Excerpts from the ChicagoTribune.com:

Four firefighters were burned in a backdraft that erupted during a blaze Sunday afternoon in the 4900 block of West Potomac Avenue in the city’s Austin neighborhood on the West Side. They were taken to Stroger Hospital, where their conditions have stabilized, according to the fire department.

The four firefighters suffered first and second-degree burns after flames suddenly intensified, forcing some to jump from a second-story window.

Chicago Fire Department Commissioner Jose Santiago said firefighters tracked the source of the fire near a kitchen on the second floor. As they entered into that area, the heat and size of the fire surged forcing them to retreat.

“As the firefighters make entry, you may have a fire just sitting there, and the only thing it’s lacking is oxygen,” he said. “In order for firefighters to get in there, they’re going to open doors, and it will start feeding that fire. Sometimes, it’s like an explosion. They’re engulfed in fire. They all had their masks on. That’s why they’re alive right now,” Santiago said.

Santiago said some firefighters had trouble with their water supply as they were inside the building. It was not clear what caused the issue, but Santiago said that and the cause of the fire are under investigation.

“Anything can happen. A hose kinks, a hose can get stuck underneath a door,” he said. “They’ll take a look at all that and try to figure out why they had the problem.”

A mayday was called when the backdraft occurred as firefighters were searching for victims and putting out the fire on the second floor. An EMS Plan I, sending six ambulances to the scene, was also initiated.

The first calls of the blaze came in at 12:04 p.m., and the first responding firefighters got there at 12:08 p.m. The mayday was called at 12:20 p.m.