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. The New START treaty between the United States and Russia expired in February 2026, ending the last bilateral arms control agreement between the two largest nuclear powers. India and Pakistan entered a four-day military crisis in May. China continues expanding its warhead stockpile. The Arms Control Association now describes the current environment as a "full-blown arms race no longer limited to two superpowers."

This is not a theoretical exercise. This is a planning document for a scenario that defense analysts assign increasing probability to each year. The information below is drawn from FEMA nuclear detonation response guidance, Department of Health and Human Services planning documents, and Ready.gov shelter-in-place protocols.

The First 10 Minutes: What Happens and What You Do

A nuclear detonation produces three immediate effects: a thermal pulse, a blast wave, and an electromagnetic pulse. If you see a flash brighter than anything you have experienced, you are alive and within survivable range. What you do in the next 10 minutes determines whether you stay that way.

FEMA's Planning Guidance for Response to a Nuclear Detonation states that you will have approximately 10 minutes or more before radioactive fallout begins arriving at ground level. This is your action window.

Your priorities in order:

1. Get inside the nearest solid structure. Brick, concrete, or stone walls. A basement is ideal. A multi-story building's interior rooms work. A wood-frame house is better than being outside but offers minimal protection.
2. Move to the center of the structure, as far from exterior walls and the roof as possible.
3. If you are in a car, it offers almost no protection. Abandon it and get into a real building.
4. Do not look at the fireball. Do not go to windows. The blast wave follows the flash by seconds to minutes depending on your distance.

If you are within 10 to 25 miles of the detonation, fallout particles roughly the size of table salt or sand will begin settling on every exposed surface — the ground, rooftops, vehicles, and anyone still outside.

Understanding Radiation: The Numbers That Matter

Radiation from fallout follows a decay curve described by the 7:10 rule. For every 7-fold increase in time after detonation, the radiation intensity drops by a factor of 10.

In practical terms:

• At 7 hours after detonation, radiation is 1/10th of its initial level
• At 49 hours (about 2 days), it is 1/100th
• At 2 weeks, it is approximately 1/1,000th — about 1% of the original intensity

This decay curve is why the first 24 hours are the most dangerous and why shelter-in-place is the single most effective survival action. According to FEMA, adequate shelter reduces radiation exposure by a factor of 10 to 200 depending on building type. A concrete basement provides a protection factor of approximately 200, meaning you receive 1/200th of the outdoor radiation dose.

The unit you need to know is the rem (or its metric equivalent, the sievert). The CDC identifies 100 rem as the threshold for acute radiation sickness symptoms. Below 25 rem, most people show no clinical symptoms. Your goal is to minimize total accumulated dose during the first 48 hours, when ambient radiation is highest.

Shelter Selection: Rating Your Options

Not all buildings provide equal protection. FEMA assigns protection factors (PF) to different structure types:

• Concrete basement, 3+ feet underground: PF 200 or higher
• Middle floors of a concrete high-rise: PF 100-200
• Ground floor of a concrete building: PF 40-100
• Brick house basement: PF 20-50
• Wood-frame house, no basement: PF 2-5
• Vehicle: PF 2-3
• Outdoors: PF 1 (full exposure)

If you are in a low-PF structure when fallout begins and a higher-PF structure is within a 5-minute sprint, move to it. If it is farther than 5 minutes away, stay where you are and improve your current shelter. Every minute outside during active fallout accumulates dose.

To improve a wood-frame house:

• Move to the most interior room on the lowest floor
• Stack books, furniture, water containers, and any dense material against exterior walls
• Block windows with mattresses, heavy curtains, or filled garbage bags
• Seal gaps around doors and windows with wet towels or tape to reduce dust infiltration
• If you have a crawl space, placing dirt or sandbags on the floor above you adds shielding

The HHS Nuclear Detonation Planning Guide notes that improvised shielding using common household materials can meaningfully increase a structure's protection factor if the materials are dense and placed between you and exterior surfaces.

The 24-Hour Shelter Period

FEMA guidance is direct: remain in the most protective location for the first 24 hours unless an immediate hazard — fire, gas leak, structural collapse, or a life-threatening injury — forces you to move. In heavy fallout zones, this period may extend to 72 hours or longer.

During shelter-in-place:

• Turn off HVAC systems that draw air from outside. Forced air heating and central air conditioning pull contaminated particles indoors.
• Seal the room you are in. Tape plastic sheeting over windows and vents if available.
• If you were outside during fallout, remove all outer clothing before entering the shelter area. Bag the clothing and leave it outside your occupied space. Shower or wipe down exposed skin with wet cloths. This alone removes up to 90% of external contamination, according to Ready.gov.
• Ration water starting immediately. Assume taps may stop working within hours. Any water that was in sealed containers before the event is safe to drink. Open water sources may be contaminated.
• Monitor battery-powered or hand-crank radio for emergency broadcasts. FEMA's Emergency Alert System and NOAA Weather Radio are the primary channels for official guidance on when to evacuate or continue sheltering.

Supply Planning: What to Have Before It Happens

The Red Cross and FEMA both recommend a minimum 72-hour supply kit, but for nuclear scenarios, two weeks of supplies is the realistic planning target based on the fallout decay timeline.

Water: One gallon per person per day. For two weeks, that is 14 gallons per person. A family of four needs 56 gallons. This is approximately four standard 55-gallon drum's worth for the household, or more practically, a combination of stored water jugs and a gravity-fed filter for supplementing from questionable sources.

