The Chief of the Fire Department, with the approval of the Mayor, shall have power to modify any of the provisions of the Fire Prevention Code and the Life Safety Code 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 Fire Chief and Mayor thereon shall be entered upon the records of the Mayor, and a signed copy shall be furnished the applicant. (1984 Code)