Section 3-104. Declaration of emergency

Whenever the mayor determines that
  there has been an act of violence or a flagrant and substantial defiance
  of or resistance to a lawful exercise of  public  authority,  and  that,
  partly  on account thereof, there is reason to believe that there exists
  a clear and present danger of a riot or other general  public  disorder,
  widespread disobedience of the law, and substantial injury to persons or
  to  property, all of which constitutes a threat to public peace or order
  and to the general welfare of the city or a part or parts  thereof,  the
  mayor  may  declare  that a state of emergency exists within the city or
  any part of parts thereof.