I love these stories! Almost as intriguing as the personal mysteries thread!
I know there have been a few incidences in various neighborhoods I've lived in, but my veryvery favorite ever would be when the high school near my neighborhood had to be shut down and decontaminated.
Why? Because some of the students stole some mercury from the chem lab and went bezerk with it! They shared it with friends, rolled it over their skin, hid it away in pockets, squirted it at each other with water bottles, smeared it on walls. As anyone familiar with the effects of mercury knows, this is inSANE.
So anyway, the faculty didn't realize what was going on until the afternoon, when a student fainted in class. An EMT found the mercury on her and had her tested. Mercury poisoning was deemed the reason for her collapse. Suddenly, teams are in the school, doing tests. The whole building is shut down, with every student forced to stay inside until they could be stripped, decontaminated, tested and sent home in new clothes donated from the Salvation Army. It took hours, as this school held around 2000 students. A few other students were sent to the hospital with severe levels of contamination (can't remember the number, as this was over 10 years ago), and the school was shut down for almost a week while professional cleaners were brought in to decontaminate the school. I think it cost the city quite a pretty penny at the end of the affair. A nearby bowling alley, where the kids hung out for lunch, also had to be decontaminated at the city's expense.
I believe a few days later, mercury was found on one of the sidewalks in the neighborhood. One of the students who instigated the event admitted to bringing mercury home with her, and her house was found to be contaminated. Her parents had to gut it before it was livable, and I think they attempted to sue the school for expenses. Don't remember if they won, though!