All trenches in public streets and alleys shall be properly protected at night with a substantial barricade at least three feet (3') high, the same to have the contractor's name and telephone number printed thereon; and an amber light shall be placed at each end of the trench (in cases where the trench is 10 feet or more in length) or obstruction, in such position as to shed its light upon said excavation or obstruction; and the same shall be kept brightly burning from sunset to sunrise. The chief of the fire department and chief of police shall be notified of such obstruction prior to dark of the same day it is put up. (2001 Code § 150.105)