Two explosions were heard inside. One firefighter was injured in the blaze fight. Several people were forced to evacuate their homes.
The building has to come down. But first, crews from several city departments have work to do to minimize damage from the fire to neighboring homes.
"There was a strong west wind. Somehow it gets in there even through the[re are] storm windows," said Don Lee.
Smoke is one nuisance you can wait out. Another - more damaging - element is impacting several area homes.
"There are concerns about water. There's high levels of water in the street. And we have a couple of residences that have flooding that we're trying to attend to right now," said Assistant Deputy Fire Commissioner, Mark Nielsen.
Annabel Salazar and her family live right next to the burning building.
"They had us evacuate the building because there was too much smoke upstairs. It was pretty scary," she said.
It wasn't until later they noticed damage from water, not fire or heat.
"All that water that was being ran through the hose started flooding the basement at about 4:30 a.m.," said Salazar.
City water crews were diverting water into storm drains. That seems to be working. Next up - the building department will come to determine how the building will come down.
Firefighters responded to the 2-11 blaze at Air Control Inc., 2917 W. Irving Park Rd., about 3:20 a.m., according to Fire Media Affairs.
A hazmat response was called to the blaze, according to Fire Media.
The fire was extinguished by 5:35 a.m., though firefighters were still chasing hot spots as of 6 a.m., according to Fire Media.
CTA No. 80 Irving Park buses were temporarily rerouted, according to a CTA alert.
The Sun-Times Media Wire contributed to this report.