An ongoing chemical disaster in Belgium is getting people worried. Each day a train loaded with acrylonitrile makes a journey from the Dutch port of Rotterdam to the Belgian city of Ghent and its port. On May 4 one of those trains derailed (cause: overspeeding) just outside the Belgian town of Wetteren and caught fire (NOS News BBC News). This fire was quickly dealt with but the disaster had yet to start.
Large amounts of acrylonitrile together with partial-combustion product hydrogen cyanide made it's way into the town's sewage system partly due to the use of water in the fire fighting operation. But then toxic fumes made it back up into local houses causing the death of one resident and his dog. Ironically in the event of chemical disasters, authorities (in this part of the world) advise and expect residents to stay indoors with the windows shut.
Now three days later lethal concentrations of hydrogen cyanide still come up from the sewer and a large evacuation is anticipated (De Morgen). The arrival of rain does not help.
Update 08-05-2013: Evacuation not needed after all.