H. M. Jackson to Dr. R. E. Joyner of Carbide and Carbon Chemicals on Superex and Thermobestos Insulation (1956)

A two-page letter of August 22, 1956, from H. M. Jackson, manager of J-M's industrial health program, to Dr. R. E. Joyner, medical director of Carbide and Carbon Chemicals Company in Texas City, Texas, answering his request for information on Thermobestos and Superex insulation. Jackson explains that the calcined diatomaceous earth in Superex is partly converted to crystalline silica (cristobalite), which can cause lung fibrosis, and cites a recommended limit of five million particles per cubic foot. He describes Thermobestos as containing "expanded perlite" and discusses perlite dust. For both dusts he lists J-M's controls: local ventilation, vacuum cleaning, "U. S. Bureau of Mines respirators for intermittent exposures," care to avoid bag breakage and housekeeping.

What it shows

The letter says nothing about asbestos, although J-M's own sworn answers in the Le Grande case list Thermobestos as 10 to 15 percent asbestos and Superex as 5 to 10 percent. According to J-M's description, Jackson later wrote again to correct himself, saying Thermobestos was calcium silicate with about 10 percent asbestos fiber; that letter is not in this file.

In Johns-Manville's chronology

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

Letter from Hugh Jackson to R.E. Joyner, Medical Director, Carbide and Carbon Chemicals Company dated 8/22/56 concerning the raw materials and potential hazards associated with Thermobestos. Jackson retracts information in a letter dated 8/22/56 wherein he erroneously stated that Thermobestos contained Perlite. He correctly advises that Thermobestos in fact consists primarily of calcium silicate and a small percentage (approximately 10%) of asbestos fiber. As to the appropriate safe concentration, Jackson advises: "as you are aware, I am sure, the threshold limit list of the American Conference of Governmental Industrial Hygienists suggests a limit of 5 million particles per cubic foot for asbestos. Assuming that the airborne dust would approximate the materials ratios of the product, this would indicate that dust levels approaching 50 million particles per cubic foot would not contain an excessive amount of asbestos fiber."

Jackson refers to his earlier letter for appropriate dust control measures. That letter states: ". . . The measures which we employ to control the exposure potential include point of operation ventilation control, vacuum cleaning of work areas and spilled material, the use of U.S. Bureau of Mines respirators for intermittent exposures, job methods to minimize bag breakage and a vigorous program of housekeeping."

Editor's note: J-M's description summarizes a second, correcting letter in which Jackson said Thermobestos was calcium silicate with about 10% asbestos and discussed dust levels up to 50 million particles. That letter is not in this file, which holds only the first letter, the one saying Thermobestos contained expanded perlite.

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