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

In January 2026, the Bulletin of the Atomic Scientists moved the Doomsday Clock to 85 seconds to midnight — the closest it has ever been. On February 5, the New START treaty expired, ending the last legally binding limit on U.S. and Russian nuclear arsenals. The WHO is actively updating protocols for nuclear scenarios in the Middle East. None of this is hypothetical anymore. It is planning context.

This guide covers what federal agencies — FEMA, the CDC, and REMM — actually recommend, stripped of bureaucratic padding. The goal is to give you a decision framework and a supply list you can act on this week.

Understanding the Threat Spectrum

Not all nuclear events are the same, and your response changes depending on what you are dealing with.

• A nuclear detonation over a city produces a blast wave, thermal pulse, and radioactive fallout. The blast radius for a 10-kiloton weapon (the size intelligence agencies consider most likely for a terrorist device) extends roughly 0.5 miles for severe damage, with moderate damage out to about 1 mile, according to FEMA's Nuclear Detonation Planning Guide.
• A dirty bomb (radiological dispersal device) spreads radioactive material without a nuclear explosion. The immediate danger zone is far smaller — typically a few city blocks — but contamination can persist.
• A reactor accident, like Fukushima or Chernobyl, produces a slow-moving plume rather than instant fallout. Evacuation timelines are measured in hours to days, not minutes.
• An EMP (electromagnetic pulse) from a high-altitude detonation would not produce significant fallout at ground level but would disable electronics across a wide area.

Your preparations should cover the most demanding scenario — a detonation with fallout — because everything else is a subset of that response.

The 10-Minute Window

FEMA's 72-Hour Nuclear Detonation Response Guidance states that after a detonation, you will have approximately 10 minutes or more before fallout begins arriving at your location, depending on distance and wind. This is your action window.

In those 10 minutes:

1. Do not look at the flash or fireball. The thermal pulse can cause temporary or permanent blindness at distances well beyond the blast zone.
2. Get inside the nearest solid structure. Brick, concrete, and earth are what matter. A concrete basement reduces radiation exposure by a factor of 200 or more. The middle floors of a high-rise building (away from windows and the roof) provide a protection factor of around 10-20. A wood-frame house with no basement provides a factor of 2-3 — better than nothing, but not good.
3. Move to the interior. Put as many walls between you and the outside as possible. Windowless rooms and stairwells in the center of a building are preferred.
4. Seal the space. Close windows, doors, and fireplace dampers. Turn off HVAC systems that pull in outside air. Fallout particles are physical debris — if air is not coming in from outside, neither is fallout.

If you are in a vehicle, do not try to outrun fallout. Drive to the nearest solid building. If no building is reachable in a few minutes, stay in the vehicle with windows up and ventilation off. A car provides a protection factor of roughly 3.

The 7/10 Rule: How Fallout Decays

This is the single most useful piece of nuclear survival knowledge. Radioactive fallout follows a predictable decay curve:

• At 7 hours after detonation, radiation intensity drops to about 10% of the 1-hour level.
• At 49 hours (7 x 7), it drops to about 1% of the 1-hour level.
• At 2 weeks, it is approximately 0.1% of the 1-hour level.

This means the first 24-48 hours are the most dangerous period. According to CDC guidance, you should be prepared to shelter in place for a minimum of 24 hours, and potentially up to 72 hours or longer, depending on fallout intensity in your area. After 48 hours, outdoor exposure becomes significantly more survivable, though caution is still warranted.

The practical takeaway: your shelter needs to sustain you for at least 72 hours without resupply.

Radiation Dose Thresholds

Understanding dose thresholds helps you make informed decisions about when to move, when to stay, and when exposure is acceptable.

According to the Radiation Emergency Medical Management (REMM) database maintained by HHS:

• Below 0.5 Gy (50 rad): No immediate symptoms in most people.
• 1-2 Gy (100-200 rad): Nausea and fatigue within hours. Most people recover fully.
• 2-6 Gy (200-600 rad): Hemopoietic syndrome. Survival depends on medical care and dose. Without treatment, mortality ranges from 0% at the low end to near 100% at the high end.
• Above 6 Gy (600 rad): Survival is unlikely even with medical intervention.

For context, a chest X-ray delivers about 0.0001 Gy. The difference between a survivable dose and a lethal one can be a single wall of concrete between you and the outside.

Building Your Nuclear Preparedness Kit

Your baseline kit should sustain 2-4 people for 72 hours in a sealed shelter environment. This is not a general bug-out bag — it is specifically for sheltering in place during fallout.

Water:

• 1 gallon per person per day, minimum. For a family of four over 72 hours, that is 12 gallons.
• Store in sealed containers. Any water that was indoors and sealed before the event is safe to drink without treatment.
• Water in pipes and hot water heaters is also uncontaminated if it was enclosed during the event.

Food:

• Canned goods, freeze-dried meals, energy bars. Nothing that requires outside water to prepare, ideally.
• FEMA recommends a minimum 3-day supply per person. Calorie targets should be at least 1,200 per person per day for sedentary sheltering — roughly 3,600 calories total per person for the minimum period.

