Manufacturing and industrial processes in an I-L zone shall use only gas or electricity as a fuel; provided, however, that oil burning equipment may be installed for standby purposes only. (Ord. 3153 § 2 (Exh. A), 2010; Ord. 1281 § 1, 1970; Ord. 1212 § 1, 1969; prior code § 33.513 (I)(2)).