1. If there is a warning
Missile warnings, when they come at all, give minutes, not hours. Paris to New York is about twenty minutes of flight; between neighbouring countries it can be under ten. Do not spend that time trying to drive out of the city. Roads jam within minutes and a car offers no protection.
- Get inside the sturdiest building you can reach in a few minutes. Brick and concrete beat wood; a basement or the centre of a large building beats a top floor.
- Move away from windows. Flying glass is the most common injury far from ground zero.
- If you are caught outside with nothing nearby, lie flat in a ditch or behind a solid wall, face down, feet toward the likely blast, and cover your head.
2. The flash and the blast
The first sign of a detonation is a flash brighter than the Sun. Never look toward it: it can blind you even tens of kilometres away. The heat arrives with the flash and lasts a few seconds; anything you can put between you and the light, a wall, a car, a hill, cuts the burn.
The blast wave arrives after the flash, delayed by the speed of sound: about three seconds per kilometre. At 10 km from a large weapon you have roughly thirty seconds to drop to the ground and cover your head before the windows come in. Stay down until the wave has passed and the wind that follows it has dropped, then wait a moment: a second, weaker wave often follows.
3. The fallout window: get inside, stay inside
The most important thing you can do after a nuclear explosion is get indoors within about ten minutes and stay there. Fallout, the radioactive dust sucked up by the fireball, starts to come down downwind of ground zero within fifteen minutes and is most dangerous in the first hours.
- Go to a basement or the middle of a large building, as far from the roof and outer walls as possible. Every wall and floor between you and the outside cuts the dose.
- If you were outside when the fallout started, take off your outer clothes and seal them in a bag, wipe or wash exposed skin and hair, and blow your nose. Do not use conditioner; it binds particles to hair.
- Stay inside for at least 24 hours unless the authorities tell you to move. Radiation from fallout falls fast: the 7:10 rule says that for every sevenfold increase in time, the dose rate drops tenfold. Fallout that is lethal in the first hour is a hundred times weaker after two days.
- Keep pets inside with you.
Do not try to reach family members in the first hours. They are safest sheltering where they are, and you are safest where you are.
4. Information and health
- Keep a battery or hand-crank radio. Phone networks may be down or overloaded, and an electromagnetic pulse can damage electronics near the blast.
- Drink bottled or previously stored water. Tap water may be contaminated. Food in sealed containers or inside your home is safe to eat; wipe containers before opening.
- Potassium iodide tablets protect the thyroid against radioactive iodine only. They are useful after a reactor accident and much less so after a weapon; take them only if the authorities say so.
- Symptoms of radiation sickness, nausea and vomiting within hours, mean a serious dose. Rest, fluids and medical care as soon as it is safe to move.
5. What to have at home
The same kit that covers earthquakes, storms and blackouts covers a nuclear emergency: water for three days, food that needs no cooking, a first-aid kit, a radio, torches and batteries, medicines, copies of documents, and a plan for where the family shelters if separated. None of it is expensive, and having it means the first hour is spent sheltering rather than searching.