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 89 seconds to midnight — the closest it has ever been. The New START treaty expired in February 2026 with no replacement framework in negotiation. Russia, China, and the United States are simultaneously modernizing their nuclear delivery systems.

None of this means a nuclear event is imminent. It means the margin for error is thinner than it has been in decades, and the window between a warning and a detonation could be as short as 15 to 30 minutes for an ICBM strike. That is not enough time to learn what to do. It is enough time to execute a plan you already have.

This guide covers what you need to know, what you need to have, and what you need to do — broken into the three phases that matter: before, during, and after.

Understanding the Threat

Not all nuclear scenarios are the same, and your response depends on the type of event.

A strategic nuclear strike involves warheads in the hundreds-of-kilotons range delivered by ICBMs or submarine-launched ballistic missiles. FEMA's Radiological Emergency Preparedness program models these as producing blast radii of 1 to 5 miles of total destruction, with thermal radiation burns extending 10 miles or more depending on yield and weather conditions.

A tactical or "limited" nuclear exchange involves smaller warheads, typically under 10 kilotons, deployed on shorter-range systems. The blast and fallout zones are significantly smaller but still lethal within a mile or more.

A nuclear accident — reactor meltdown, transportation incident, or dirty bomb — produces no blast wave but can disperse radioactive material over a wide area. The NRC tracks 93 operating commercial reactors across 54 sites in the United States. If you live within 10 miles of a reactor, your local government is required to have an evacuation plan on file.

An electromagnetic pulse (EMP) from a high-altitude detonation is a separate category. A single warhead detonated at 250 miles altitude could affect electronics across the continental United States. This scenario has significant overlap with grid-down preparedness.

The point is not to predict which scenario is most likely. It is to understand that your preparations cover a range of events, not a single Hollywood version.

Shelter: Your First and Best Defense Against Fallout

Fallout is the primary killer after the initial blast. Radioactive particles carried by wind begin settling within 15 to 30 minutes of detonation. FEMA guidance is clear: get inside, stay inside, stay tuned.

The Protection Factor (PF) of a structure measures how much it reduces your radiation exposure. Here is how common structures compare, based on FEMA's planning guidance:

• A wood-frame house offers a PF of 2 to 3, meaning it cuts exposure by roughly half to two-thirds. This is minimal.
• A basement in a wood-frame house provides a PF of 10 to 20.
• A concrete or brick building with no windows offers a PF of 40 or higher.
• A basement of a large concrete structure can exceed a PF of 200.
• Purpose-built fallout shelters were designed for PF 40 to 1,000.

What this means practically: if you are in a wood-frame house on the first floor during heavy fallout, you are absorbing roughly half the outdoor radiation dose. In a concrete basement, you are absorbing 1/200th. The difference between those two positions could be the difference between acute radiation sickness and no symptoms at all.

Walk through your home and workplace right now. Identify the room with the most mass between you and the outside: basement corners, interior rooms, spaces below grade. That is your shelter-in-place location. Mark it mentally.

If you have no basement, move to the center of the building, away from windows and exterior walls. Stack furniture, books, bags of soil — anything with density — between you and the outside walls. Every inch of material reduces exposure.

The 48-Hour Supply Kit

FEMA recommends sheltering in place for a minimum of 24 hours after a nuclear detonation, though 48 to 72 hours is more realistic based on fallout decay patterns. The "7-10 rule" of radiation decay states that for every sevenfold increase in time after detonation, radiation intensity drops by a factor of 10. After 49 hours (7 times 7 hours), outdoor radiation is approximately 1/100th of the 1-hour level.

Your kit needs to sustain your household for at least 72 hours with no outside contact.

Water: 1 gallon per person per day, minimum. A family of four needs 12 gallons for 72 hours. Store this in your shelter location, not in the garage you will not be able to access. If your stored water runs out, the safest sources are sealed pipes and hot water heaters already inside the structure. Do not collect rainwater during active fallout.

Food: Shelf-stable, no-cook items. Canned goods, energy bars, peanut butter, dried fruit, crackers. You will not have reliable power for cooking. A manual can opener is not optional.

Medication: A 7-day supply of all prescription medications for every household member. OTC pain relievers, anti-diarrheal medication, and electrolyte packets.

Potassium Iodide (KI): The FDA has approved KI as a thyroid-blocking agent for radioactive iodine exposure. The standard adult dose is 130 mg, taken once daily for the duration of exposure risk. KI only protects the thyroid and only against radioactive iodine — it does not protect against other isotopes. It is available over the counter and costs under $15 for a 14-day supply. Keep it with your kit.

Sanitation: Plastic bags, a bucket with a lid, disinfectant, and toilet paper. If you are sheltering for 72 hours, you need a sanitation plan. This is the item people forget until they need it.

Communication: A battery-powered or hand-crank AM/FM/NOAA radio. After a nuclear event, official guidance on fallout patterns, evacuation corridors, and all-clear announcements will come through the Emergency Alert System. Cell towers may be down. Internet may be unavailable. Your radio is your lifeline. Stock extra batteries.

The Deadnet USB drive includes the full text of FM 3-11 (CBRN Operations), TC 3-10 (Commander's Handbook for CBRN), and other military CBRN references. Having these documents available offline and searchable through a local AI means you can look up decontamination procedures, radiation exposure thresholds, and protective action guidelines without any network connection — which is exactly the scenario a nuclear event creates.

Radiation Basics You Need to Internalize

You do not need a physics degree. You need a few numbers.

