From a post:

Interestingly, the Wikipediaentry already notes the fire, and a potential cause:
On December 19, 2007 the building was hit by a fire, leading to its evacuation. According to the Fire Department of the District of Columbia, the fire is believed to have begun on the third floor in either a telephone bank area or electrical closet. Hmmm… telephone bank area??? Perhaps the circuits are burning up with the telecom spying on Americans. Or perhaps the paper shredders, which have been churning on overtime since the Bush Administration came into office, overheated???