Nuclear Preparedness Guide: What You Actually Need to Know and Do

In January 2026, the Bulletin of the Atomic Scientists moved the Doomsday Clock to 85 seconds to midnight — the closest it has ever been since the Clock was created in 1947. The factors cited: expanding nuclear arsenals, the expiration of New START (the last US-Russia arms control treaty) in February 2026, and growing proliferation risks from Iran and other states. The 2026 Annual Threat Assessment from the Director of National Intelligence estimates that the collective missile threat to the US homeland will expand from over 3,000 missiles today to more than 16,000 by 2035.

None of this means a nuclear detonation is likely tomorrow. It means the probability is nonzero and rising, and the window to prepare is before an event, not during one. This guide covers what actually happens in a nuclear detonation, what the science says about survival, and exactly what you need on hand.

The 10-Minute Window

After a nuclear detonation, you have roughly 10 to 15 minutes before radioactive fallout begins arriving at locations downwind of the blast. This number comes directly from FEMA's Nuclear Detonation Response Guidance, developed in coordination with Lawrence Livermore National Laboratory.

What you do in those 10 minutes determines your radiation exposure for the next 48 hours. The priorities, in order:

1. Get inside the nearest solid structure. A concrete or brick building with a basement is the target. Do not attempt to drive away — traffic will gridlock within minutes, and you will be caught in the open when fallout arrives.
2. Move to the interior. Put as many walls and as much mass between you and the outside as possible. A basement is the single best option in a residential setting.
3. Seal the space. Close all windows and doors. Turn off HVAC systems, fans, and anything that pulls outside air in.
4. Stay put. Do not leave for at least 24 hours unless directed by emergency authorities via radio.

At a distance of 20 to 25 miles downwind from a detonation, a person who does not find shelter within 25 minutes of fallout arrival will accumulate a lethal radiation dose of 600 rads, according to data from the Department of Defense's nuclear weapons effects research.

How Fallout Decays: The 7-10 Rule

Fallout radiation follows a predictable decay curve. The rule is simple: for every 7-fold increase in time after detonation, radiation drops by a factor of 10.

• At 7 hours: radiation is 1/10th of the initial level
• At 49 hours (7 x 7): radiation is 1/100th
• At 2 weeks (343 hours): radiation is 1/1,000th

FEMA's planning guidance states that fallout radiation drops to roughly 1% of peak levels within 48 hours. The most dangerous period is the first 24 hours. If you shelter effectively through that window, your cumulative exposure drops dramatically.

For areas directly downwind of a detonation, plan on 14 to 28 days of sheltering before outdoor activity becomes advisable. For areas farther from the blast zone, the timeline compresses to 3 to 7 days. These figures come from FEMA's 72-Hour Nuclear Detonation Response Guidance document.

Shelter Protection Factors

Not all shelters are equal. Protection is measured by a Protection Factor (PF) — the ratio by which a structure reduces radiation exposure.

• Open air: PF 1 (no protection)
• Wood-frame house, single story: PF 2 to 3
• Concrete or brick building, upper floors: PF 10 to 20
• Concrete or brick building, basement: PF 40 or higher
• Below-grade parking garage or underground structure: PF 100 to 200
• Purpose-built fallout shelter with 3 feet of packed earth: PF 200 to 1,000

A standard residential basement in a brick home provides a PF of approximately 40, meaning you receive 1/40th of the outside radiation dose. According to FEMA's shelter assessment data, this level of protection is sufficient to survive even heavy fallout conditions if you remain sheltered for the first 48 hours.

The three factors that determine shelter quality are shielding (mass of material between you and fallout), distance (how far you are from the fallout particles on roofs and ground), and time (how long you wait for decay to reduce levels).

Improving Your Existing Shelter

If you have a basement, you can increase its PF with materials already in your home:

• Stack books, filled bookshelves, or file cabinets against exterior walls
• Move furniture and heavy objects to the floor above the shelter area (adds mass overhead)
• Fill trash cans, buckets, or bathtubs with water and position them along walls (water is a good radiation absorber — 1 gallon weighs 8.34 pounds)
• Block basement windows with sandbags, concrete blocks, or even bags of soil from the yard

Each additional inch of concrete provides roughly 40% more shielding. Six inches of concrete or 8 inches of packed earth will halve your radiation exposure.

The Supply List

The Federal Emergency Management Agency recommends a minimum 72-hour preparedness kit for all hazards. For nuclear scenarios specifically, plan for 14 days minimum. Here is the supply list, broken into tiers.

Tier 1: Minimum 72-Hour Kit

• Water: 1 gallon per person per day. For a family of four, that is 12 gallons for 72 hours. FEMA lists this as the single highest priority supply item across all disaster types.
• Food: Non-perishable items requiring no cooking — canned goods, protein bars, dried fruit, peanut butter. Approximately 2,000 calories per person per day.
• Battery-powered or hand-crank AM/FM radio. After a nuclear event, the Emergency Alert System and NOAA Weather Radio will be the primary channels for shelter-in-place updates and evacuation orders.
• Flashlight and extra batteries
• First aid kit
• Prescription medications: 14-day supply minimum
• Dust masks or N95 respirators (filtering airborne fallout particles)
• Plastic sheeting and duct tape (for sealing windows and vents)
• Garbage bags and plastic ties (sanitation)
• Wrench or pliers (to turn off utilities)

