PHILADELPHIA (AP) — Authorities say a man injured in an explosion inside a Philadelphia apartment has been charged with causing the blast.

The explosion blew out the windows of the first-floor apartment around 11:30 p.m. Saturday and left the 56-year-old man with cuts on his face. He remained hospitalized Sunday, but his name and further details on his injuries have not been released.

Authorities say the explosion occurred because the man mixed gunpowder with dynamite. It’s not clear why he was doing that or what charges he might face.

No other injuries were reported in the blast. But roughly 20 other building residents were evacuated for about 90 minutes while a police bomb squad investigated.