The short answer: get inside the nearest sturdy building, go to the basement or the middle of it, and stay at least 24 hours unless officials say otherwise. Listen for instructions on a battery radio. Official agencies call this get in, stay in, tune in.
Almost nobody wants to read about this. If it ever happened, everything in you would want to run to the car or go and find your children. That instinct comes from love. It’s also what official guidance warns against most.
Nothing here predicts anything. It’s like knowing where the fire exit is. FEMA says most lives can be saved in the first 60 minutes, and that simply sheltering could save hundreds of thousands of people in a major city.
If you see a sudden, intense flash
You may have only seconds before the blast arrives, so act before you think.
- Get away from windows. Flying glass causes many of the injuries.
- Close your eyes. Don’t look at the flash.
- Lie flat, face down, until the heat and shock waves have passed.
- Then get inside straight away. Ready.gov says you’ll have 10 minutes or more before fallout arrives.
Where to hide
Fallout is radioactive dust that settles on roofs and on the ground. So you want as much heavy material as possible between you and the outside, and as much distance from the roof and outer walls.
- Best: underground spaces, such as parking garages and subways, or the center of a large concrete or brick building.
- Good: a house with a basement, or the middle of a multi-story building.
- Limited: the center of a light single-story house.
- Very poor: a car. CDC says cars do not provide good protection.
Most homes in the world have no basement. That’s fine. Use the room or hallway furthest from the roof and outer walls, or a shared stairwell in a large block. Any building beats being outside.
How long to stay inside
Plan for at least 24 hours. Fallout fades fast at first, and scientists use a rule of thumb: every time the hours since the blast multiply by seven, radiation falls about ten times. So at 7 hours, it’s about 10% of the level at 1 hour. At 2 days, it’s about 1%.
Leave only for fire, collapse, a gas leak or a life-threatening emergency. If there’s no news after 24 hours, guidance says staying longer may be better if you have food, water and medicine.
The hardest part: don’t go out for your family. CDC warns that going out could expose you and them to dangerous radiation. Text instead of calling, and agree this rule together now, while everyone is calm.
What to do once you’re inside
- Close up. Shut windows and doors, and turn off fans and air conditioning that bring in outside air.
- Take off your outer clothes carefully and seal them in a bag. This can remove up to 90% of radioactive material.
- Wash with soap and shampoo. No conditioner, because it makes radioactive material stick to your hair.
- Turn on a battery or hand-crank radio. Instructions will change as officials learn where fallout has gone.
What to eat and drink
The rule is simple. Food that was indoors or in a sealed container is safe. Wipe cans and packets with a damp cloth before you open them. Don’t eat open food from outside, or anything from your garden, until officials say so.
For drinks, start with bottled water and sealed drinks. Tap water is for when nothing else is available, and boiling doesn’t remove radioactive material. It’s still fine for washing.
Phones may not work when you need this
Have the plan on paper
The Nuclear Emergency Plan is 32 printable pages built from official guidance: a one-page card for the fridge, first aid, babies and medicines, and a family plan you fill in once.
Instant PDF download. Not for you? Email us within 14 days for a full refund. See our refund terms.
Quick questions
Is a car safe in a nuclear explosion?
No. Find a building right away and go in. Roads may also be blocked.
Should I take potassium iodide?
Only if health authorities tell you to. WHO says it isn’t an antidote to radiation. It protects only the thyroid, from one type of radioactive material, and iodized salt can’t replace it.
Is it safe to shower afterwards?
Yes. Tap water can be used for washing, even if officials say not to drink it.
Is this the same as a nuclear power plant accident?
No, it’s a different event. Ready.gov says the basic steps are the same in any radiation emergency, but always follow your local authorities.
Sources: FEMA, Ready.gov, CDC and WHO. Much of this guidance was written in the United States, so instructions from your own national and local authorities always come first. This is general safety information, not medical advice, and no guide can promise anyone’s safety.
Looking for something lighter? Read what happens to your body when you eat a banana every day.