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

On April 13, 2026, FEMA announced a radiological emergency preparedness exercise at the Peach Bottom Atomic Power Station in Pennsylvania and Maryland, scheduled for the week of April 27. That same week, the agency approved disaster declarations across seven states for unrelated events. The federal apparatus is stretched. If a nuclear incident occurred tomorrow, your survival in the first 72 hours would depend almost entirely on what you knew and had on hand before it happened.

This guide covers what the federal planning documents actually say about nuclear survival, stripped of both the Hollywood panic and the bureaucratic hedging. The physics of fallout are straightforward. The actions that save lives are specific and learnable.

The 72-Hour Window: Why Timing Is Everything

FEMA's Nuclear Detonation Response Guidance establishes the first 72 hours as the planning horizon for a reason: roughly 90% of dangerous fallout radiation decays within that window. The most lethal period is the first 1-2 hours after detonation, when radiation intensity is highest. After 7 hours, radiation drops to about one-tenth of its initial level. After 49 hours, it drops to one-hundredth.

This decay curve is governed by the Wayson Rule (also called the 7-10 Rule): for every sevenfold increase in time after detonation, radiation intensity drops by a factor of 10. This is not an approximation. It is a consistent physical property of fission product decay.

What this means practically: if you can shelter adequately for 24 to 72 hours, you will have outlasted the most dangerous phase. The longer you stay sheltered, the lower your cumulative dose. FEMA's shelter-in-place guidance states that people should remain sheltered for at least 24 hours unless told otherwise by authorities, with some scenarios requiring shelter for up to one month.

Shelter: Your Single Highest-Value Preparation

A 2010 federal exercise called Operation Golden Phoenix modeled a nuclear detonation in Los Angeles. The finding: 285,000 people would die or develop acute radiation sickness. But 84% of those casualties could be prevented if people simply moved to basements and interior rooms. That is not a theoretical number. It came from detailed casualty modeling by Lawrence Livermore National Laboratory.

The concept that matters here is Protection Factor (PF) — how much a structure reduces radiation exposure compared to standing in the open. FEMA TR-87 sets PF 40 as the minimum standard for public fallout shelters, meaning radiation inside is reduced to 1/40th of the outside level.

Here is what common structures actually provide:

• A wood-frame house with no basement: PF 2-3 (reduces radiation by half to two-thirds)
• A typical house: PF 15 (reduces to 1/15th)
• A basement with earth-covered walls: PF 100-300 (depending on construction)
• A concrete office building, interior rooms: PF 50-200
• A purpose-built shelter with 24 inches of concrete: PF 1,000

The takeaway: a basement is adequate shelter for the first 72 hours in most fallout scenarios. If you live in a wood-frame home without a basement, identify the nearest concrete or brick building you could reach in under 10 minutes.

Improvised Shelter Improvements

You do not need a bunker. You need mass between you and the fallout particles that have settled on surfaces outside. According to Nuclear War Survival Skills by Cresson Kearny (originally published by Oak Ridge National Laboratory), the following materials reduce gamma radiation by half per listed thickness:

• Packed earth or sand: 3.6 inches per halving
• Concrete: 2.2 inches per halving
• Steel: 0.7 inches per halving
• Wood: 8.8 inches per halving
• Water: 4.8 inches per halving

If you are sheltering in a basement, stacking bags of soil, sand, or even water containers against above-ground walls and around windows adds meaningful protection. Two feet of earth against a basement wall with boarded windows yields a protection factor of several hundred, according to FEMA's Fallout Protection for Homes with Basements guide.

The Supply List: 72 Hours Minimum, 14 Days Preferred

The Red Cross and FEMA both recommend a minimum 72-hour kit, but their own planning documents model scenarios requiring 14 to 30 days of sheltering. Build for 14 days. Here is what that requires per person:

Water

• 1 gallon per person per day for drinking and sanitation (CDC standard)
• 14-day supply: 14 gallons per person
• For a family of four: 56 gallons
• Store in food-grade containers away from direct sunlight
• Water purification tablets or a gravity filter as backup

Food

• 2,000 calories per person per day (USDA baseline for moderate activity)
• Canned goods, freeze-dried meals, energy bars, peanut butter, crackers
• No-cook options only — assume you cannot safely ventilate cooking fumes
• Manual can opener (this item is forgotten in approximately 40% of emergency kits, per a 2023 FEMA community preparedness survey)

Radiation-Specific Supplies

• Potassium iodide (KI) tablets: 130mg for adults, 65mg for children 3-18. The CDC reports that KI taken within 1-2 hours of radioactive iodine exposure blocks more than 90% of thyroid uptake. After 4 hours, effectiveness drops significantly. KI is available over-the-counter and has a shelf life of approximately 7 years when stored properly.
• N95 masks or better: reduces inhalation of fallout particles
• Plastic sheeting and duct tape: for sealing windows and doors against particulate infiltration
• Change of clothes in sealed bags: outer clothing worn during fallout exposure should be removed and bagged before entering shelter

Information and Communication

• Battery-powered or hand-crank AM/FM radio with NOAA Weather Radio capability
• Extra batteries (lithium cells have a 20-year shelf life vs. 5-10 years for alkaline)
• A written list of emergency broadcast frequencies for your area
• Copies of family emergency plans and meeting locations

A USB drive loaded with offline reference material — including military field manuals, medical guides, and survival documentation — gives you a reference library that does not depend on cell towers or internet infrastructure. Deadnet's offline AI survival drive, for example, carries 19 government and military source documents alongside a local AI assistant that runs without any network connection, which is the kind of resource that earns its weight in a shelter scenario where your phone is a paperweight.

