What about the Explosion? - Figure D18-1: A hole about 18" in diameter in the roof of the concrete room invited speculation and interest until the FBI bulldozed the structure on April 30, within two weeks of the fire. Seven years later, Special Counsel John C. Danforth concluded that the hole was "spalling" from age and heat damage. But the rebar lacks weather corrosion and the concrete is not flaking, as with heat spalling. (Exhibit USAWDTX 086-00897 catalogued by the US Attorney, Western Texas via Michael McNulty via Wikimedia) Image is rotated to fit page. Next →