Applies to establishments engaged in the manufacture of mineral wool insulation from siliceous materials such as, but not limited to, rock, slag, and glass, or combinations thereof. In a special furnace, hot air or steam is blown through molten rock or slag, shredding the material into a mass of fine intertwined fibers to form the wool. To produce fiberglass insulation material, molten glass is drawn at high speeds through orifices, then subjected to jets of high pressure steam which break the glass filaments into fine fibers. The final product, regardless of raw material, may be shipped in granules which are bagged, or formed into flat sheets, cut to size, enclosed in paper or foil, and packaged. Incidental rock, slag, and glass crushing operations are contemplated by this classification.

This classification excludes the digging or quarrying of raw materials which is to be reported separately in the classification appropriate to the work being performed, and the manufacture of asbestos products which is to be reported separately in classification 3104.