Potassium Iodide: What It Does and Does Not Do

KI is one of the most misunderstood items in nuclear preparedness. It protects exactly one organ (the thyroid) from exactly one isotope (radioactive iodine, I-131). It does nothing against other radioactive materials, external gamma radiation, or blast effects.

The FDA-approved dosing by age:

• Adults over 18 through 40: 130 mg
• Children 3-18: 65 mg
• Children 1 month to 3 years: 32 mg
• Newborns birth to 1 month: 16 mg

Adults over 40 should generally not take KI unless expected thyroid doses are very high, as the risk of KI side effects increases with age while thyroid cancer risk from radiation decreases.

One dose protects for 24 hours. Do not take more than recommended — the CDC states that higher doses do not provide additional protection and can cause severe illness or death. Take KI only when instructed by public health officials or when you have direct knowledge of radioactive iodine release.

Fallout: What It Is and How It Behaves

Fallout is not invisible poison gas. It is physical particulate — irradiated dust and debris pulled into the mushroom cloud, which then settles back to earth downwind of the detonation. It looks like sand or fine ash. It behaves like sand or fine ash. It settles on horizontal surfaces: roofs, cars, the ground.

The fallout pattern depends on wind speed, wind direction, and detonation yield. FEMA's Nuclear Device City Planner Resource (nucCPR) models show that a 10-kiloton ground burst — the size intelligence agencies consider most likely for a terrorist device — produces a fallout plume extending 10-20 miles downwind under typical weather conditions.

Key fallout behaviors:

• Heavier particles settle first, closer to the blast (within 1-2 hours)
• Lighter particles travel farther downwind and settle over 24+ hours
• Rain accelerates fallout deposition (if it is raining, get inside faster)
• Fallout does not penetrate intact skin — the danger is inhalation and ingestion
• Removing outer clothing and showering removes approximately 90% of external contamination (FEMA shelter-in-place guidance)

If you are caught outside when fallout begins, cover your nose and mouth, do not touch the fallout material, get inside the nearest solid structure, remove your outer clothing before entering living space, and shower or wipe down exposed skin with wet cloths.

Blast Zones: Know Your Distance

Not all nuclear threats are equal. The federal government primarily plans for two scenarios:

Scenario 1 — A 10-kiloton improvised nuclear device (terrorist threat). This is the scenario modeled in most current federal planning documents. The immediate blast destruction radius is approximately 0.5 miles. Severe damage extends to about 1 mile. The thermal flash causes burns at up to 1.5 miles. Fallout is the primary danger beyond 1.5 miles.

Scenario 2 — A strategic warhead in the 100-800 kiloton range. Immediate destruction extends 2-5 miles from ground zero. Severe structural damage reaches 5-10 miles. Fallout becomes a continental-scale concern.

A study from the University of Nicosia published in Physics of Fluids found that people located 2-7 miles from a detonation zone can survive the blast wave if properly sheltered. The key variable is not distance alone — it is whether you are inside a reinforced structure when the shockwave arrives.

If you see a flash: do not go to the window. Get to an interior room or basement. The shockwave travels slower than light — you may have seconds to tens of seconds depending on your distance. Lie flat, face down, and cover your head.

Communication and Information After Detonation

A nuclear detonation will likely disable cell networks through a combination of electromagnetic pulse effects, tower damage, and network overload. FEMA's communication guidance for the immediate aftermath assumes that normal communication infrastructure will be unavailable.

What may still work:

• AM radio (longer range, more resilient infrastructure)
• NOAA Weather Radio (dedicated broadcast system with backup power)
• CB radio and FRS/GMRS handheld radios (for local communication)
• Ham radio (if you are licensed and equipped)

What will almost certainly not work:

• Cell phones (network overload and possible tower damage)
• Internet (infrastructure dependent on functioning power grid and routing)
• Landlines (may work in some areas but unreliable)

This is where offline information becomes a survival resource rather than a convenience. Any reference material stored on your phone that requires a network connection is inaccessible. Physical field manuals, printed reference cards, and offline digital libraries on USB drives are the backup that actually functions. Deadnet was designed for exactly this scenario — when the network is down and you need to reference a military field manual or medical guide without waiting for a signal that is not coming.

The Switzerland Standard

Switzerland requires by law that all residential buildings constructed after 1978 contain a nuclear shelter capable of withstanding a 12-megaton blast at 700 meters. The country maintains shelter capacity for 114% of its population — more shelter spaces than people.

The United States has no equivalent program. The federal shelter survey program was defunded in the 1980s. Current FEMA guidance places the responsibility for shelter identification on state and local jurisdictions, most of which have not conducted shelter surveys since the Cold War.

This means shelter planning is your responsibility. Walk your neighborhood. Identify concrete and brick structures within a 10-minute walk. Know which buildings have basements. Have a primary and secondary shelter location. Tell your family where to go if they cannot reach home.

Your Next Step

Today, not this week, walk through your home and identify your best shelter location. It is likely a basement corner away from windows, or an interior closet on the lowest floor. Measure the wall thickness. Count the number of barriers between that spot and the outside. Then put 1 gallon of water and a battery-powered radio in that location. You have just completed the single action with the highest return on effort in nuclear preparedness: you have a shelter location your family knows about, with the two supplies that matter most in the first 24 hours. Build out from there.