Columbus police say a fire in an underground vault belonging to Columbus-based American Electric Power caused several underground explosions downtown early this morning. The blasts knocked off manhole covers, set off fire alarms, knocked out traffic signals and caused several power outages.The vault is near the Renaissance and Chase buildings. The cause of the fire is under investigation. The outages affected several downtown buildings. Police closed East Broad Street between Third and Fourth Streets, North Fourth Street between Broad and Gay Streets, and Lynn and Pearl alleys to investigate. It's not known when the roads will be reopened.