Known as taking shelter-in-place, you will want to have a safe environment in your home where you can go when you find yourself in immediate danger. An effective shelter is important if the air around you becomes contaminated with a dangerous agent, such as a chemical or biological attack, or a hazardous materials spill or accident.
To create a shelter, choose a room as far removed from the outside air as possible. You will benefit from choosing a room that has few, if any, windows and a limited number of doors.
Once your shelter location is chosen, make it known to each family member and stock it with as many supplies as possible, including plastic sheeting and duct tape that can be used to seal the room. If you are unable to keep your 3-day kit in your designated shelter, place it in a nearby location that can be quickly accessed.
Check your shelter for places where contaminated air could seep through. These include fireplaces, forced air heating systems and dryer vents. Make sure each family member knows how to restrict airflow from these locations
More information is available at Ready.gov