No person will allow sulfur oxides to be emitted from any existing fossil fuel burning equipment in excess of two and one half (2.5) pounds per million BTU input, maximum 2-hour average. For purposes of these regulations, "existing fossil fuel burning equipment" means equipment, machines, devices, articles, contrivances, or installations in operation prior to February 26, 1974; and, the heat input will be the aggregate heat content of all fuels whose products of combustion pass through a stack, or the equipment manufacturer's or designer's guaranteed maximum input, whichever is greater.
129 Neb. Admin. Code, ch. 16, § 001