You should cover any opening from the room. This includes a dryer vent if there is a washer/dryer located in your shelter-in-place room.
FEMA Common FAQ
No, you do not need to disconnect water lines. However, you should make sure that the area where the pipe comes through the wall is properly sealed to eliminate airflow with an appropriate sealant such as caulk.
If the plume passed over your house there is a potential for contamination, especially to fabrics, carpets, and other materials, although it is unlikely to pose a significant threat. Local officials will advise you if your house is safe and what actions to take after a chemical emergency.
Unless there was contamination by a liquid form of the chemical, objects in or out of the house should not pose a significant health risk, however one should take precaution and not touch or handle items or surfaces that were potentially exposed to the vapor cloud, especially outside the house.
The best room is the room with the fewest windows and doors. Since each opening will require time to seal it off, minimizing the number that you will need to seal will shorten the time it takes to reduce airflow into the room. The room should be easy to get to and provide adequate space for family members.
Several vendors produce solar powered and hand crank weather radios that offer additional features like the ability to charge one's mobile phone or provide light like a flashlight. No standards currently exist for these products, the only recommendations the federal government can provide is to research each product and purchase the one you feel most meets your needs.
Individuals should precut plastic to fit over the entire openings of windows and doors, including the frames. In addition, plastic should be cut to cover vents and ventilation fans. Cut the plastic a minimum of 6" wider than the opening. This will make it easier to put up the sheets if needed.
DHS recommends using duct tape with a minimum thickness of 10 mil (0.01 in). DHS does not recommend particular brands.
Emergency officials would likely advise individuals to shelter-in-place when the chemical is expected to dissipate in a short time period, there is not time to evacuate, or chemical fumes could quickly overtake you if you do not seek shelter immediately.
Disasters can sometimes make it unsafe for people to leave their residence for a period after the disaster hits. The need for long-term sheltering-in-place, e.g. having a three-day supply of food and water, is important for families preparing for emergencies where supplies to stores, electricity and water are disrupted.