I saw a documentary last year and it was claimed that 20,000 were evacuated from the towers before they fell. Have no idea if that number is correct, but obviously the death toll would have been multiplied by some factor if not for the heroics of the fire dept., police dept. and other individuals.
I remember someone saying that if the planes were to have impacted lower towards the ground floors, nearly everyone in those buildings would have been murdered.
one of the individuals responsible for savings lives:
http://www.freerepublic.com/focus/keyword?k=rickrescorla
IIRC, Rescorla was the last man out of the Towers when the terrorists made
their first attempt.
And was on duty 9-11 to cover for a colleague attending a marriage ceremony.
I remember, vividly, watching TV on 9-11, sick to my stomach as they were warning us that the death toll might be ten to twenty thousand.