M. W. Blackhurst's Final Report on Asbestos for Coal Mine Rock Dusting (1959)

A two-page memorandum of December 15, 1959, from M. W. Blackhurst of Johns-Manville's Research Center, the final report of the "Asbestos Fibre New Uses Program" on mine roof dusting. Coal mines spread about a million tons of limestone dust a year on their walls, roofs and floors so that an explosion would throw the dust into the air and stop the flames from spreading, and J-M hoped asbestos would do the job better. Test applications began in a Pennsylvania mine early in 1955, and after two years the state mine inspector reported that asbestos gave more coverage per ton, raised less dust during spraying and kept its light color longer.

What it shows

Pennsylvania would not approve asbestos without the U.S. Bureau of Mines, because federal law (Public Law 552) limited rock dusting material to 5 percent free and combined silica, and asbestos contains about 40 percent. With the support of the United Mine Workers Union, J-M persuaded the Bureau to test asbestos in its experimental coal mine. Both wet and dry applications caked more than limestone, so the Bureau would not recommend changing the law, and Blackhurst concluded that further spending "would not be justified." A favorable dust count survey had been made by the Industrial Hygiene Foundation of America during the Pennsylvania tests.

In Johns-Manville's chronology

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

In a memorandum dated 12/15/59, M.W. Blackhurst (J-M Research Center) discusses J-M's efforts to promote the use of asbestos alone or combined with limestone for mine roof dusting in the bituminous coal mines of Pennsylvania. Limestone was the traditional material used to coat or dust the walls. roof, and floors of the coal mines to prevent fires from spreading after an explosion. In the event of an explosion, the limestone dust is dispersed from the roof and walls into the air by shock waves and air turbulence where it adulterates any airborne coal dust and absorbs the heat and cools any flames. Due to several undesirable characteristics of limestone, such as poor adhesion to mine walls, low coverage per ton, and relatively poor light reflectance, it was thought that asbestos might perform better.

Testing of asbestos began in 1955, and at the end of two years, it appeared that asbestos had several advantages over limestone. The results were reported to the State of Pennsylvania. Due to a conflict between a Pennsylvania and a federal mining law, which limited rock dusting material to 5% maximum free and combined silica (asbestos contains approximately 40%). Pennsylvania would not approve the use of asbestos until J-M obtained approval from the U.S. Bureau of Mines. The Bureau stated that it would only recommend a change in the law if asbestos applied, either wet or dry, caked less than limestone. Tests performed by the Bureau showed that asbestos caked more than the limestone presently used. Therefore, the Bureau did not recommend a change in the law, and J-M abandoned further promotion of the use of asbestos as a mine roof coating.