Nuclear Preparedness Guide: What to Do Before, During, and After a Nuclear Event

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 expired on February 5, 2026, ending decades of legally binding limits on the world's two largest nuclear arsenals. The WHO is actively updating protocols for nuclear scenarios in the Middle East. The Arms Control Association reports growing proliferation risks from Iran, South Korea, and Saudi Arabia.

None of this means a nuclear event is imminent. All of it means your window to prepare is now, not after a flash on the horizon.

This guide covers what you can actually do: the supplies, the shelter math, the medical basics, and the 72-hour survival plan that FEMA's own nuclear detonation response guidance is built around.

Understanding the Threat Spectrum

Not all nuclear events are the same, and your response depends on what you are facing.

A nuclear detonation produces three immediate threats: blast wave, thermal radiation, and ionizing radiation. The blast wave from a 10-kiloton device (the size intelligence agencies consider most likely for a terrorist weapon) causes severe structural damage within a 0.5-mile radius, according to FEMA's Nuclear Detonation Planning Guide. A state-level weapon in the hundreds of kilotons extends that radius significantly.

A reactor accident or dirty bomb produces no blast wave but distributes radioactive material over a wide area. The Chernobyl exclusion zone still covers 2,600 square kilometers nearly 40 years later.

The common thread across all these scenarios: your survival depends on shielding, distance, and time. The more mass between you and the radiation source, the farther you are from ground zero, and the longer you wait for short-lived isotopes to decay, the better your odds.

Shelter: The Math That Saves Your Life

FEMA TR-87 sets the minimum protection factor (PF) for public fallout shelters at PF 40, meaning the shelter reduces your radiation exposure to 1/40th of the outside level. But you do not need a purpose-built bunker to hit that number.

The protection factor of common structures, based on Department of Energy and NIST studies:

• A wood-frame house with no basement: PF 2 to 3
• A wood-frame house with a basement: PF 10 to 20
• A concrete or brick building, ground floor: PF 10 to 20
• A concrete basement: PF 40 to 100
• The center of a large concrete or brick building, middle floors: PF 100 or higher
• A dedicated underground shelter with 24 inches of concrete: PF 1,000

The US Army field manual FM 3-4 confirms that a standard basement reduces radiation exposure by a factor of 10 compared to aboveground floors. The EPA's RadTown data shows that concrete walls act as a measurable barrier between you and external gamma radiation, with every 2.4 inches (6 cm) of concrete cutting gamma ray intensity by half.

Your action item: identify the best shelter location within 10 minutes of every place you spend significant time. Work, home, daily commute. The shelter does not need to be perfect. A PF 10 building keeps you alive long enough for the most dangerous short-lived isotopes to decay.

The 7-10 Rule of Fallout Decay

Radioactive fallout follows a predictable decay curve. For every sevenfold increase in time after detonation, radiation intensity drops by a factor of 10.

• 1 hour after detonation: baseline radiation level (call it 1,000 units)
• 7 hours: 100 units (10% of initial)
• 49 hours (roughly 2 days): 10 units (1% of initial)
• 14 days: 1 unit (0.1% of initial)

This is why FEMA's 72-hour nuclear detonation response guidance treats the first 24 hours as the most dangerous period and why their default instruction is shelter-in-place for a minimum of 24 hours, possibly longer depending on fallout patterns. After 48 hours, radiation levels have typically dropped enough that brief outdoor exposure for relocation becomes survivable.

You need to be able to survive indoors for at least 72 hours without outside help. That is the baseline your supply planning should target.

The Nuclear Emergency Kit

Your nuclear kit is not a separate bag. It is a set of additions to a standard 72-hour emergency kit, focused on the specific threats of radiation.

Shelter-in-place supplies (per person, 72-hour minimum):

• Water: 1 gallon per person per day, minimum 3 gallons stored. CDC guidance confirms this as the standard for emergency water planning.
• Food: 3 days of non-perishable food requiring no cooking. Canned goods, energy bars, peanut butter.
• Plastic sheeting and duct tape: for sealing windows and doors against fallout particles entering your shelter space. Pre-cut sheets to fit your designated shelter room.
• N95 or P100 respirator masks: standard N95 masks filter particles 0.3 microns and larger at 95% efficiency, which covers most fallout particulate matter.
• Potassium iodide (KI): available over the counter at pharmacies without a prescription. The CDC recommends 130 mg for adults, 65 mg for children ages 3-18. One dose protects the thyroid for 24 hours. Taken within 1-2 hours of radioactive iodine exposure, KI blocks over 90% of thyroid uptake. After 4 hours, effectiveness drops sharply. The FDA recommends KI primarily for people under 40 and pregnant or breastfeeding women.
• Battery-powered or hand-crank NOAA weather radio: your primary information source when cell networks and internet are down. NOAA radio covers 95% of the US population according to the National Weather Service.
• Flashlights and extra batteries, or a hand-crank flashlight
• First aid kit with a 14-day supply of prescription medications
• Garbage bags and ties for sanitation
• Wrench or pliers for turning off utilities
• Dosimeter or radiation detector card (optional but valuable for making informed decisions about when to move)

The Deadnet USB includes the full FEMA Nuclear Detonation Response Guidance and FM 3-4 Nuclear Protection field manual among its 19 military and government source documents. These references are readable offline through the onboard AI assistant, which matters when your phone is a brick and the internet is down.

