There were a few U.S. makers that used an asbestos board, with General Fireproofing of Youngstown , Ohio being a big user of this type protection. I have seen one Mosler safe that used this type of board. Most U.S. makers used a poured type of fire protection making it more difficult to tell what is in it. I don’t think it was commonly used in the 1800’s, more common in the period between WWI and WWII, when the goal was to lighten the weight of fire safes that were widely used in office buildings. What surprised me though, was that it was listed as an ingredient in Meilinks poured mix, according to one of their early pre- WWI catalogs. So it appears that it was more commonly used than I previously had thought.
