Communication fell when the two planes hit the Twin Towers
The higher-ups in the buildings told everyone to go back to work after the first tower was hit.
Communication was fallen on 9/ 11 because the people and officials didn't expect another plane to hit.
After the first tower was hit, everyone at the WTC were told to go back to work. Even though the people were confused, they cooperated. That order saved hundreds of people's lives. When the second plane hit the second tower, everyone who was in the WTC survived, and if they didn't, they died or got cancer from all the debris outside.