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If a nuclear weapon is ever used on or near a U.S. city, the steps that save the most lives are simple, and they are the same ones the federal government teaches: get inside, stay inside, and stay tuned. This page turns that guidance into a household plan. It covers what to do in the first minutes, where to shelter wherever you are, how to clean off fallout, what potassium iodide does and doesn’t do, and a card you can print and keep with your emergency supplies.
Short version: If you’re warned, or see a detonation, get into the nearest sturdy building, away from windows. Go to a basement or the center of the building. According to Ready.gov, you’ll have roughly 10 minutes or more before fallout arrives. Stay in the most protected spot for at least 24 hours unless officials tell you otherwise or fire, a gas leak or collapse forces you out. Listen to a battery or hand-crank radio for instructions. When you’re safely inside, take off your outer layer of clothing and wash.
The first minutes: what to do right away
- Get inside immediately. Ready.gov says that if you are warned of a radiation hazard, you should “immediately get inside” and move away from windows. Put as many walls as possible between you and the outdoors.
- If you’re outdoors when a detonation happens and have any warning, take cover behind anything that might protect you. Lie face down to protect exposed skin from heat and debris. When the shockwave has passed, get into the nearest building as fast as you can.
- Use the time before fallout arrives. Ready.gov puts it at roughly 10 minutes or more. If a sturdy multi-story building, a basement, an underground parking garage or a subway is close enough to reach quickly, go there. If not, take the best shelter you can reach now rather than traveling in the open.
- Don’t try to drive away. A car is not a safe shelter in a radiation emergency. Leave decisions about evacuation to officials, who can tell you which direction is safe.
Where to shelter, wherever you are
The principle behind every row below is the one Ready.gov teaches: time, distance and shielding. Spend as little time exposed as possible, keep as far from the source as you can, and shield yourself inside a sturdy building. Brick or concrete buildings are better, and the most protected spot is deep inside, away from windows and outer walls.
| Where you are | Best option | Avoid |
|---|---|---|
| Home with a basement | Basement, in the part farthest from windows and outside walls | Rooms with windows; going outside to check |
| Home without a basement | The innermost room with no windows, with as many walls as possible between you and outside. If a sturdier multi-story or brick/concrete building is very close, consider moving there within the first minutes. | Spending time outdoors once fallout may be arriving |
| Apartment, office or other large building | Stay in the building and go to its center or basement, away from windows and outer walls; use an underground garage if there is one | Leaving the building to go home |
| Outdoors | Take cover and lie face down while the blast passes, then get into the nearest building | Staying outside to watch or film |
| In a car | Get into the nearest sturdy building | Sheltering in the car or joining traffic |
| Mobile home or light structure | These offer little shielding. Go to a sturdier building if you can reach one quickly; otherwise use the most interior space you have. | Traveling a long distance in the open |
If your family is split between home, work and school, each person should shelter where they are. Ready.gov advises learning your workplace and school sheltering plans in advance. Traveling to reunite during the first day means time outside, which is exactly what this guidance tells you to avoid.
The first 24 hours: stay inside and stay tuned
- Stay put for at least 24 hours. Ready.gov says to remain in the most protected location, such as a basement or the center of a large building, for the first 24 hours. Leave earlier only if told it is safe, or if an immediate danger like fire, a gas leak or collapse forces you out.
- Stop outside air coming in. Turn off fans, air conditioners and forced-air heating units that bring air in from outside. Close windows, doors and fireplace dampers.
- Keep pets inside. If people are told to stay inside, pets and service animals should be inside too.
- Listen for instructions. Ready.gov recommends a battery-powered or hand-crank radio, which keeps working if other communication fails. Follow official instructions on when and where to go. If you evacuate, don’t return until officials say it’s safe. Our hand-crank emergency radio guide compares models with NOAA weather band reception and backup power.
Cleaning off fallout (decontamination)
If you were outside after the detonation, start these steps once you’re inside and sheltered:
- Remove your outer layer of clothing. Ready.gov says this can remove up to 90% of radioactive material. Take it off carefully so you don’t shake dust loose, and avoid touching your eyes, nose and mouth. Put the clothing in the plastic bag from your kit and close it.
- Shower or wash with soap and water if you can.
- If you can’t shower, wash any skin and hair that wasn’t covered, or use a wipe or a clean wet cloth. Don’t use household cleaning wipes on skin. Hand sanitizer does not protect against radioactive material.
- Pets: gently brush their coat to remove particles, and wash them with soap and water if you can.
Food and water after a detonation
- Food and drinks that were inside a building are safe to eat and drink.
- Sealed containers that were outside are safe if you wipe them with a damp cloth before opening.
- Don’t eat garden produce or uncovered food or drinks that were outdoors until officials say it’s safe.
Plan to shelter with what is already inside. Our emergency water calculator and emergency food supply calculator size a household supply so you aren’t tempted to leave shelter early.
Potassium iodide (KI): what it does and doesn’t do
Potassium iodide is often sold as “anti-radiation pills.” The CDC’s KI guidance (reviewed January 2025) sets clear limits:
- KI protects only the thyroid, and only against radioactive iodine. It does not protect against other radioactive materials or the rest of the body.
- Don’t take KI unless public health or emergency officials, or a healthcare provider, tell you to.
- Don’t leave your shelter or home to look for KI. The CDC warns this could expose you to dangerous radiation.
- Use only FDA-approved KI products. Table salt and iodine-rich foods are not a substitute.
- Some people, including those with iodine sensitivity, shouldn’t take KI or should check with a healthcare provider first.
If you choose to keep KI at home, read the CDC page and follow official instructions in an emergency. The CDC’s main advice is still to get inside, stay inside and stay tuned.
Prepare now: alerts, kit and family plan
- Alerts: have more than one way to get emergency alerts. Ready.gov suggests the FEMA App and your local community alert sign-up.
- Radio: a battery-powered or hand-crank radio, with spare batteries if it uses them.
- Kit: sealed food, water and any essential medicine; a spare change of clothes for each person; and a heavy plastic trash bag for contaminated clothing. (Compare heavy-duty trash bags; we may earn a commission.)
- Family plan: choose a meeting place outside your home and an out-of-state contact. Learn the sheltering and evacuation plans at your school, workplace and any care facility. Our printable household emergency contact card keeps these details on paper for when phones are down.
- Know your shelter spots at home and at work in advance, so nobody has to think about it in the first minutes.
- Protect a few spare electronics if you want backups. Our guide to protecting electronics from an EMP explains what federal guidance recommends.
Print your nuclear emergency card
Why this page changed
Earlier versions of this page mixed blast trivia with advice that conflicted with current federal guidance. That included suggesting glow-in-the-dark plastics as radiation detectors and urging readers to head home or evacuate with a bug-out bag. We removed it. Official guidance is clear that sheltering in place comes first and that evacuation decisions belong to officials who know where fallout is going. For broader preparation, see our guide on how to prepare for war as a civilian.
How we researched this guide
Research method: This is a research-led summary of official guidance, not personal experience or expert certification. Every action step comes from Ready.gov’s Radiation Emergencies page (FEMA, updated January 7, 2025) or the CDC’s Potassium Iodide (KI) page (reviewed January 30, 2025). We checked both on November 7, 2026. We deliberately left out casualty estimates, fallout timing beyond Ready.gov’s statement, dose calculations and shelter construction. Follow local emergency officials if their instructions differ from this page.
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