Nuclear and radiological shelter-in-place

Any sturdy building reduces exposure significantly

Ready.gov's radiation guidance is specific about which buildings provide the most protection: brick or concrete structures, basements, and the innermost rooms of large multistory buildings. The physics is straightforward. Dense building materials absorb radiation. More walls and mass between you and the outside equals less exposure.

But Ready.gov also states that any protection is better than none. If the only option is a wood-frame house, get inside it. The EPA confirms that even ordinary building walls block a meaningful fraction of the radiation from a nuclear or radiological event outside.

Move to the innermost room, away from outer walls and the roof. Outer walls and the roof receive the highest direct exposure. The basement or the center of an upper floor provides maximum shielding. Close all windows and doors. Close the fireplace damper. Turn off fans, air conditioners, and any HVAC system that draws in outside air. These are the pathways for contaminated air and particles to enter.

Ready.gov notes that sheltering usually lasts at least 24 hours. Most fallout from a nuclear detonation decays to a fraction of its initial level within 24 to 48 hours. Radiation levels decrease with time as you shelter in place, which is why staying inside is often more protective than leaving.

Why evacuation by car is often the wrong call

The instinct to drive away from a nuclear or radiological incident is understandable. It is also often the more dangerous option. Ready.gov states directly that driving exposes you to contaminated air. A car provides little shielding from radiation. If the roads are congested, and they will be, you sit in a car breathing outside air for far longer than a sheltered household does.

The EPA adds that radioactive materials become weaker over time, and staying inside for at least 24 hours can protect you and your family until officials determine it is safe to leave. The benefit of shelter compounds with time as radiation levels decrease.

CDC advises that if you have loved ones in schools, daycare facilities, hospitals, or nursing homes, stay where you are. Going outside to retrieve them exposes both you and them to radiation. These facilities have emergency plans and will be instructed to shelter in place until it is safe to move people. Family reunification happens after shelter, not during it.

Food and water inside the building before the event are safe to eat and drink. Sealed containers that were outside can be wiped down with a damp cloth before opening. Do not consume food from a garden or anything that was outdoors and uncovered until officials confirm it is safe.

Battery radio, outer clothing, soap and water

A battery-powered or hand-crank radio is the most reliable information source during a nuclear or radiological emergency. Cell phone networks can fail or become overloaded. Television requires electricity. A NOAA weather radio receives emergency broadcasts without depending on either. Ready.gov recommends having one as part of basic household preparedness. During the event, it is how you receive evacuation orders, shelter timelines, and food and water safety guidance.

If you were outside during the initial event or during fallout, decontaminate as soon as you get inside. CDC's guidance: remove the outer layer of clothing before entering the building and place it in a sealed plastic bag away from people and pets. Removing your outer layer of clothing alone can eliminate up to 90 percent of contamination. Shower with soap and water, washing hair with shampoo but not conditioner. Conditioner causes radioactive particles to adhere to hair. Do not scrub skin aggressively; gentle washing is sufficient.

Wait for official instructions before evacuating. Ready.gov states that officials consider wind direction, radiation levels, road safety, and the extent of the incident before advising evacuation. They will specify the route and destination. An uncoordinated self-evacuation can move people toward higher-contamination areas rather than away from them.