Food: Non-perishable, calorie-dense, requiring minimal or no water to prepare. Canned goods, peanut butter, dried fruit, energy bars, freeze-dried meals. The USDA estimates an adult needs approximately 2,000 calories per day at rest. Under stress, the number rises, but rationing may be necessary.

Medical supplies: A standard first aid kit plus potassium iodide (KI) tablets. The FDA has approved KI for thyroid protection during radiation emergencies. It must be taken within hours of exposure to be effective — it blocks the thyroid from absorbing radioactive iodine-131, which is a major component of fresh fallout. The CDC recommends 130 mg for adults, 65 mg for children ages 3-18. KI does not protect against other types of radiation. It protects one organ from one isotope. Do not treat it as a general radiation cure.

Additional items:

• Battery-powered or hand-crank radio (NOAA frequencies)
• Flashlights and spare batteries
• Plastic sheeting and duct tape for room sealing
• N95 or P100 respirator masks (reduces inhaled particle contamination)
• Heavy-duty garbage bags for contaminated clothing disposal
• Wrench or pliers for shutting off gas lines
• Printed reference materials — field manuals, first aid guides, radiation dose charts

That last item deserves emphasis. In a nuclear event, cell towers will be overloaded or destroyed, internet connectivity will be unreliable or nonexistent, and GPS satellites may be affected by EMP effects. Any reference material you depend on needs to exist in a format that works without infrastructure. The Deadnet USB drive carries 19 military and government source documents including field medical references and survival manuals accessible entirely offline through a local AI assistant — the kind of resource that has zero dependency on networks or power grids beyond the device you plug it into.

Communications Planning

Assume your phone will not work normally. Cell networks will be overloaded within minutes of a detonation, and towers within the blast radius will be destroyed. The 2011 earthquake and tsunami in Japan saw cell network failures lasting days despite no nuclear event — an actual detonation compounds this by orders of magnitude.

Your backup communication options:

• AM/FM radio for receiving emergency broadcasts. AM signals travel farther and penetrate buildings better than FM.
• NOAA Weather Radio on frequencies 162.400 to 162.550 MHz. Dedicated weather radio receivers cost under $30 and run on batteries.
• FRS/GMRS handheld radios for local communication within a 1-2 mile range. These do not require a license for FRS channels.
• HAM radio if you have a license and equipment. HAM operators historically provide critical communication links when all other infrastructure fails. FEMA's Auxiliary Communications program relies on volunteer HAM operators during disasters.

Have a pre-arranged meetup location and a communication plan with family members that does not depend on phones or internet. A physical card in each family member's wallet with the address, a backup address, and the name of an out-of-state contact works when nothing electronic does.

Evacuation vs. Shelter: Making the Call

The default is shelter-in-place for the first 24 hours. Evacuation during active fallout increases your exposure and is nearly always the wrong decision unless your structure is compromised.

After 24-48 hours, the calculation changes. If you are downwind of the detonation site and fallout was heavy, authorities may issue evacuation orders. If no official guidance comes, use these factors:

• Wind direction: Fallout travels downwind. If you are upwind, your contamination levels are lower.
• Distance from detonation: Beyond 25 miles, initial fallout is significantly reduced.
• Shelter quality: If you are in a PF-5 wood-frame house and a PF-100+ concrete structure is reachable within 30 minutes, moving after the first 24 hours may reduce your total dose.
• Medical need: If someone requires care you cannot provide, moving becomes necessary regardless of radiation.

If you evacuate, cover all exposed skin, wear an N95 mask or wet cloth over nose and mouth, and move perpendicular to the wind direction (crosswind) to exit the fallout zone as quickly as possible. Do not move directly upwind — the fallout plume may shift.

Long-Term Considerations

If the event involves a single detonation, the worst contamination will be manageable within 2-4 weeks in most areas. If it involves multiple detonations — a full-scale exchange — the timeline extends and the complexity increases by orders of magnitude.

For the first scenario, your focus shifts from radiation avoidance to resource sustainability: water procurement, food supply chains (which will be disrupted for weeks to months), medical care, and community coordination. The Federal Emergency Management Agency's own post-detonation planning documents acknowledge that government response will be limited in the immediate aftermath, with the first 72 hours primarily relying on individual and community-level self-sufficiency.

Having reference materials you can access without power or internet is not a convenience at this point — it is operational capability. Whether it is printed field manuals, downloaded PDFs on a charged device, or a purpose-built offline reference like Deadnet, the information you can physically access is the information that exists for you.

What to Do Today

Do not treat this as a document to read and set aside. Pick one item from this list and complete it this week:

• Buy 14 days of stored water for your household. Calculate one gallon per person per day.
• Purchase potassium iodide tablets from a pharmacy or online retailer. Verify the dosage matches CDC recommendations (130 mg adult, 65 mg child).
• Identify the three highest-PF structures within a 5-minute walk or drive of your home and workplace. A parking garage, a concrete office building, a school with a basement.
• Put a hand-crank or battery-powered NOAA radio in your supply kit.
• Print or download offline copies of FEMA's nuclear detonation response guidance. If your library of reference material only exists on the internet, it does not exist in the scenario where you need it most.

The Doomsday Clock is at 85 seconds. Arms control frameworks are collapsing. The probability is not zero, and the cost of basic preparation is low. Act on one item today.