Radiation exposure is measured in roentgens (R) or sieverts (Sv). For emergency planning, most U.S. guidance uses rem (roentgen equivalent man) or its metric equivalent, millisieverts (mSv). 1 rem equals 10 mSv.

According to CDC data on acute radiation syndrome thresholds:

• Below 100 rem (1 Sv): No immediate symptoms in most people. This is the range where long-term cancer risk increases modestly.
• 100 to 200 rem: Nausea and fatigue within hours. Most people recover.
• 200 to 400 rem: Severe illness. Medical treatment significantly improves survival.
• Above 400 rem: Fatal without aggressive medical intervention. Above 600 rem, fatality rate approaches 100%.

Context: the average American receives about 0.62 rem (6.2 mSv) per year from natural background radiation, per the National Council on Radiation Protection.

The practical takeaway is that every hour you spend in a high-PF shelter during the first 48 hours dramatically reduces your cumulative dose. Staying in a PF-40 shelter for 48 hours instead of standing outside could mean the difference between 10 rem exposure and 400 rem exposure in a moderate fallout zone.

If you have access to a dosimeter or radiation detection card, keep it in your kit. Survey meters (CDV-700 series) can sometimes be found surplus for under $50. They are old civil defense equipment and still functional.

Evacuation Versus Shelter-in-Place

The default recommendation from FEMA and ORISE (Oak Ridge Institute for Science and Education) is to shelter in place immediately after detonation. You do not know the fallout pattern. You do not know wind direction at altitude. You do not know if more detonations are coming.

Evacuation becomes the correct choice under specific conditions:

• Your structure has a PF below 10 and a better shelter is within 15 minutes of travel
• You are in a confirmed blast damage zone and your structure is compromised
• Authorities issue an evacuation order after the initial 24-hour shelter period, based on confirmed fallout mapping

If you evacuate, the National Nuclear Security Administration (NNSA) recommends moving perpendicular to the wind direction. Fallout patterns are elliptical, extending downwind from the detonation point. Moving crosswind gets you out of the plume fastest.

Have two evacuation routes planned to locations at least 50 miles from any likely target. FEMA's National Risk Index identifies the highest-risk areas based on population density, military installations, and infrastructure. Review it for your area.

Keep a go-bag in your vehicle with 72 hours of supplies, copies of critical documents, cash in small bills, a regional road map (not GPS-dependent), and a full change of clothes in a sealed bag for each family member. The sealed clothing matters — you may need to strip and change after moving through a contaminated area.

Decontamination

If you were outside during fallout or traveled through a contaminated area, decontamination is straightforward but non-negotiable.

The process, per FEMA's radiological decontamination guidelines:

1. Remove all outer clothing. This single step eliminates up to 90% of external contamination, according to CDC guidance on radiation emergencies.
2. Place removed clothing in a plastic bag and seal it. Leave it outside your shelter.
3. Shower with warm water and soap. Do not scrub hard — you will open pores and push particles into the skin. Do not use conditioner, as it binds radioactive particles to hair.
4. Blow your nose, wipe eyelids and ears with a damp cloth.
5. Put on clean, uncontaminated clothing.

If water is limited, wipe down with wet cloths or unscented baby wipes, focusing on exposed skin and hair. The goal is removing particles, not sterilization.

Communications Plan

Assume cell networks are down. Assume the internet is unavailable. Assume landlines are overloaded or damaged.

Before an event occurs, establish with your household:

• A primary and secondary meeting location
• An out-of-area contact person everyone calls to check in (long-distance lines often work when local lines are jammed — this is FEMA's standard family communication plan recommendation)
• A physical message drop location (a specific tree, mailbox, or wall where a note in a zip bag can be left)
• Agreed-upon radio frequencies if anyone has handheld radios (FRS/GMRS radios are under $30 per pair)

Write this plan down on a card. Each family member carries a copy. Phones may be dead. Memory under stress is unreliable. The card works.

Deadnet's offline AI assistant can help you draft a household communications plan template and customize it to your specific area, even without connectivity. Having the ability to query reference material and generate structured plans on a device that fits in your pocket fills a gap that paper manuals alone cannot.

Long-Term Considerations

If a nuclear event is not a single isolated detonation — if it is part of a broader exchange — the situation extends well beyond 72 hours. Food supply chains will stop. Power grids may be down for weeks or months. Medical facilities will be overwhelmed.

NOAA's National Centers for Environmental Information has tracked 376 billion-dollar weather and climate disasters in the United States since 1980, totaling $2.665 trillion in cumulative costs. A nuclear event would dwarf any of these. The Federal Reserve's 2023 Economic Well-Being report found that 37% of American adults could not cover an unexpected $400 expense. Extended disruption would create cascading failures in food, water, medical, and financial systems simultaneously.

Long-term preparedness means:

• A 30-day food supply, minimum, stored in your shelter location
• Water filtration capability (not just stored water)
• Knowledge of food production, foraging, and preservation
• Medical training beyond basic first aid
• A network of trusted neighbors and community contacts
• Physical copies of reference material covering agriculture, medicine, mechanical repair, and sanitation

No one person can store or know everything. Community resilience matters more than individual stockpiles when the timeline extends past a few weeks.

Your Next Step

Do one thing today: identify the highest-PF room in your home. Walk to it. Time how long it takes you to get there from your most common locations — bed, kitchen, office. Decide where in that room your 72-hour kit will live. Then fill a single container with 3 gallons of water and put it there.

That is not everything. But it is the single action that saves the most lives in the first hours, and it costs nothing but 10 minutes of your time. Everything else builds on having a shelter location selected and minimally supplied. Start there. Build out from there.