Just before 4:00pm on Saturday units from Ashburn Volunteer Fire Rescue Department, Sterling Volunteer Fire Department, Fairfax County Fire and Rescue Department, and Sterling Volunteer Rescue Squad were alerted for a fire at Dulles Town Center. A Loudoun County Fire Marshal was already in the mall at the time of the call and located light smoke in one of the stores. Engine 624 arrived quickly and began the investigation, joined by Engines 622, 606, and Truck 606. Battalion 601 arrived and established command. Engine 618 investigated a neighboring store, while Engine 611 established the Initial RIT and Tower 611 checked the roof for possible HVAC issues. The source was determined to be a ceiling HVAC unit and there were no further hazards. Most of the units were released while a few remained to assist with smoke removal.