The Asiana 214 evacuation was initiated by a flight attendant. The evacuation did not commence until 90 seconds after the crash - most likely the FA's were waiting for a cockpit command. Pure conjecture, but I imagine had the FA's waited for the cockpit to command an evacuation, more passengers would have died.
While our FA's may initiate an evacuation, I am unaware of any evacuation at our company which was FA initiated. Also as others have stated, a FA can command an evacuation without using the alarm system.