Nuclear attack or war

The realistic picture

A nuclear explosion causes enormous damage within a few miles, but most of a region's population is outside that zone. For them, the avoidable risk is fallout: dust and particles that come down in the following hours. US emergency agencies sum up the response in three steps: get inside, stay inside, stay tuned.

Before: what you can prepare

• Identify the best shelter at home, work and school: a basement or the middle of a large concrete or brick building, away from the roof and outer walls. An underground garage or subway station also works.
• Keep water and food for at least two weeks, a battery radio, flashlights and your medication.
• Learn how alerts work in your country: sirens, phone alerts or radio.

During: the first minutes

1. Don't look at the flash. It can blind you temporarily even from far away.
2. If you're outside, lie face down behind something solid, cover your head and stay down until the blast wave passes, which can take tens of seconds to arrive. Then go into the nearest solid building.
3. Get inside and go down or to the center. The more mass (concrete, earth, brick) between you and the outside, the better. A car offers very little protection.
4. Stay at least 24 hours unless authorities say otherwise. Near the blast, fallout can start coming down within about 15 minutes.

If you were outside: decontaminate

• Take off your outer clothing as soon as you get in: it removes most of the contamination. Bag it and leave it away from people.
• Shower with warm water, soap and shampoo. Don't use conditioner: it binds particles to your hair.
• If there's no shower, wipe your skin with a damp cloth, blow your nose and wipe your eyelids, ears and eyelashes.
• Packaged food and bottled water are safe: wipe the outside of the container before opening it.

Potassium iodide: what it does and doesn't do

Potassium iodide tablets only protect the thyroid from radioactive iodine. They don't protect against other radiation and can have side effects. Take them only if public health authorities tell you to.

Afterwards

Come out only when authorities say so or if your shelter becomes unsafe (fire, collapse). Expect long power, water and communication outages: everything in the when help doesn't come guide applies. A large high-altitude detonation could also damage electronics, so a paper map and a spare radio are a good idea.