Engine 21 was parked under the north pedestrian bridge that crossed West Street from the WTC to the World Financial Center complex on the river. Neither of the two bridges survived the collapses, but the north bridge was completely destroyed, being almost immediately west of Tower One. The bridge destroyed the cab of E21 but spared the back. Many firefighters dove under trucks that day to save their lives. For some it worked; for others it was no refuge.
“Rounding one corner, a visitor will suddenly come upon the rear end of Engine 21 (“Keep back 200 feet,” it still commands), looking merely like an old fire truck that has seen a lot of action. A few steps more into the gallery, however, and it is revealed as a mechanical carcass.” www.nytimes.com/2013/06/29/nyregion/at-9-11-museum-shocks-of-awe-and-grief.html