On April 19, 1995 a 4,800-pound bomb, concealed in a rented truck, exploded 20 feet from the Alfred P. Murrah Federal Building in downtown Oklahoma City. The explosion and partial collapse of the nine-story building killed 168 people and injured several hundreds more.
Exponent engineers were called to the site to assist in the rescue effort and determine how to safely remove debris from the remaining structure. Structural engineers conducted on-site research to verify concepts used in designing blast resistant buildings and form the basis of a set of design principles called "defensive architecture" to minimize the loss of lives and property in the future. Finally, to test the fertilizer alleged to have been used in the explosion, Exponent detonated a series of test bombs in the Arizona desert to investigate any potential explosive properties.
Reza A, McCarthy RL. Measurements to determine the effect of selected additives on the detonability of ANFO mixtures. 25th Annual Conference on Explosives and Blasting Techniques, International Society of Explosives Engineers, February 1999.