Debris from the collapse of WTC 1 located between WTC 7 (left) and the Verizon building (right).
FEMA
2001
<a rel="nofollow" class="external free" href="http://www.fema.gov/pdf/library/fema403_ch5.pdf">http://www.fema.gov/pdf/library/fema403_ch5.pdf</a>