A nuclear power plant accident, a nuclear explosion or a dirty bomb are examples of radiation emergencies. If something like this happens, you may be asked to get inside a building and take shelter for a period of time instead of leaving. The walls of your home can block much of the harmful radiation. Because radioactive materials become weaker over time, staying inside for at least 24 hours can protect you and your family until it is safe to leave the area. Getting inside of a building and staying there is called "sheltering in place."