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

Most people assume a nuclear attack means instant death. That assumption kills more people than the blast itself. According to FEMA's Nuclear Detonation Response Guidance, basic preparedness knowledge and a few minutes of correct decision-making could save tens of thousands of lives in a single urban detonation event. The blast zone is lethal. Everything outside it is survivable — if you know what to do and when to do it.

This guide covers the three phases: what to prepare before an event, what to do in the minutes and hours during one, and how to survive the days and weeks after.

The Timeline You Are Working With

Understanding nuclear detonation timelines changes everything about how you prepare. FEMA's planning guidance identifies these windows:

• Warning time for a nuclear-armed ballistic missile: 15 to 30 minutes between alert and detonation
• Time to reach adequate shelter before fallout arrives: 10 minutes or more after detonation
• Peak fallout radiation intensity: first 1 to 2 hours
• Minimum recommended shelter-in-place duration: 24 hours
• Possible extended shelter duration: up to 1 month depending on yield, proximity, and wind patterns

Those numbers define your entire preparedness plan. You are not preparing for a single moment. You are preparing for a 24-hour sprint followed by a weeks-long grind.

Shelter: The Single Highest-Impact Preparation

The CDC's radiation emergency guidelines reduce nuclear survival to three principles: time, distance, and shielding. Of these, shielding — getting inside the right structure — offers the greatest protection for the lowest effort.

What Counts as Adequate Shelter

Not all buildings are equal. FEMA rates shelter quality by a Protection Factor (PF), which measures how much a structure reduces radiation exposure:

• Basement of a large concrete or brick building: PF 200+ (radiation reduced to less than 0.5% of outdoor levels)
• Center of a mid-rise concrete building (3+ stories): PF 100+
• Residential basement: PF 10-20
• Single-story wood-frame house: PF 2-3 (nearly useless)

A concrete basement cuts your radiation dose by 99.5%. A wood-frame house cuts it by roughly 50%. The difference between those two choices, made in under 10 minutes, is the difference between survivable exposure and acute radiation sickness.

Identify Your Shelters Now

Walk your daily routes — home, work, commute. For each location, identify the nearest structure with thick walls and a basement or below-grade parking. Underground parking garages, subway stations, and commercial building basements all qualify. You need to know where these are before an event, because you will not have time to search.

If your home lacks a basement, identify an interior room on the lowest floor with no exterior walls. Stack dense materials — books, soil-filled containers, water jugs — against exterior walls. Water is an effective radiation shield at roughly 18 cm (7 inches) of thickness for meaningful attenuation.

Supply Kit: 72 Hours Minimum, 30 Days Preferred

FEMA's 72-hour nuclear detonation response guidance establishes three days as the minimum shelter-in-place period, but radiation conditions may require up to a month indoors. Plan for both.

Water

• 1 gallon per person per day (the Red Cross standard)
• 72-hour minimum: 3 gallons per person
• 30-day target: 30 gallons per person
• Store in sealed, opaque containers away from direct sunlight
• Include water purification tablets or a gravity filter for resupply from compromised sources

Food

• Canned goods, freeze-dried meals, energy bars — anything that requires no refrigeration and minimal water to prepare
• 2,000 calories per person per day minimum
• Rotate stock every 6 to 12 months
• Manual can opener (this gets forgotten constantly)

Medical and Decontamination

• Potassium iodide (KI) tablets: the FDA recommends 130 mg for adults within 24 hours of exposure to radioactive iodine. KI protects the thyroid gland specifically — it does not protect against whole-body radiation
• Standard first aid kit with trauma supplies
• Plastic sheeting and duct tape for sealing windows and doors
• Large trash bags for contaminated clothing removal
• Baby shampoo or mild soap for decontamination washing

Information and Communication

• Battery-powered or hand-crank NOAA weather radio (this is your primary information source when cell networks fail)
• Spare batteries
• Copies of emergency plans, contact numbers, and medical records on paper
• A USB drive loaded with offline reference materials — including military field manuals covering nuclear, biological, and chemical survival. The Deadnet USB includes the Army's FM 3-11 CBRN manual and 18 other government source documents accessible without any internet connection, which matters when communications infrastructure is down.

During a Detonation: The First 10 Minutes

If you see a bright flash or receive an emergency alert:

1. Do not look at the fireball. It causes temporary or permanent blindness at distances well beyond the lethal blast radius.
2. If outdoors, get behind any solid structure immediately. Drop flat and cover exposed skin if no structure is within a few seconds' reach.
3. After the blast wave passes (seconds to a minute depending on distance), move to the best available shelter within 10 minutes.
4. Go to the basement or the center of the building. Every wall and floor between you and the outside reduces exposure.
5. Remove outer clothing before entering shelter. The CDC states that removing your outer layer eliminates up to 90% of radioactive material on your body.
6. Seal the room if possible. Close windows, shut off HVAC systems, and seal gaps with plastic sheeting and tape.

The instinct to flee will be strong. Resist it. FEMA's planning guidance is unambiguous: sheltering in place for the first 24 hours saves more lives than evacuation in nearly all scenarios. Evacuating through fallout zones causes more radiation exposure than staying in a mediocre shelter.

