During the sound system tests there was a sound like a flock of geese had been inadvertently trapped in the building during construction (or using a more current analogy, something that sounded just like the Martians in the movie Mars Attacks).

What they found was that only 5% of the surviving tenants surveyed had heard the messages from the PA system, and of those people only 50% of them understood that they were to stay in their apartments, while 40% heard the messages but could not understand it.