You are subject to this subpart if you own or operate an industrial, commercial, or institutional boiler or process heater as defined in Sec. 63.7575 that is located at, or is part of, a major source of HAP, except as specified in Sec. 63.7491. For purposes of this subpart, a major source of HAP is as defined in Sec. 63.2, except that for oil and natural gas production facilities, a major source of HAP is as defined in Sec. 63.7575. [78 FR 7162, Jan. 31, 2013]