None of the prohibitions in § 90.15 shall apply to or be enforced against any police or fire vehicle of the City or ambulance while engaged upon necessary public emergency business; necessary excavations or repairs of bridges, streets, or highways by, or on behalf of the City, county or state during the night, when the public safety, welfare, and convenience renders it impossible to perform such work during the day; the reasonable use of stationary amplifiers or loudspeakers in the course of public addresses which are noncommercial in character.
('88 Code, Title IX, Ch. 109, § 9.22)