Suddenly there was such a violent earthquake that the foundations of the prison were shaken. At once all the prison doors flew open, and everyone's chains came loose. (NIV)
Suddenly there was a great earthquake, so that the very foundations of the prison were shaken; and at once all the doors were opened and everyone's shackles were unfastened. (AMP)
And suddenly there was a great earthquake, so that the foundations of the prison were shaken: and immediately all the doors were opened, and every one's bands were loosed. (KJV)