|To our knowledge, none of the [fire] chiefs present believed that a total collapse of either tower was possible. [9/11 Commission Report]
The OEM Issued a
WTC Collapse Warning
Why didn't the 9/11 Commission mention this?
It seems logical that the Office of Emergency Management would warn their boss of the impending collapses, so this would explain how Mayor Giuliani received warning of the collapses.
How did the OEM know something that firefighters in WTC 2's impact area didn't?
Why weren't all firefighters warned?
Number of firefighters and paramedics killed: 343. Number of NYPD officers: 23. [nymag.com]
There would have been a severe lack of law enforcement officials in New York in the immediate aftermath of 9/11 if they hadn't received a five minute warning. Think about it.
Received a Two Hour Warning of the 9/11 Attacks
The 9/11 WTC Collapses: An Audio-Video Analysis
What Really Happened