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

The Bulletin of the Atomic Scientists set the Doomsday Clock to 85 seconds to midnight in January 2026 — the closest it has ever been. The New START treaty, the last bilateral agreement limiting U.S. and Russian nuclear arsenals, expired on February 5, 2026. No replacement is in place. The WHO has begun preparing for nuclear scenarios tied to escalating tensions in the Middle East.

None of this means a nuclear event is imminent. It means the conditions that make one possible are deteriorating faster than at any point since the Cold War. This guide covers what federal agencies actually recommend, what the physics of a detonation demand from you, and how to prepare now rather than after a warning.

Understanding the Threat Spectrum

Not all nuclear events are the same, and your response plan changes depending on what happens. The three scenarios worth preparing for:

• A nuclear detonation in or near a populated area (the worst case)
• A radiological dispersal device, commonly called a dirty bomb, which spreads radioactive material without a nuclear explosion
• A nuclear facility accident, similar to Fukushima or Chernobyl

According to FEMA's Planning Guidance for Response to a Nuclear Detonation, even a single low-yield weapon (under 10 kilotons) detonated at ground level in an urban area could produce casualties in the tens of thousands — but the majority of deaths beyond the immediate blast zone would come from people failing to shelter properly in the first hours.

That last point matters. The physics of fallout mean that what you do in the first 10 to 60 minutes determines your survival odds more than almost any other factor.

The 10-Minute Rule

After a nuclear detonation, FEMA estimates you have approximately 10 minutes or more before radioactive fallout begins arriving at ground level, depending on your distance from the blast. This is your window.

In that window, you need to get inside the nearest substantial structure. Not a car. Not a mobile home. A building with thick walls and, ideally, a basement.

FEMA's shelter-in-place guidance for nuclear events ranks buildings by a Protection Factor (PF):

• A basement in a large concrete or brick building: PF of 200 or higher (reduces radiation exposure by 200x)
• A middle floor of a high-rise: PF of 100 or higher
• A residential basement: PF of 10 to 20
• A single-story wood-frame house with no basement: PF of 2 to 3

A PF of 10 means you receive one-tenth the radiation dose you would get standing outside. The difference between sheltering in a residential basement (PF 10-20) and being in your car (PF under 2) is the difference between a survivable and a lethal dose.

If you are outdoors and cannot reach a substantial building within a few minutes, any shelter is better than none. Get inside, move to interior rooms, away from windows and exterior walls. Then stay there.

The First 24 Hours

FEMA's nuclear detonation response guidance directs survivors to remain in the most protective location available for at least the first 24 hours unless an immediate hazard (structural collapse, fire) forces you to move.

Here is why: radioactive fallout decays rapidly following what physicists call the 7-10 rule. For every sevenfold increase in time after the detonation, radiation intensity drops by a factor of 10.

• 1 hour after detonation: radiation at 100% intensity
• 7 hours after: radiation drops to 10% of initial levels
• 49 hours (roughly 2 days) after: radiation drops to 1% of initial levels
• 2 weeks after: radiation drops to 0.1% of initial levels

This decay curve is why the first 24 hours of sheltering matter so much. You are waiting out the most dangerous period. Leaving shelter early — even for a few minutes — during the first hours can expose you to radiation doses that would otherwise have decayed to manageable levels had you waited.

What to Have Ready Before It Happens

You cannot buy supplies after a nuclear event. Stores will be closed, roads impassable, supply chains stopped. The following list is based on Ready.gov recommendations and FEMA's nuclear preparedness materials.

Water

• One gallon per person per day for a minimum of 14 days (FEMA recommends two weeks of shelter readiness for nuclear events)
• For a family of four, that is 56 gallons — roughly three standard 20-gallon water containers
• Water purification tablets or a gravity-fed filter as a backup
• Sealed containers stored away from direct sunlight

Food

• 14-day supply of non-perishable food per person
• Prioritize calorie density: peanut butter (190 calories per serving), canned meats, rice, dried beans, energy bars
• Manual can opener (not electric)
• No foods requiring refrigeration or significant water to prepare

Radiation-Specific Supplies

• Potassium iodide (KI) tablets: the FDA recommends KI to protect the thyroid gland from radioactive iodine. Dosage for adults is 130mg. These must be taken within hours of exposure to be effective — not days later. They do not protect against other radioactive isotopes.
• N95 masks or better: fallout particles are physical debris. A mask reduces inhalation risk during any necessary movement.
• Plastic sheeting and duct tape: for sealing windows and doors in your shelter room to reduce particulate infiltration.
• A change of clothes stored in a sealed bag: if you are exposed to fallout, removing and bagging your outer clothing removes approximately 90% of radioactive material on your body, according to Ready.gov.

