15.4 If you see the flash

There may be no warning. If there is an alert of an imminent attack, go immediately into the nearest building and move away from windows. If the flash catches you by surprise:

1. Do not look. Do not turn toward the light or go to the window to see what happened. Curiosity causes blindness and glass injuries.
2. Get down, face down. Behind something solid if there is anything: a wall, a high curb, a parked car, a ditch. Lying face down protects exposed skin from the heat and debris (FEMA). Cover your head and the back of your neck with your arms; tuck your hands under your body.
3. If you are indoors: move away from windows and glass doors. Drop to the floor next to an interior wall or under a sturdy piece of furniture.
4. Wait for the blast wave. The sound and wind arrive after the light. Several miles away, the wave travels about 1 mile every 5 seconds: at 3 miles (5 km) it takes about 15 seconds; at 10 miles (16 km), almost a minute. Do not get up as soon as the light passes.
5. Stay down until the wind passes and debris stops falling. The Health Physics Society recommends staying under cover for at least 2 minutes after the flash.
6. Get inside. As soon as the wave passes, go to the best building you can reach in a few minutes. You have 10 minutes or more before the fallout arrives; in areas outside the damage area, often more than 15 minutes, and in many areas an hour or more (FEMA).

The first 10–15 minutes: where to go

Ready.gov says: go to a basement or a sturdy multistory building if you can reach it in minutes. If not, go into the nearest building. The practical rule:

• If you are inside a good building (concrete or brick, multiple floors, with a basement or interior core): stay and go to the center or the basement.
• If you are in a light building and there is a much better one 2–5 minutes away on foot or running: go, and arrive before 10 minutes have passed since the explosion.
• If you are not sure, if there are injured people or debris in the way, or if a lot of time has already passed: go into the nearest building and stay.
• If you are in a car: park in a safe place and go into a building. An underground parking garage or the center of an office building is much better than the car.

If you must be outside even for a moment, cover your nose and mouth with a face mask, cloth, or towel (CDC). Before going in, if you can, take off your outer layer of clothing.