Decontamination Protocol

If you were outdoors during fallout, the Red Cross decontamination procedure is straightforward:

1. Remove all outer clothing. This single step can eliminate up to 90% of radioactive contamination on your body, according to CDC radiation emergency guidance.
2. Place contaminated clothing in a plastic bag. Seal it and move it as far from living spaces as possible.
3. Shower with soap and warm water. Scrub gently. Do not use conditioner, as it binds radioactive particles to hair.
4. Blow your nose, wipe your eyelids and ears with a clean wet cloth.
5. If no shower is available, wipe all exposed skin with clean wet cloths or uncontaminated wipes.

Do not scrub skin raw. Do not use bleach or harsh chemicals. Intact skin is already a barrier against alpha and beta radiation. Your goal is removing particles, not sterilizing.

Communication and Information

After a nuclear event, standard communication infrastructure will be degraded or destroyed within the blast zone, and overloaded everywhere else. FEMA's post-detonation communication guidance acknowledges that cellular networks will likely be non-functional for an extended period.

Your communication plan should include:

• A designated out-of-area contact person that all family members know to reach
• A physical meeting location if communication fails entirely
• A battery-powered AM/FM/NOAA radio for receiving emergency broadcasts
• Written copies of emergency phone numbers (not just stored in your phone)
• A hand-crank or solar USB charger for devices

The bigger information problem is access to reference material. Medical procedures for radiation exposure, water purification methods, fallout decay calculations, shelter improvement techniques — this is information you need after the event, when you cannot look it up online.

Deadnet was built for this scenario. The offline AI and its library of military field manuals, FEMA guides, and survival references sit on a USB drive that works on any laptop, no internet required. When the grid is down and cell towers are out, having 19 source documents and an AI that can search and explain them is a practical tool, not a luxury.

Evacuation vs. Shelter-in-Place

The default action for a nuclear event is shelter-in-place. FEMA's guidance is clear: stay inside for at least the first 24 hours unless your building is structurally damaged or on fire.

However, evacuation may be necessary if:

• Your shelter provides a protection factor below PF 5 (a mobile home or vehicle)
• You are downwind of the detonation and can reach a PF 40 or better shelter within 15 minutes
• Authorities issue evacuation orders after initial fallout has subsided

If you evacuate, move perpendicular to the wind direction, not directly away from the blast. Fallout travels with the wind in an elongated plume pattern. Moving sideways gets you out of the plume faster than moving along its length.

Keep vehicle windows closed and ventilation set to recirculate. Do not use the intake fan setting, which pulls outside air (and fallout particles) into the cabin.

Long-Term Considerations

If you survive the first 72 hours, your priorities shift to:

Water sourcing: Groundwater and sealed water supplies are generally safe. Open water sources exposed to fallout need testing or treatment. Fallout particles settle, so water drawn from below the surface of a contaminated source is safer than surface water. FEMA recommends letting particulate settle and drawing from the middle of the water column if no clean source is available.

Food safety: Canned and sealed foods are safe regardless of external contamination. Wash the exterior of cans before opening. Fresh food that was exposed to fallout should be peeled or the outer layers discarded. Root vegetables that were underground during fallout are safer than leafy greens.

Medical triage: Acute Radiation Syndrome (ARS) symptoms appearing within the first hour — nausea, vomiting, diarrhea — indicate a high dose exposure. The CDC notes that onset of vomiting within 1 hour suggests an exposure above 4 Gy, which requires immediate medical attention if available. Symptom onset after 6 hours suggests a lower, more survivable dose.

Community coordination: Within 48-72 hours, mutual aid networks will matter more than individual supply caches. Know your neighbors. Identify who has medical training, mechanical skills, communications equipment, or additional shelter capacity.

Preparing Children and Vulnerable Populations

The CDC's KI dosage recommendations scale by age: 65 mg for children 3-18, 32 mg for children 1 month to 3 years, and 16 mg for newborns. Stock the appropriate dosage.

Children under 40 lbs need approximately half a gallon of water per day rather than a full gallon. Elderly individuals and those on medications may need more.

Have comfort items available for children — books, small games, familiar objects. A 24-72 hour shelter-in-place with children in a sealed room will be psychologically difficult. Preparing them with age-appropriate information beforehand reduces panic.

For individuals with mobility impairments, identify a ground-floor or basement shelter space that is accessible. Pre-position supplies there rather than counting on rapid movement during an emergency.

Your Next Step

Do one thing today: walk through your home and workplace and identify the highest-PF shelter location in each. The interior of a basement, the center of a concrete building, a below-grade parking structure. Time the walk from your desk, your bed, your car to that location. Write down the time. If it is over 10 minutes, find a closer option. That single piece of knowledge — knowing exactly where to go and how fast you can get there — is the foundation everything else builds on.