Fire evacuation signals:

Members of the public are known not to respond positively to fire evacuation signals. People will often try to ignore the signal and will try to carry on with what they were doing.  Sometimes they won't even recognise the alarm signal.  Voice alarms are very common in shopping malls and other buildings where a large number of the public can be found.  But people often require an additional instruction, directly from a member of staff, to confirm to them that they must leave what they are doing and evacuate the building.

Staff in public buildings, therefore, mostly do not evacuate on hearing the alarm but, rather, have some function to perform which could be, for example, opening the fire doors at the rear of a shop and getting people in the vicinity to use it, or assisting someone in a wheelchair down some steps, or co-ordinating the evacuation from a control room, or moving people who have evacuated away from the area just outside the main exit (where the fire service will soon be arriving).