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

In March 2026, the Office of the Director of National Intelligence published its Annual Threat Assessment, identifying nuclear proliferation as a growing concern across multiple theaters. The Bulletin of the Atomic Scientists maintains the Doomsday Clock at its closest-ever position to midnight, citing ongoing nuclear risk between major powers. The World Health Organization is actively preparing for nuclear-related scenarios in the Middle East. New START — the last arms control agreement between the US and Russia — expired in February 2026 with no replacement.

This is not alarmism. This is the operating environment. What follows is a practical guide to nuclear preparedness based on federal planning documents, physics, and field-tested principles.

Understanding the Threat: What Actually Happens

A nuclear detonation produces three immediate effects: blast wave, thermal radiation, and ionizing radiation. A fourth — radioactive fallout — follows within minutes to hours depending on wind and yield.

According to FEMA's Nuclear Detonation Response Guidance, the most survivable scenario for most people is not the blast itself but the fallout period that follows. The agency's planning documents state that adequate shelter and a 72-hour action plan can save tens of thousands of lives in a single event.

The key number: you have approximately 10 minutes after a detonation to find adequate shelter before fallout begins arriving at ground level. That window is your margin. Everything in this guide works backward from it.

Shelter: Your Single Highest-Priority Prep

Shelter is not optional. It is the primary survival variable in a nuclear event. FEMA assigns a Protection Factor (PF) rating to different structures — this measures how much a shelter reduces your radiation exposure compared to standing in an open field.

Here is what the data shows:

• A wood-frame house provides a PF of roughly 2.5, reducing radiation by about 60%
• A brick house provides a PF of roughly 5, reducing exposure by 80%
• A basement in a concrete or brick building can reach PF 10-40, cutting exposure by 90-97.5%
• The center of a multi-story concrete building can exceed PF 200
• A purpose-built fallout shelter can reach PF 1,000 or higher

FEMA considers PF 40 the standard for public fallout shelters. At PF 40, only 2.5% of outside radiation reaches you. For context, a concrete basement with 12 inches of overhead concrete and earth cover meets this threshold.

Identifying Shelter Now, Not Later

Walk your daily routes — home, work, school. Identify the best shelter option within a 5-minute sprint of each location. You are looking for:

• Basements of commercial or government buildings
• Interior rooms of multi-story concrete or brick structures
• Underground parking garages
• Subway stations

If you live in a wood-frame house with no basement, identify the nearest concrete structure. Know how to get there in under 5 minutes on foot. After a detonation, roads will be impassable.

Improvised Shelter Hardening

If you cannot reach a purpose-built shelter, you can increase the PF of any room by adding mass between you and the outside. Every 3.6 inches of concrete or 7.2 inches of packed earth halves the radiation dose passing through it. Stack books, furniture, bags of soil, or water containers against exterior walls and above your position. A water heater in a closet against an interior wall is better than a living room with floor-to-ceiling windows.

The 72-Hour Supply Kit

FEMA's nuclear detonation planning guidance centers on a 72-hour window — the period during which fallout radiation decays most rapidly and shelter discipline is most important. After 72 hours, radiation drops to roughly 1% of its 1-hour level through natural decay (the "7-10 rule": for every 7-fold increase in time after detonation, radiation drops by a factor of 10).

Your kit should sustain shelter-in-place for at least 72 hours and ideally 14 days. FEMA's own planning documents recommend preparing for up to two weeks of sheltering.

Water

• 1 gallon per person per day, minimum. The CDC baseline is 3 days; for nuclear preparedness, stock 14 days if possible.
• Store in sealed, food-grade containers away from direct sunlight.
• Water purification tablets or a gravity filter rated for 0.2 microns as backup. Note: standard water filters do not remove radioactive particles. If your water source may be contaminated with fallout, let it settle for 48 hours, decant the top, then filter.

Food

• Canned goods, freeze-dried meals, energy bars — anything that requires no refrigeration and minimal water to prepare.
• 2,000 calories per person per day minimum.
• Manual can opener. This is the single most-forgotten item in emergency kits.
• If you have infants, stock ready-to-feed formula (not powder, which requires clean water).

Medical and Protective

• N95 masks or higher — rated to filter particles down to 0.3 microns, which captures most fallout particulate
• Plastic sheeting and duct tape for sealing windows and doors
• A basic trauma kit: gauze, tourniquets, chest seals, hemostatic agents
• Potassium iodide (KI) tablets

Communications and Information

• A battery-powered or hand-crank AM/FM/NOAA weather radio. This is your primary information source when cell networks are down.
• Spare batteries in a sealed bag.
• A printed list of emergency frequencies for your area.

This is where an offline reference source becomes directly relevant. The Deadnet USB drive includes FEMA's nuclear detonation response guidance, military field manuals covering radiological defense, and a local AI assistant that can answer follow-up questions — all without requiring internet or cell service. When communication infrastructure fails, having reference material physically in hand changes your decision quality.

Potassium Iodide: What It Does and Does Not Do

KI is one of the most misunderstood preps in nuclear preparedness. Here is what the CDC and FDA actually say.

Potassium iodide saturates your thyroid gland with stable (non-radioactive) iodine, preventing it from absorbing radioactive iodine-131 released during a nuclear event. One dose provides protection for approximately 24 hours.

