For the purpose of this chapter the following definitions shall apply unless the context clearly indicates or requires a different meaning.
"CIVIL EMERGENCIES."
(1) A riot of unlawful assembly characterized by the use of actual force of violence or any threat to use force if accompanied by immediate power to execute the force by three or more persons acting together without authority of law.
(2) Any natural disaster or man-made calamity including flood, conflagration, cyclone, tornado, earthquake, or explosion within the corporate limits of the city resulting in the death or injury of persons or the destruction of property to such an extent that extraordinary measures must be taken to protect the public health, safety, and welfare.
"CURFEW." A prohibition against any person walking, running, loitering, standing, or motoring upon any alley, street, highway, public property, or vacant premises within the corporate limits of the city during the hours in which a "CURFEW" has been imposed, excepting persons officially designated to duty with reference to the civil emergency.
('75 Code, § 53.21(A))