The chief of the fire department shall have power to modify any of the provisions of the code hereby adopted in his own discretion or 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 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 modifications when granted or allowed and the decision of the chief of the fire department thereon shall be entered upon the records of the department and for applications requesting change, a signed copy shall be furnished the applicant.