Communication and Information

• Battery-powered or hand-crank AM/FM radio: this is your primary link to emergency broadcasts. NOAA Weather Radio frequencies (162.400 to 162.550 MHz) carry Emergency Alert System messages.
• Extra batteries, stored separately from devices
• A written list of emergency contacts, local shelter locations, and rally points for your household. Phones may not work. Cell towers may be down or overloaded.

Medical

• 30-day supply of any prescription medications
• Standard first aid kit with trauma supplies (tourniquet, hemostatic gauze, chest seals)
• Oral rehydration salts
• Anti-diarrheal and anti-nausea medications

Building Your Shelter Plan

Having supplies means nothing without a plan for where to go. Identify three locations in advance:

1. Your primary shelter: ideally your home, if it has a basement. Know which room offers the most mass between you and the outside (interior rooms, below grade).

2. A secondary shelter within 10 minutes of your workplace or school. This is the building you move to if an event happens during the day. Scout this now. Look for large concrete structures, parking garages with underground levels, commercial basements.

3. A rally point for your household. If family members are in different locations, where do they shelter first, and where do they reunite when authorities give the all-clear? Write this down. Everyone in your household should know the plan without needing a phone to check.

FEMA's shelter guidance emphasizes that adequate shelter is already all around most people. You are not building a bunker. You are identifying the best existing structures near the places you already spend time.

Fallout and Decontamination

If you were outdoors during fallout or had to move between buildings, decontamination is straightforward:

1. Remove all outer clothing before entering your shelter. Place it in a plastic bag and leave it outside the shelter area. This single step removes roughly 90% of external contamination.
2. Shower or wash with soap and water. Do not scrub hard — you are washing particles off, not decontaminating your skin. Scrubbing can cause micro-abrasions that allow particles to enter.
3. Shampoo your hair but do not use conditioner. Conditioner binds particles to hair.
4. Blow your nose, wipe your eyelids and ears with a damp cloth.
5. Put on the clean clothes from your sealed bag.

If water for showering is not available, wipe exposed skin with damp cloths, working from head to feet, and change clothes.

What About Iodine, Gas Masks, and Fallout Shelters

A few common questions addressed directly:

Potassium iodide is not a general anti-radiation drug. It blocks the thyroid from absorbing radioactive iodine-131, one specific isotope released in nuclear events. It does nothing against external gamma radiation or other isotopes. Take it only when directed by authorities, and within the recommended window (ideally within 3-4 hours of exposure).

Gas masks with CBRN-rated filters provide protection during movement through contaminated areas, but they are not a substitute for shelter. An N95 mask covers the most likely inhalation risk (particulate fallout) at a fraction of the cost and complexity.

The United States decommissioned its public fallout shelter program decades ago. The yellow and black shelter signs you occasionally see on older buildings are historical artifacts. Those buildings may or may not still offer adequate protection — their value is in their construction (concrete, mass), not the sign.

The Information Problem

After a nuclear event, your ability to access accurate information determines the quality of every decision you make. What direction is fallout moving? When is it safe to leave shelter? Where are evacuation corridors?

If cell towers are down, internet is unavailable, and broadcast infrastructure is damaged, you are operating on whatever information you stored beforehand.

This is where having offline reference material becomes a practical advantage rather than a theoretical one. The Deadnet USB drive includes the full text of FEMA's Nuclear Detonation Planning Guidance along with 18 other military and government source documents — field manuals covering first aid, water purification, shelter construction, and navigation. It also runs a local AI assistant that works without any internet connection, so you can query those documents in plain language when you need specific answers fast. At $79, it is a compact backup for the exact scenario where your phone becomes a paperweight.

Regardless of what tool you use, the principle holds: download or store critical reference documents now. FEMA's nuclear detonation response guidance, the Ready.gov nuclear preparedness pages, and local emergency plans are all available as PDFs. Put them on a USB drive, print the most critical pages, or both.

Psychological Preparedness

Columbia University's National Center for Disaster Preparedness notes that psychological response to nuclear events follows predictable patterns: initial shock, followed by information-seeking behavior, followed by either purposeful action or panic — depending largely on whether the individual has a pre-existing plan.

Having a plan does not just improve your physical outcomes. It shortens the gap between the event and purposeful action. People who have rehearsed their response — even mentally — move faster and make fewer errors under stress.

Walk through the scenario with your household:

• Where do you shelter?
• What do you grab in the first 5 minutes?
• How do you communicate if phones are down?
• Who picks up the kids and where do they go?
• What does the first 24 hours look like inside your shelter?

You do not need to make this dramatic. A 15-minute conversation over dinner and a written one-page plan covers it.

Your Next Step

Today — not this week, not when things get worse — identify the best shelter location within 10 minutes of where you are right now. Look for basements, underground parking structures, or interior rooms in large concrete buildings. Write down the address. Then check whether you have at least 3 days of water stored at home (one gallon per person per day). If not, fill three containers and put them in your basement or a closet. That single action puts you ahead of the majority of the population, which according to FEMA surveys, has not taken any specific steps to prepare for a nuclear or radiological event.