PHILADELPHIA (CBS) — The side wall of a three story apartment building collapsed Thursday morning in West Philadelphia.

Three tenants inside at the time of the collapse were not injured.

The brick wall on the second and third floors collapsed onto a vacant lot and the sidewalk on Cambridge Street, near 40th Street in Mantua shortly after 11 a.m.

“I was just sitting in my truck, listening to the radio,” says Alphonso Asber. “I just a heard a loud kaboom, like it was a gas explosion or something. The vibration sort of shook the truck a little bit.”

“It was a big noise and kind of dust and stuff came up,” says Darren Ross, who was home in bed in his second floor apartment. “(It) basically shook me out of bed.”

The collapse allowed a clear view into the apartments where a sink with water shooting out could be seen by onlookers outside.

Fortunately, the floors and the the rest of the structure held, and the residents were able to get out safely.

Authorities are investigating the cause of the collapse.