Whenever a civil emergency, or the imminent threat thereof, occurs in the city and results in, or threatens to result in the death or injury of persons or the destruction of or damage to property to such extent as to require, in the judgment of the mayor, extraordinary measures to protect the public peace, safety and welfare, the mayor shall forthwith proclaim in writing the existence of a civil emergency. In the absence of the mayor, such a civil emergency may be declared by the mayor pro tem, and in the absence of the mayor pro tem, by the city administrator. For purposes of this chapter a civil emergency shall mean: