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PHILADELPHIA (CBS) — A powerful explosion rocks an apartment building in West Philadelphia. It happened around 11 p.m. at the Sheldrake Apartments on 49th and Spruce Streets.

Police say a 56-year-old man mixed gun powder and dynamite, causing the explosion.

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Twenty people were evacuated and placed on a SEPTA bus to stay warm during the investigation.

A neighbor says he thought the loud noise came from a gas explosion.

“We go out and the cops are coming out here and dragging a guy out. I saw the blood in his face and his arm. I was asking the officer and he said he was making some time of explosion,” the neighbor explains.

Credit: CBS3

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“And that shocked me because we were expecting, like, to be a bomb. We were thinking it would be the gas,” the man adds.

The suspect is now being treated for minor injuries.

Residents have returned to their apartments.