How to Prepare for a Nuclear Attack: A Practical Preparedness Guide

The Bulletin of the Atomic Scientists set the 2026 Doomsday Clock at 89 seconds to midnight, the closest it has ever been. The New START treaty between the US and Russia expired in February 2026 with no replacement. Iran's nuclear program continues to escalate, with the World Health Organization actively preparing for nuclear scenarios in the Middle East. None of this means a detonation is imminent. It means the window for preparation is open, and the people who use it will have better odds than those who do not.

This is a field guide for civilians. It covers what a nuclear detonation actually does, how to shelter effectively, what supplies to stage, and how to make decisions in the first minutes and hours after a blast.

Understanding the Threat: What Actually Happens

A nuclear detonation produces four effects that matter for survival planning: the blast wave, thermal radiation, initial nuclear radiation, and fallout.

For a 300-kiloton weapon (a common yield in modern arsenals), the Department of Health and Human Services Radiation Emergency Medical Management program maps the damage zones as follows:

• Severe damage zone: roughly 1.5 miles from ground zero. Structural collapse, lethal radiation doses above 500 rem, third-degree burns. Survival in this zone is unlikely without hardened shelter.
• Moderate damage zone: 1.5 to 3 miles. Buildings heavily damaged but partially standing. Injuries are severe but survivable with immediate shelter.
• Light damage zone: 3 to 9 miles. Broken windows, first-degree burns, flying debris. Most structures remain standing. This is where preparation makes the largest difference.

Fallout — radioactive particles carried by wind — can spread 50 to 200 miles downwind depending on conditions. According to FEMA's Nuclear Detonation Planning Guide, fallout is the largest geographic threat and the one most responsive to individual preparedness.

The 10-Minute Window

FEMA guidance states that after a nuclear detonation, you will have 10 minutes or more to find adequate shelter before fallout arrives. This is the single most actionable piece of information in nuclear preparedness.

What to do in that window:

1. Get inside the nearest solid structure. Brick, concrete, and earth are the best shielding materials. A basement is ideal. The center of a multi-story building works if no basement is available.
2. Move away from windows and exterior walls.
3. If you are in a vehicle, do not try to outrun the blast. Get to a building.
4. If you are outdoors and no building is available, find any terrain feature that puts mass between you and the blast — a ditch, a hill, a concrete wall.
5. Do not look at the fireball. A 1-megaton detonation can cause flash blindness up to 13 miles away on a clear day, according to nuclear effects data compiled by the Defense Nuclear Agency.

The instinct will be to run. Override it. Shelter-in-place is the correct response for the vast majority of people in the affected area.

Shelter Selection and Rating

Not all shelters are equal. The protection factor (PF) measures how much a structure reduces radiation exposure. A PF of 10 means you receive one-tenth the outside dose.

Shelter ratings by structure type:

• Underground parking garage or deep basement: PF 100-1000
• Multi-story concrete building (interior rooms, upper floors): PF 50-200
• Single-story brick or concrete building (center rooms): PF 10-50
• Wood-frame house (basement): PF 10-20
• Wood-frame house (no basement): PF 2-4
• Vehicle: PF 2-3

These numbers come from FEMA's Radiological Emergency Preparedness guidance. The takeaway: a concrete basement provides 50 to 100 times more protection than sitting in your car.

Shelter Scouting

Do this before any emergency. Walk your daily routes — home, work, school, commute. Identify the three best shelter options within a 5-minute walk of each location. Look for:

• Multi-story concrete or brick buildings
• Underground spaces (subway stations, parking garages, basements)
• Buildings with minimal windows on lower floors

Write these locations down. In a crisis, you will not have time to evaluate options.

Supplies: The 72-Hour Minimum

FEMA's nuclear detonation planning guidance indicates that people in most affected areas could leave shelter within a few days, though those in highest-radiation zones may need to shelter for up to a month. Plan for a minimum of 72 hours sealed inside a structure, with supplies to extend to 14 days if possible.

Water

Store 1 gallon per person per day. For a family of four sheltering 72 hours, that is 12 gallons minimum. For 14 days, 56 gallons. Use sealed containers only — any water exposed to fallout is contaminated until tested or filtered through appropriate radiological filtration.

Food

Sealed, shelf-stable food that requires no cooking. Canned goods, energy bars, freeze-dried meals, peanut butter. Avoid anything that requires opening windows or doors to ventilate cooking fumes. A manual can opener is a line item that gets overlooked constantly.

Medical

• A standard first aid kit
• A 14-day supply of any prescription medications
• Potassium iodide (KI) tablets, which protect the thyroid from radioactive iodine-131

Potassium Iodide: What It Does and Does Not Do

KI protects one organ (the thyroid) from one isotope (iodine-131). It does not protect against other forms of radiation. According to the CDC, taking KI within 1 to 2 hours of exposure blocks more than 90% of radioactive iodine uptake by the thyroid. After 4 hours, effectiveness drops sharply.

