Whenever the mayor determines that there has been either an act of violence or resistance to a lawful exercise of public authority, and that as a result thereof, there is reason to believe that there exists a clear and present danger of a riot or other general public disorder involving widespread disobedience of the law and substantial injury to persons or property, which riot or other general public disorder constitutes an immediate threat to the public peace and to the general welfare of the city, or any area of it, the mayor may declare a state of civil disorder within the city or any of its areas. (2000 Code § 38.01)