Who Should Take It

The FDA prioritizes KI for people under 40, with infants, children, and pregnant or breastfeeding women at highest priority. Adults over 40 have the lowest risk of radioiodine-induced thyroid cancer and are least likely to benefit.

What KI Does Not Do

• It does not protect against any radiation other than radioactive iodine
• It does not protect any organ other than the thyroid
• It is not a general anti-radiation drug
• Taking more than the recommended dose does not increase protection and can cause severe illness

Dosing

According to FDA guidelines: adults and adolescents over 68 kg get 130 mg. Children 3-18 get 65 mg. Children 1 month to 3 years get 32 mg. Newborns get 16 mg. Do not take KI unless directed by public health officials or a healthcare provider.

Stock KI if you choose, but understand it is one narrow tool — not a substitute for shelter discipline.

Fallout: The Physics You Need to Know

Fallout is pulverized debris — soil, building materials, weapon components — that has been irradiated and lofted into the atmosphere. It falls back to earth as radioactive dust and ash, contaminating surfaces and water sources.

The 7-10 Rule

For every 7-fold increase in time after detonation, radiation intensity drops by a factor of 10. Practically:

• 1 hour after detonation: full intensity
• 7 hours: 10% of initial intensity
• 49 hours (~2 days): 1% of initial intensity
• 343 hours (~2 weeks): 0.1% of initial intensity

This is why the first 24-48 hours of shelter discipline are so high-value. The radiation is decaying rapidly, but those first hours are when exposure is most dangerous.

Decontamination

If you were outdoors when fallout arrived:

1. Remove all outer clothing before entering shelter. This alone removes up to 90% of contamination, according to Ready.gov guidance.
2. Bag the clothing and leave it outside your shelter area.
3. Shower or wash with soap and water. Do not use conditioner — it binds radioactive particles to hair.
4. Blow your nose, wipe eyelids and ears with a damp cloth.
5. Put on clean clothing from inside the shelter.

Planning for a Family

If you have dependents — children, elderly family members, people with disabilities — your plan needs additional layers.

Reunification

Establish a pre-agreed shelter location. If the event happens during work/school hours, each family member should know: go to the nearest adequate shelter, stay there for a minimum of 24 hours, then attempt reunification only when radiation levels are confirmed to be dropping. FEMA's guidance is explicit: do not go outside to search for family members during the first 24 hours. The instinct to do so is the single highest cause of preventable deaths in fallout scenarios.

Children at School

Contact your child's school and ask about their shelter-in-place plan for radiological events. Many schools have no plan. If yours does not, advocate for one. At minimum, know which room in the school building has the highest protection factor — typically an interior room on the lowest floor.

Medications

Stock a 30-day supply of all prescription medications. In a nuclear event, pharmacies will be inaccessible for weeks. If you depend on refrigerated medication (insulin, certain biologics), have a plan for battery-powered cooling.

Digital Preparedness: Reference When Infrastructure Fails

After a nuclear event, expect total failure of: cellular networks, internet service, GPS, and broadcast television. AM/FM radio and NOAA weather radio will likely be the only functioning broadcast systems, and even these may have gaps in coverage.

This is the gap that offline reference material fills. Having FEMA's full nuclear detonation response guidance, military NBC (Nuclear, Biological, Chemical) defense manuals, and medical references stored locally — on a device like the Deadnet USB — means you can look up decontamination procedures, fallout decay calculations, or medical triage protocols without any network connection. The difference between having a reference and guessing from memory is the difference between effective shelter management and avoidable mistakes.

What to Store Digitally

At minimum, keep offline copies of:

• FEMA's "Nuclear Detonation Response Guidance: Planning for the First 72 Hours" (publicly available PDF)
• Ready.gov's radiation emergency action guides
• A basic medical reference covering radiation sickness symptoms and treatment
• Local maps with shelter locations marked
• Emergency contact information and your family reunification plan

Store these on a USB drive kept in a Faraday-type protective bag to shield against electromagnetic pulse effects.

The Training Gap

Having supplies and a plan is necessary but not sufficient. FEMA's own after-action reports consistently identify the same failure: people who had plans but never practiced them made the same mistakes as people with no plan at all.

Practice the following quarterly:

1. Shelter sprint: from your current location, get to your identified shelter within 5 minutes. Time it.
2. Kit check: verify all water, food, batteries, and medications are within date. Rotate stock.
3. Family drill: run through the reunification protocol with all family members. Make sure children can state the shelter location and the 24-hour rule from memory.
4. Radio check: turn on your emergency radio, verify it works, confirm you can find your local NOAA frequency.

What to Do Right Now

Do not wait for a crisis to begin preparing. The single most effective action you can take today: identify the highest-PF shelter within a 5-minute walk of your home and workplace. Walk the route. Time it. Tell your family.

Then build your 72-hour kit. Water first — 1 gallon per person per day, 3 days minimum. That is your foundation. Everything else builds on top of those two actions: a known shelter and water to sustain shelter-in-place.

The threat environment in 2026 is not theoretical. The DNI's own assessment, the WHO's preparations, and the collapse of bilateral arms control all point in the same direction. Preparedness is not paranoia. It is a rational response to stated conditions.