Damaged Insulation Led To Underground Explosions In Columbus

American Electric Power says explosions that sent manhole covers flying in downtown Columbus last February happened when insulation material on electricity cables broke down because of water, salt and other factors. Nobody was injured in the explosions that sent two manhole covers into the air and shattered one. The utility is spending around $30 million to prevent any similar explosions. AEP says the cracked insulation exposed metal wires to the air and the high level of electricity running through the cables produced heat. That caused the rubber insulation to burn, releasing a flammable gas. The utility says the gas built up inside a small vault that holds electricity equipment and the heat and electricity likely led to a spark that caused the explosion.