"Caution--Use Asbestos"

According to the 1971 World Book Encyclopedia's entry on "Asbestos", asbestos could be obtained from open pit mining (Vermont and Quebec) using power shovels, or in underground mining where the broken rock had to be "cobbed" (hand sorted) into different grades.  The biggest producer was Quebec, with 40 percent of total world production.  Products include firemen's suits, gloves, helmets, theatre curtains, awnings, conveyor belts for hot materials, roofing shingles, wallboard, tiling, and electrical insulation.  No mention in the entry on any health hazards, although these had been observed and documented since the 1920's.

The World Book Encyclopedia.  Chicago:  Field Enterprises Educational Corporation, 1971.