The chief of the fire department shall have power to modify any of the provisions of the Fire Prevention 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 Fire Prevention Code; provided, that the spirit of the Fire Prevention 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 chief of the fire department thereon shall be entered upon the records of the department. One signed copy of the decision of the chief of the fire department shall be furnished the applicant, and one signed copy shall be filed in the office of the clerk. [Code 1975 § 2.2-2.09.]