E. M. Fenner's Report of the Environmental Control Subcommittee Meeting on Electron Microscope Counts and a New Fiber Limit (1970)

A confidential three-page report of February 2, 1970, by E. M. Fenner, J-M's director of environmental control and secretary of its Environmental Control Subcommittee, on the subcommittee's January 19 meeting, with attachments. A special survey at the Jeffrey mill had compared light microscope counts of membrane filter dust samples with electron microscope counts, mainly to learn how many fibers were too fine for the light microscope to see; so far, the report says, a correlation between the two was "not possible." Dr. G. W. Wright, J-M's medical consultant, expected the American Conference of Governmental Industrial Hygienists to set a threshold limit of 5 fibers per cubic centimeter in April 1970, and the subcommittee recommended that J-M adopt 5 as its respirator level and 2 as its out-of-control and engineering level, in place of its existing levels of 12, 6 and 2.

What it shows

The subcommittee planned more sampling at the Jeffrey Mine, including ambient air, with checks against the electron microscope work of Mount Sinai's Environmental Sciences Laboratory. The report also records J-M's agreement to serve as a subcontractor on a federal National Air Pollution Control Administration document on controlling asbestos emissions, on the condition that emissions for individual plants would not be disclosed. An attachment lists dust stations over the limit in a November 1969 survey of the Pittsburg, California, plant, several with no protective equipment listed; "no decision was made" on the next step. The 1970 ACGIH list itself is a separate entry.

In Johns-Manville's chronology

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

Report dated 2/2/70, prepared by E.M. Fenner, of J-M Environmental Control Subcommittee meeting held on 1/19/70. (7 attachments) J-M attempted to compare membrane filter asbestos fiber counts analyzed by a a light microscope with those analyzed by an electron microscope. The main purpose of the study was to determine the number of fibers in the sample that are not visible by light microscope. Results of these efforts were noted in an attachment to these minutes. No correlation could be established between light microscope and electron microscope results.

Dr. Wright stated that he believed that the ACGIH recommended TLV for asbestos fiber would become 5 f/cc in April of 1970. In light of this, the environmental control subcommittee recommended that the new J-M standards be 5 f/cc (respiratory protection required) and 2 f/cc (station out of control and corrective measures required; and engineering standard for new and rebuilt dust control systems).

Related documents

• American Conference of Governmental Industrial Hygienists, Threshold Limit Values for 1970, with a Proposed Asbestos Limit of 5 Fibers (1970)