The Fire Chief has the power to modify any of the provisions of the Code herein adopted upon application in writing by the owner or lessee, or his duly authorized agent, where 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 thereon shall be entered upon the records of the Fire Division and a signed copy shall be furnished the applicant.