The Arlington County Fire Department (ACFD) retains control for 10 days, relinquishing it on September 21 to the FBI after the fire was officially declared extinguished.1

1 Goldberg, A. Papadopoulous, S., et al “Pentagon 9/11” Historical Office, Office of the Secretary of Defense n.d PDF. March 17, 2011 page 85 http://osdhistory.defense.gov/docs/Pentagon%209-11.pdf