Emergency purchases, without recourse to requisition or purchase procedure, may be made by any department or division head, when such emergency action is necessary. An emergency situation means a situation in which the Purchasing Agent is not available to approve normal purchase procedure and when the nonavailability of such Purchasing Agent to approve any such purchase would adversely affect the best interest and the day-to-day operations of the City. When an emergency purchase is made by any department or division head, a written explanation of such purchase shall be made to the Purchasing Agent of the City within twenty-four hours after such purchase is negotiated or made. The Purchasing Agent and the department or division head shall subsequently prepare and sign a purchase order for the emergency purchase.