At approximately 2115 hrs Engine 511 was dispatched to Manassas Mall for an Investigation. The additional dispatch information advised that a sprinkler had activated at the H&M store. Upon arrival at the store the smell of burning material was noticed and once inside the store a haze of smoke could be seen in the back of the store. Engine 511 Officer called Prince William Communications and requested that they fill the box for a commercial structure fire. That request brought additional fire department units from Nokesville, City of Manassas, Yorkshire, and Lake Jackson. Battalion Chief 501 (Chief Wood) was in the area and quickly arrived on scene and established Manassas Mall Command. Engine 511's crew encountered a heavy amount of smoke in the dressing room area of the store as well as an actively flowing sprinkler head. A search of the area with a thermal imaging camera (TIC) found no heat in the area. An even more thorough search found that there had been a fire behind a mirror in a dressing room underneath the active sprinkler head.

Once it was determined that the fire was out the sprinkler system was able to be turned off and Command started to release units from the scene. However, there was still a significant amount of smoke in the store. All of the fans from Tower 525, Tower 501, and Rescue 521 just were not enough to clear the smoke from the store. Command requested the Mass Ventilation Unit from fire station 514 in Lake Ridge. Once MVU 514 with its crew from Engine 514 arrived, set up, and started blowing the smoke was gone within minutes.

The Duty Fire Marshall (FM 515) then responded to the scene to conduct an investigation. It did not take long to determine that the cause of the fire came from the light fixture behind the mirror in the dressing room and that the sprinkler extinguished the fire before it could get out of control. According to an article posted to InsideNOVA.com "the store will be closed for an undetermined amount of time" probably due to the damage caused by the smoke and large amounts of water released from the sprinkler.

All fire department units were finally clear from the scene just after midnight.

http://www.insidenova.com/news/prince_william/local/manassas/cause-determined-in-fire-at-manassas-mall-on-friday/article_433a6b9a-d775-11e7-a673-938151534c0c.html