(CBS) – Four Chicago firefighters were injured Thursday when a staircase collapsed under them at a bungalow fire on the Far Northwest Side.

The firefighters were in good condition, despite having to be rescued from the basement of a burning bungalow at 5718 N. Newark Av. in the Old Norwood neighborhood.

Five firefighters were trying to determine if anyone was trapped or overcome in the burning bungalow when the home’s stairs collapsed under them.

“They started to go up a staircase to go ahead and fight the rest of the fire, which had moved its way up to the second floor,” said Fire Commissioner Jose Santiago. “As the firefighters were moving up the stairwell came loose. Thus, all the firefighters fell down into the basement.”

A mayday (distress) call was then issued, which brought 40 units and 120 firefighters to the scene. Four of the five firefighters who fell into the basement were hospitalized, but were in good condition at Resurrection Hospital.

“These injuries are basically ankles, backs, some of them hit their heads on the way down,” Santiago said. “Helmets were knocked off.”

Santiago said that within minutes, firefighters were able to determine that no one else was inside the two-story bungalow.

The cause of the fire was under investigation.

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