40 C.F.R. § 424.20
The provisions of this subpart are applicable to discharges resulting from the smelting of ferroalloys in covered electric furnaces or other smelting operations, not elsewhere included in this part, with wet air pollution control devices. This subcategory includes those electric furnaces of such construction or configuration (known as covered, closed, sealed, semi-covered or semi-closed furnaces) that the furnace off-gases are not burned prior to collection and cleaning, and which off-gases are cleaned after collection in a wet air pollution control device such as a scrubber, 'wet' baghouse, etc. This subcategory also includes those non- electric furnace smelting operations, such as exothermic ( i.e. , aluminothermic or silicothermic) smelting, ferromanganese refining, etc., where these are controlled for air pollution by wet air pollution control devices. This subcategory does not include noncontact cooling water or those furnaces which utilize dry dust collection techniques, such as dry baghouses.
40 C.F.R. § 424.20