SURVIVAL GUIDE · BASED ON OFFICIAL GUIDANCE

What to Do in a Nuclear Attack: The First Minutes and the Next 48 Hours

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Most people outside the immediate blast area of a nuclear explosion can survive if they know what to do. The official advice from FEMA fits in six words: Get inside. Stay inside. Stay tuned. This guide explains each step in the order you would face it, with the reasons and sources behind it.

1. When the alert sounds

An air-raid alert means you may have only minutes. Move first and check the news later. Go to the nearest underground space: a deep subway station, an underground parking garage or the basement of a large building. In South Korea, designated civil defense shelters can be found in the government's Emergency Ready app (안전디딤돌).

• Use the stairs, not the elevator. Elevators can stop during an alert, a power cut or the blast and trap you.
• Don't try to drive away. Roads jam within minutes, and a car gives almost no protection from radiation.
• Text instead of calling. Voice networks overload in a disaster, but short text messages usually still get through.
• If it takes only seconds, grab water, a flashlight and a portable radio on your way.

2. If you see the flash

The light of a nuclear explosion arrives instantly. Looking at it can cause flash blindness for several minutes, and closer in, burns to the retina. Close your eyes, turn away and drop face down, ideally behind something solid and away from windows. Cover your head with your arms and keep your mouth slightly open to reduce pressure injuries.

The blast wave travels at the speed of sound, about 340 meters per second, so it arrives seconds after the flash. Stay down until it has passed. Broken glass is one of the main causes of injury: when a meteor exploded over Chelyabinsk, Russia, in 2013, most of the roughly 1,500 people hurt were injured by flying glass.

3. Before the fallout arrives

Fallout is radioactive dust carried up by the explosion that falls back to the ground over the next minutes to hours, drifting downwind. Depending on distance and wind, it can start falling within roughly 10 minutes to an hour. Use that time to get to the best shelter you can reach.

• Go deep and go to the middle. Thick soil and concrete block radiation. The center of a deep basement in a large building can cut outdoor radiation to 1/100 or less.
• Stay away from entrances and outer walls. Radiation comes in through openings.
• Avoid the worst places: cars, rooftops, the top floors of buildings, and elevated stations or spaces under overpasses that are open to the sky.
• Fallout goes underground, chemical gas goes up. For a chemical attack the advice is the opposite: go to a high floor. Confirm through official alerts which one it is.

4. The next 48 hours in the shelter

Fallout radiation weakens quickly. Under the 7-10 rule, it drops to about 1/10 after 7 hours, about 1/100 after two days and about 1/1000 after two weeks. That is why the first day or two underground matters most.

• Stay at least 24 hours, and longer if officials tell you to. Going outside after only a few hours is one of the biggest causes of exposure.
• Seal gaps and turn off ventilation to keep radioactive dust out.
• Remove your outer clothing if you were outside. Bag it and keep it away from people. This alone removes about 90% of radioactive material.
• Wash with soap and shampoo, but not conditioner, which binds radioactive material to hair. If you can't shower, wipe exposed skin with a damp cloth.
• Drink stored tap water or bottled water. Don't drink rainwater after the blast: it can carry fallout. Sealed and packaged food is safe.
• Never run a car engine in a closed garage. Carbon monoxide builds up quickly.
• Use a plastic bag as a toilet instead of going outside, even for a few minutes.
• Save your phone battery and use it for text messages and official alerts.

5. Potassium iodide, rumors and family

Potassium iodide (KI) protects only the thyroid and has side effects. Take it only when health officials tell you to. It does not protect you from fallout in general.

Trust official broadcasts only. In a disaster, rumors in group chats spread faster than facts, and following them can lead people out into the fallout. A portable radio works even when the power and mobile networks are down.

Don't go looking for your family. It is the hardest rule to follow, but walking outside during the first hours of fallout is the most dangerous thing you can do. Everyone should shelter where they are and keep in touch by text.

6. When it is time to leave

Move only when officials announce it, usually after 24 to 48 hours. Cover your nose and mouth with a mask, wear long sleeves and a hat, and travel across or against the wind, never in the direction the wind is blowing. Bring your ID: you will need it to register at relief centers and to get medical help.

Emergency kit checklist

• Water (several liters per person)
• Portable radio and spare batteries
• Flashlight or headlamp
• Power bank
• Masks and gloves
• Plastic bags (clothing, toilet)
• First aid kit and your medicines
• Long-lasting food
• ID card
• Warm clothes or a blanket

Practice it in a simulation

Reading a list is easy. Remembering it while your phone is screaming is not. Nuclear Blast: 20 Minutes to Fallout is a free browser game that puts you on the 18th floor of a Seoul office three minutes before a blast and lets you make every one of these decisions under time pressure. See the game guide.

Sources

• FEMA, Planning Guidance for Response to a Nuclear Detonation (2022)
• Ready.gov, “Nuclear Explosion” (Get inside, stay inside, stay tuned)
• US CDC, Radiation Emergencies: decontamination and sheltering
• Ministry of the Interior and Safety (Korea), National Disaster Safety Portal and civil defense guidance
• Nuclear Safety and Security Commission (Korea) and WHO: potassium iodide
• Glasstone & Dolan, The Effects of Nuclear Weapons (1977)

This page is general information for education, not official emergency guidance. In a real emergency, follow the instructions of your local authorities.

FAQ

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