40 C.F.R. § 424.10
The provisions of this subpart are applicable to discharges resulting from the smelting of ferroalloys in open electric furnaces with wet air pollution control devices. This subcategory includes those electric furnaces of such construction or configuration that the furnace off-gases are burned above the furnace charge level by air drawn into the system. After combustion the gases are cleaned in a wet air pollution control device, such as a scrubber, an electrostatic precipitator with water or other aqueous sprays, etc. The provisions of this subpart are not applicable to noncontact cooling water or to those electric furnaces which are covered, closed, sealed, or semi-covered and in which the furnace off-gases are not burned prior to collection (regulated in subpart B of this part).
40 C.F.R. § 424.10