This appears to be the source of black smoke visible in DC today.
WASHINGTON: "DC Fire and EMS extinguished a 2 alarm fire on the roof of 300 7th St. SW., which left two firefighters injured. The fire appeared to be contained to the roofing materials and the roof of a building under construction Thursday morning. The blaze was on the roof of the future headquarters of D.C. Metro according to the Metro Twitter page. One firefighter had a minor injury and was transported to the hospital, according to DC Fire and EMS. A second firefighter sustained non-life-threatening injuries. Twenty units and 100 personnel responded to the fire."
https://www.localdvm.com/news/washington-dc/two-firefighters-injured-after-roof-of-future-headquarters-of-dc-metro-caught-on-fire/