Emergency officials say an explosion causes thousands of dollars in damages at Northern Asphalt In Green Bay.  The Green Bay Metro Fire Department says crews responded to an explosion shortly after 4:30P-M Monday. Firefighters arrived to find debris littering the road and parking lot around a conveyor belt feeding into a distribution silo. The covers on the conveyor were burning.  Fire officials say plant employees attempted to keep the flames down fire extinguishers until the firefighters arrived, and then helped firefighters remove the burning covers. Fire department didn’t detail the cause of the explosion but said it happened from the processing of asphalt. Damage is estimated at $30,000. Firefighters were on the scene for almost four hours. No injuries were reported.