Medical:

• Potassium iodide (KI) tablets. The FDA recommends 130 mg for adults within 3-4 hours of exposure to radioactive iodine. KI does not protect against external radiation — it only prevents the thyroid from absorbing radioactive iodine-131. It is available over the counter.
• A standard trauma first aid kit with added supplies for burns (nuclear detonations produce severe thermal burns at distances far beyond the blast zone).
• Any prescription medications for 2 weeks minimum.

Air filtration:

• N95 or P100 respirators. Fallout particles are physical debris, not gas. A properly fitted N95 provides meaningful protection against inhaling radioactive particulates.
• Plastic sheeting and duct tape for sealing windows and vents if your shelter lacks solid sealing.

Communication:

• A battery-powered or hand-crank AM/FM radio. NOAA Weather Radio and the Emergency Alert System will broadcast shelter-in-place instructions, fallout patterns, and evacuation corridors.
• Do not rely on cell networks. Infrastructure may be destroyed or overwhelmed.

Detection:

• A personal dosimeter or radiation survey meter, if you can source one. Without instrumentation, you are making blind decisions about when it is safe to go outside. Civil defense surplus CDV-715 survey meters are still available and functional.

Sanitation:

• Garbage bags, a 5-gallon bucket with a lid, and cat litter or chemical toilet treatment. With sealed shelter, you cannot go outside for waste disposal.
• Bleach (unscented, 8.25% sodium hypochlorite) for sanitation. One-quarter teaspoon per gallon also purifies water if needed.

Decontamination Procedures

If you were outside during fallout or passed through a contaminated area:

1. Remove outer clothing before entering your shelter. This single step eliminates up to 90% of radioactive contamination, according to CDC guidance.
2. Bag the clothing and leave it outside or in an isolated area.
3. Shower with soap and warm water. Do not scrub skin aggressively — you can create micro-abrasions that allow particles to enter the body. Do not use conditioner on hair, as it binds particles to hair shafts.
4. Blow your nose, wipe eyelids and ears with a damp cloth.
5. If no shower is available, use wet wipes or a damp cloth to wipe exposed skin.

Planning Your Shelter Location

Identify your shelter locations now, not after an event. You need three:

1. Home shelter. Ideally a basement. If you have no basement, identify the most interior room on the lowest floor. Preposition your 72-hour kit there.
2. Workplace shelter. Most commercial buildings have interior rooms, server rooms, or basement levels that work. Know where they are before you need them.
3. Transit shelter. If you commute, identify solid structures along your route — parking garages, concrete commercial buildings, subway stations. You may have less than 10 minutes.

FEMA's planning guidance recommends that local governments identify and publicize shelter locations, but many jurisdictions have not updated these designations since the Cold War. Do not count on this infrastructure existing. Do your own survey.

Information Access When Networks Are Down

After a nuclear event, internet and cellular infrastructure may be destroyed, overloaded, or intentionally shut down. Your ability to access reference information — radiation dose charts, medical treatment protocols, water purification methods, fallout decay tables — depends entirely on what you have stored locally.

The Deadnet USB drive was designed for exactly this scenario. It contains 19 military and government source documents, including field medical references and survival manuals, along with a local AI assistant that runs without any internet connection. If you are sheltering for 48-72 hours and need to look up decontamination procedures or treatment for radiation burns, you need that information already on a device in your kit.

Print backups also work. The key documents to have in hard copy: FEMA's Nuclear Detonation Response Guidance, the CDC's radiation emergency quick reference, and a local area map with marked shelter locations and evacuation routes.

After Sheltering: The First 72 Hours

When authorities indicate it is safe to begin moving — or if you have instrumentation showing radiation levels below 0.5 R/hr — the next phase begins.

• Follow official evacuation routes. Fallout is not evenly distributed. Wind patterns create hot spots and clean corridors. Moving in the wrong direction can increase your exposure dramatically.
• Continue to avoid inhaling dust. Wear an N95 or cover your mouth and nose with a damp cloth.
• Do not eat or drink anything from outside that was not sealed before the event. Produce, open water sources, and livestock are all potentially contaminated.
• If you develop nausea, vomiting, or diarrhea within hours of exposure, seek medical attention. These are symptoms of acute radiation syndrome and the timeline of onset helps medical professionals estimate your dose.

What to Do This Week

Do not wait for a crisis to start planning. Pick one action from this list and complete it before the end of the week:

• Buy a 72-hour water supply (12 gallons for a family of four) and store it in your designated shelter area.
• Purchase a pack of KI tablets and a hand-crank AM/FM radio. Both are available for under $30 total.
• Walk through your home, workplace, and commute route. Identify the best shelter option at each location and note it.
• Load survival reference documents onto a USB drive or external hard drive. The Deadnet drive comes preloaded with military and government manuals and an offline AI, but at minimum, download FEMA's free nuclear detonation response PDFs and store them on a device you keep in your kit.

The 7/10 rule, 10 minutes of decisive action, and 72 hours of supplies. That is the framework. Everything else is refinement.