Portsmouth Polytechnic Psychology Department did some research for 45/1992: Human Behaviour in Fires commissioned by the ODPM and they found a similar situation.
People tend not react to the fire alarm until somebody makes move or they receive verbal instructions. They found people who are trained were usually the first to react, on one occasion it was a nurse who showed much concern but did not move for at least 5 minutes.
Following on from twsutton's post, I have also been told about research that indicates that people respond far better to verbal explanations and instructions than to warning tone signals. This seems to apply more to people in public areas rather than those in buildings who have been given repeated training in what to do when a warning tone signal is given. Evidently, only automatic voice alarms are used on fire alarm systems in Australia.
I cannot understand why voice message alarm sounders are not more porpular in this country. All the major manufacturers produce them.
Finally, why is there a warning tone system installed in a public building holding a 1000 people? Surely, this is exactly the type of building that should have a staff alarm and staff who are properly trained to ascertain the level of threat of the fire alarm warning and carry out an orderly evacuation procedure, as necessary?