Nothing contained in this chapter shall be construed to prevent any person maintaining any pipe or conduit, in any street, alley or other public place, by virtue of any law, ordinance or permit, from making such excavation as may be necessary for the preservation of life or property when such necessity arises during such hours as the offices of the city are closed; provided that the person making such excavation shall obtain a permit therefor within four hours after the offices of the city are first opened subsequent to the making of such excavation.
(`83 Code, § 12.08.160)