5 micron and longer.

Editor's note: J-M's description says Vorwald suggested a standard of 0.8 or 1 million fibers and mentions British work by King. This file holds only Jackson's letter: it is Jackson who proposes one million fibers per cubic foot, 0.8 million is the concentration that affected the experimental animals, and no reply from Vorwald is included.

Related documents

• American Conference of Governmental Industrial Hygienists Adopts Its 1947 Limits, Including Asbestos (1947)