At around 10:30 pm, on February 11th, 1998, the Chicago Fire Dept. arrived at a tire service center after receiving a call stating that fire was seen in the interior of the building. No fire was visible from the outside of the structure which consist of a showroom and a service area. The First Firefighters that entered the building reported an odor of a burning car and saw black smoke at the ceiling space of the service area. Other firefighters at the rear of the building reported that the windows were dark and smoky, they knew there was a smoldering fire somewhere in the building. On the roof of the building ventilation holes were cut and it was reported that smoke began to emit followed by flames. The building had an unfinished area below the roof where tires and other combustible items were stored (later believed to be the origin of the fire). At around 10:45 pm and while nine firefighters were inside the building bumping into each other due to poor visibility, the hot gases that accumulated at the ceiling ignited creating a phenomenon called "Backdraft." The explosion caused a pressure wave that disoriented & knocked the firefighters to the floor. In addition, molten Polystyrene that was used for insulation began to fall from the ceiling on the confused firefighters. Most of the firefighters managed to escape the building, later however, the headcount revealed that two firefighters were missing, a Backdraft is defined as an explosion resulting from the sudden introduction of oxygen into a ventilation-limited space containing unburned fuel and gases, in other words the fire consumed most of the air in the compartment which knocked-down the flames, however hot gases still existed in the compartment until air was re-introduced suddenly which allowed the fire to re-ignite in an explosive manner. In this case it was estimated that the sudden introduction of air to the unburned gases inside the building came when the service area garage was self-activated and opened. Two firefighters died that night and three others were injured. Here are some indication of Backdraft published on FEMA page: 

1. Black smoke becoming dense & greyish without visible flames.

2. A well-sealed building might indicate air confinement & excessive heat buildup.

3. High concentrations of flammable CO gas could be present due to incomplete combustion. 4. Little or no visible flame or flames in smoke exiting the structure, especially in eaves of the structure. 

5. Smoke leaves the building in puffs and being drawn back in. Fire is trying to find oxygen, and this is the appearance of smoke pulling in under doors or through cracks.

6. Smoky windows, brown in color, with visible cracking & rattling. 7. Sudden movement of air and smoke inward when an opening is made.

Video shows a Backdraft situation during a fire in NY City.