Pittsburgh police have reopened Grant Street to one lane after it was closed to traffic in Downtown Pittsburgh as at least two manhole covers along the thoroughfare popped loose, one with a thunderous boom, around noon Tuesday. The cause was traced to a fire affecting high voltage wires under Grant Street, according to Emily Bourne, a police spokeswoman. Pressure built up beneath the street and dislodged the manhole covers, she said. People could feel the initial blast a block away at the Allegheny County Courthouse. No one was injured, according to Public Safety Director Lee Schmidt.