Tier 2: Extended 14-Day Kit

• Additional water: total of 56 gallons for a family of four. This is the hard part — 56 gallons weighs 467 pounds. Water storage containers rated for long-term storage solve the logistics.
• Water purification: filters rated to 0.2 microns or smaller, plus unscented liquid chlorine bleach (8 drops per gallon for purification, per EPA guidelines)
• Potassium iodide (KI) tablets: the FDA recommends KI to block radioactive iodine uptake by the thyroid. Dosage for adults is 130 mg per day, started within 3 to 4 hours of exposure for maximum effectiveness. KI does not protect against other radioactive isotopes.
• Expanded food supply: freeze-dried meals, rice, beans, canned meats
• Manual can opener
• Sanitation supplies: 5-gallon bucket with snap-on toilet lid, heavy-duty trash bags, cat litter or lime for waste treatment
• Fire extinguisher
• Battery bank or solar charger
• Change of clothing and sturdy shoes per person
• Copies of identification documents, insurance policies, and financial records in a waterproof container

Tier 3: Reference and Communication

• Printed reference materials: nuclear detonation response procedures, first aid manuals, water purification methods, and shelter improvement diagrams. In a nuclear event, telecommunications infrastructure will be degraded or destroyed. Cell towers, internet service, and landlines within the affected zone will be offline. Any reference material you need must already be in your possession.
• The Deadnet USB drive was built specifically for this gap — it contains 19 military and government source documents including Army field manuals and medical references, plus a local AI assistant that runs without internet, cell service, or cloud connectivity.
• Two-way radios (FRS/GMRS) with spare batteries for short-range communication
• Whistle for signaling

Potassium Iodide: What It Does and Does Not Do

There is widespread misunderstanding about KI tablets. Here is what the CDC and FDA have published:

KI protects only the thyroid gland, and only from radioactive iodine (I-131), which is one of many isotopes produced by a nuclear detonation or reactor meltdown. It does not protect against external radiation, other radioactive isotopes (cesium-137, strontium-90), or blast effects.

The FDA-approved dosage schedule:

• Adults over 18: 130 mg
• Children 3 to 18: 65 mg
• Children 1 month to 3 years: 32 mg
• Newborns to 1 month: 16 mg

Timing matters. KI is most effective when taken within 3 to 4 hours before or after exposure to radioactive iodine. Taken 24 hours after exposure, effectiveness drops significantly.

KI is available over the counter in the US. The Nuclear Regulatory Commission provides free KI to populations within 10 miles of operating nuclear power plants — nearly 3 million Americans live within that radius, according to NRC data.

Do not take KI unless directed by public health authorities or unless you have direct knowledge of a nuclear release. Unnecessary use can cause thyroid complications, particularly in people over 40.

Radiation Monitoring

Without a way to measure radiation, you are operating blind. Two tools matter:

• Dosimeter: measures your cumulative radiation exposure. This tells you how much total radiation your body has absorbed. A reading above 100 rem indicates radiation sickness symptoms are likely. Above 300 rem is life-threatening without medical intervention.
• Survey meter (Geiger counter): measures current radiation levels in your environment. This tells you whether it is safe to leave shelter, which routes have lower contamination, and whether food or water sources are contaminated.

Basic Geiger counters are available commercially for $150 to $400. For a household preparedness kit, even an entry-level unit provides data that is orders of magnitude better than guessing.

If you do not have monitoring equipment, follow the time-based sheltering guidelines from FEMA: remain sheltered for a minimum of 24 hours, preferably 48 to 72 hours, before any outdoor exposure. Limit initial outdoor trips to 30 minutes or less.

Decontamination Procedures

If anyone in your group was outdoors during fallout:

1. Remove all outer clothing before entering the shelter. Removing clothing eliminates up to 90% of external contamination, according to the CDC's radiation emergency guidelines.
2. Bag the contaminated clothing in plastic and leave it outside the shelter area.
3. Shower or wash with soap and warm water. Do not scrub hard — you will damage skin and drive particles into abrasions. Wash hair with shampoo only, not conditioner (conditioner binds particles to hair).
4. Blow nose, wipe eyelids and ears with a damp cloth.
5. Put on clean clothing.

If water is limited, a dry decontamination with clean towels or wet wipes is better than nothing. The priority is removing fallout particles from skin and hair.

Communications After a Detonation

The electromagnetic pulse (EMP) from a nuclear detonation will disable most unshielded electronics within a radius that depends on altitude and yield. A surface burst produces a localized EMP; a high-altitude burst (above 25 miles) can affect electronics across hundreds of miles.

What will likely still work:

• Battery-powered AM/FM radios (simple analog circuits are more EMP-resistant)
• Hand-crank radios
• FRS/GMRS two-way radios (if shielded or outside the EMP radius)
• Vehicle radios (vehicles provide partial EMP shielding)

What will likely be down:

• Cell networks (towers require grid power and backhaul)
• Internet (backbone infrastructure in the affected area will be offline)
• Landlines (exchanges require power)

The Emergency Alert System is designed to function through EMP events via hardened broadcast infrastructure. An AM/FM radio is your primary link to official information. Keep one with fresh batteries in your shelter supplies at all times.

For your reference materials and any digital information you need, store it on devices kept in a Faraday bag or enclosure when not in use. The Deadnet drive, for instance, pairs well with a small laptop stored in an EMP-protective bag — giving you access to medical references, field manuals, and an AI assistant even after communications infrastructure is gone.

What to Do Today

Do not try to assemble a complete 14-day kit in one trip. Start with one action:

Buy a case of bottled water (3 to 5 gallons) and put it in your basement, closet, or lowest interior room. That single step puts you ahead of the roughly 48% of American households that FEMA's National Household Survey found do not have supplies set aside for a 3-day emergency. Next week, add a battery-powered AM radio and a pack of N95 masks. Build the kit one layer at a time, starting with water, then communications, then food, then medical supplies. The supply list above gives you the full target — work toward it at whatever pace your budget allows.