The county engineer shall make written requisition to the county purchasing agent for all materials, machinery, equipment, and necessary supplies needed for the construction, maintenance, or repair of the public roads, bridges, and ferries of Coffee County. Such requisitions shall be filed and presented by the chairman to the commission at its next meeting, for the approval of the commission. Provided, however, that the county purchasing agent shall have full power and authority to make purchases without first obtaining the approval of the Coffee County Commission if the delay caused by the hereinabove procedure, might, in his or her judgment, cause an unnecessary and harmful interruption in the operation of the county road system, providing the purchases are made in accordance with prevailing law. The county purchasing agent shall be solely responsible and accountable for purchasing the materials, machinery, equipment, and supplies under the approved requisitions, and shall report monthly to the Coffee County Commission.