In the past analyses of aircraft impact against buildings the kinetic energy of fuel of the impacting aircraft was accounted for, but the chemical energy content was not. This paper addresses the explosion problem by means of analysis as well as well as Finite Element simulation. The effect of fuel detonation is evaluated with less than 1% of the aircraft fuel content acting in this manner. The fuel-air mix in the model was placed at one level, between the floor and ceiling of the worst affected impact area. The damage resulting from this is developed and presented herein. A comparison of resilience of the old WTC towers versus the new 1-WTC is made.