Public safety is declared to require that the uninterrupted operation of certain industries essential to national defense, such as the aircraft manufacturing industry, and of companies or agencies supplying water, gas, electric and other essential services, be protected by preventing the intrusion upon the properties thereof of idle, curious or malicious persons and of persons whose presence thereon is not necessary, and by prohibiting the loitering about such places by persons capable of inflicting harm or of impeding the operation conducted thereon. (Prior code § 10.45.010)