The City Manager or his authorized representative shall have the power to modify any of the provisions of the Life Safety Code hereby adopted upon application in writing by the owner or lessee, or his duly authorized agent, when there are practical difficulties in the way of carrying out the strict letter of the Code, provided that the spirit of the Code shall be observed, public safety secured and substantial justice done. The particulars of such modification, when granted or allowed, and the decision of the City Manager or his authorized representative thereon, shall be entered upon the records of the Fire Division and a signed copy shall be furnished the applicant.