The operator of any tank vehicle delivering petroleum products within the city shall remain at the control valve of such vehicle while such products are being discharged therefrom and shall exercise the control necessary to prevent overflowing, spills, or other similar accidents. A dead-man valve shall be required on all tank vehicles, and it is unlawful to block open the valve so as to make the dead-man feature inoperative. (Ord. 3209 §4, 1965).