The First 24 Hours: Shelter-in-Place Protocol

Once inside adequate shelter, your priorities shift to information gathering and exposure management.

Monitor Radiation Levels

If you have a dosimeter or radiation detection device, monitor ambient levels. If you do not (most people won't), follow the 24-hour rule: do not leave shelter for at least 24 hours unless the structure is compromised or you receive official guidance to evacuate.

Fallout radiation intensity decreases following the 7-10 rule: for every sevenfold increase in time after detonation, radiation drops by a factor of 10. At 7 hours post-detonation, radiation is 10% of its 1-hour level. At 49 hours (roughly 2 days), it drops to 1%. This decay curve is why the first 24 hours of sheltering have such outsized impact.

Ration Water and Food

Assume no resupply for 72 hours. Strict rationing from hour one prevents a crisis at hour 48. Adults can function on half a gallon of water per day in sedentary conditions, though 1 gallon remains the recommended target.

Manage Human Waste

This is the preparation gap most people ignore. A 5-gallon bucket with heavy-duty trash bags and a supply of kitty litter or lime creates a functional latrine for a small group for days. Without it, sanitation degrades fast, and in a sealed shelter, that becomes a health hazard within hours.

Days 2 Through 30: Extended Survival

After the first 24 to 48 hours, radiation levels drop enough that brief outdoor exposure becomes manageable — but "manageable" requires discipline.

Limit Exposure Time

Any trip outside should be planned, timed, and minimized. Use the principle of ALARA — As Low As Reasonably Achievable. Exposure is cumulative. Ten 5-minute trips cause less damage than one 50-minute trip if you return to shelter between them, allowing your body some recovery time.

Water Resupply

Groundwater and sealed municipal water systems are generally safer than surface water after fallout. If collecting rainwater or surface water, let particulates settle, filter through cloth, then purify. Fallout particles are relatively large and can be filtered mechanically. Dissolved radioactive isotopes cannot be removed by basic filtration — activated carbon and ion exchange filters offer partial reduction.

Food Safety

Canned and sealed packaged food is safe regardless of external contamination. Wash the exterior of containers before opening. Food that was exposed to fallout outdoors should be washed thoroughly. Root vegetables in the ground are safer than leafy greens that were exposed to direct fallout deposition.

The USDA and FDA have standing guidance on food safety after radiological events — having these references available offline is the difference between guessing and knowing. The Deadnet USB drive carries these federal source documents in a format readable without power grid or internet access, using a local AI assistant that runs entirely on your device.

Communications and Information

After a nuclear event, expect the following communication failures:

• Cell networks: overwhelmed within minutes, likely nonfunctional for days to weeks
• Internet: infrastructure damage and power loss take it offline across a wide area
• Broadcast TV: some stations may survive with backup power, but reception depends on your equipment
• AM/FM radio: highest likelihood of continued operation, especially AM stations with backup generators
• NOAA Weather Radio: maintained by the National Weather Service with backup power systems, broadcasts emergency information on dedicated frequencies (162.400 to 162.550 MHz)

A hand-crank radio is the most reliable information tool in this scenario. Battery-powered radios work but depend on your battery supply. Know your local NOAA frequencies before an event.

If you have a ham radio license and equipment, the amateur radio emergency network (ARES) provides communications when all commercial infrastructure fails. Even without a license, FCC regulations permit unlicensed transmission in life-threatening emergencies on any frequency.

Decontamination Procedures

If you or anyone in your group has been exposed to outdoor air or fallout:

1. Remove all outer clothing and shoes. Bag them in plastic and leave them outside the shelter area.
2. Shower or wash with warm water and soap. Do not scrub hard — abrasion opens the skin to contamination. Do not use conditioner, as it binds radioactive particles to hair.
3. Blow your nose, wipe eyelids and ears with a damp cloth.
4. If water is limited, use wet wipes or a damp cloth on all exposed skin, working from head to feet.
5. Put on clean clothing from inside the shelter.

The CDC confirms that removing outer clothing alone eliminates up to 90% of external contamination. A basic wash removes most of the remainder.

Psychological Preparedness

Columbia University's National Center for Disaster Preparedness identifies psychological readiness as a measurable factor in survival outcomes. People who have mentally rehearsed emergency scenarios respond faster and make fewer errors under stress.

Walk through your plan quarterly. Know the route to your shelter. Know where your supplies are. Know what the first 10 minutes look like. Mental rehearsal costs nothing and directly reduces the freeze response that kills people who otherwise had every physical advantage.

Expect fear, grief, and disorientation in yourself and others. These are normal physiological responses, not weaknesses. Having a structured plan to follow — even a simple checklist on paper — reduces cognitive load when your brain is operating under extreme stress.

Your Next Step

Today — not this weekend, not next month — identify the best shelter location within 10 minutes of where you are right now. Then do the same for your workplace and any other location where you spend significant time. Write these locations down on a card and keep it in your wallet. That single action, completed in 20 minutes, addresses the highest-impact variable in nuclear survival: whether you reach adequate shelter before fallout arrives. Everything else in this guide builds on that foundation.