Dosage per CDC guidelines: 130 mg for adults, 65 mg for children 3-18, 32 mg for children 1 month to 3 years. Adults over 40 should only take KI when predicted exposure levels are high enough to risk hypothyroidism. Do not take KI unless directed by officials or a healthcare provider. Higher doses do not provide more protection and can cause severe illness.

Communications and Information

• Battery-powered or hand-crank AM/FM radio. NOAA Weather Radio frequencies (162.400-162.550 MHz) will carry emergency broadcasts.
• Spare batteries
• A whistle for signaling
• Paper copies of emergency contacts, rally points, and local shelter locations

If cell networks and the internet go down — which is likely in any nuclear event — your ability to access medical references, decontamination procedures, and fallout maps drops to whatever you have stored locally. The Deadnet USB drive carries 19 military and government survival documents, including Army field manuals covering nuclear defense and decontamination, along with a local AI assistant that runs without any internet connection. Having reference material that works offline is the point.

Decontamination

If you were outdoors when fallout arrived, or if you transited through a fallout zone to reach shelter, decontaminate before entering your shelter space.

FEMA's decontamination protocol:

1. Remove all outer clothing. This alone can eliminate up to 90% of radioactive contamination, according to Ready.gov guidance.
2. Place contaminated clothing in a plastic bag. Seal it and move it as far from occupied areas as possible.
3. Shower with soap and warm water. Scrub skin gently — do not abrade it. Radioactive particles on intact skin are far less dangerous than particles that enter through broken skin.
4. Shampoo hair but do not use conditioner. Conditioner binds radioactive particles to hair.
5. Blow your nose, wipe eyelids and eyelashes, and clean ear canals with a damp cloth.

If no shower is available, wipe exposed skin with clean wet cloths, working from the head down.

Evacuation vs. Shelter-in-Place

The default is shelter-in-place. Evacuation is appropriate only when:

• You are in the severe damage zone and your shelter is compromised
• Authorities issue specific evacuation orders with designated routes
• Radiation levels at your shelter remain dangerously high after 48-72 hours (requires a dosimeter to assess)

If you must evacuate, move crosswind — perpendicular to the wind direction — rather than downwind. Fallout plumes follow wind patterns. The FEMA nuclear detonation planning guide models fallout plumes as elongated ellipses extending downwind from ground zero, with the highest doses along the center line.

Equipment for Evacuation

• N95 or P100 respirator masks (to prevent inhaling radioactive particles)
• Sealed goggles
• Long sleeves, long pants, gloves, hat — any barrier between fallout particles and your skin
• Pre-planned route maps. Paper maps. GPS may not function.

Radiation Monitoring

A personal dosimeter or radiation survey meter gives you data to make decisions. Without one, you are guessing.

The Nuclear Regulatory Commission recommends that people limit their total exposure to no more than 1 rem (10 mSv) above normal background radiation per year under non-emergency conditions. In an emergency, dose limits are higher — FEMA planning guidance allows up to 5 rem for lifesaving activities.

Affordable options include:

• RADTriage personal dosimeters (card-format, about $25, single-use)
• NukAlert keychain detector (around $160, reusable, chirps to indicate radiation levels)
• Survey meters from civil defense surplus (variable quality, verify calibration)

Family Communication Plan

Assume phones will not work. Establish in advance:

• A primary rally point within walking distance of home
• A secondary rally point outside your immediate area (a relative's house, a public landmark)
• An out-of-state contact person. After regional disasters, long-distance calls often work when local circuits are overloaded. FEMA recommends designating one out-of-area contact that all family members know to call.
• Written cards for each family member with contact numbers, rally points, and blood types

Rehearse this plan. A plan that exists only on paper is better than nothing, but a plan that has been practiced is the one people actually follow under stress.

Long-Term Considerations

Radioactive fallout decays rapidly. The 7-10 rule is the standard estimation tool: for every 7-fold increase in time after detonation, radiation intensity decreases by a factor of 10. At 49 hours (7 x 7), radiation is 1% of its 1-hour level. This means the first 24-48 hours are the most dangerous, and conditions improve significantly each day.

Long-term concerns include contaminated water supplies, disrupted food distribution, and medical system overload. FEMA's 2026 operational status already faces strain — the Disaster Relief Fund has been depleted during an ongoing DHS shutdown, limiting the agency's capacity even before a nuclear event.

This is where self-sufficiency becomes the practical reality. Having offline access to water purification procedures, wound care protocols, and food safety guidelines means you are not dependent on infrastructure that may not exist for weeks or months. The Deadnet USB includes field manuals covering water treatment, emergency medicine, and long-term survival operations — all readable on any laptop without power grid or internet access.

Your Next Step

Today, not tomorrow: walk your daily route and identify three shelter locations within 5 minutes of where you spend most of your time. Write them down on a card. Put that card in your wallet. This takes 30 minutes and costs nothing, and it directly addresses the most time-sensitive decision you will face in a nuclear emergency — where to go in the first 10 minutes.