The Chairperson of the City Planning Commission may modify the general requirements of the public access areas listed in Section 93-73 (Public Access Areas on the Ninth Avenue Rail Yard), provided that the Chairperson certifies to the Commissioner of Buildings that such a change is necessary to accommodate unforeseen ventilation demands within the Ninth Avenue Rail Yard. In addition to the site plan required pursuant to Section 93-732 (Certification for public access areas on the Ninth Avenue Rail Yard), a mechanical plan shall be provided demonstrating the need to modify such general requirements.