In addition to other required inspections, the commissioner may make or require inspections of existing buildings, structures, signs, service equipment installations and construction machinery and equipment to ascertain compliance with the provisions of this code and other laws that are enforced by the department. Such inspections may be made on behalf of the department by officers and employees of the department and other city departments and governmental agencies; and by approved agencies, special inspectors or other persons when the commissioner is satisfied as to their qualifications and reliability. The commissioner may accept inspection and test reports from persons authorized by this code or by the commissioner to perform such inspections. Such reports shall be filed with the department.