Threat Model, Honestly
Flash
Light and heat arrive immediately. If you see a flash, do not look at it; drop behind cover and protect skin.
Blast
The shock wave arrives after the flash. At damaging distances it can still be tens of seconds later; cover cuts glass and debris injuries.
Fallout
Radioactive particles from ground or near-ground bursts can arrive minutes to hours later. This is the hazard sheltering can beat.
EMP
Electronics and grid damage are possible. The survival response is still analog: shelter, battery radio, printed instructions.
| Scenario | What changes | First 48 hours | Gotcha |
|---|---|---|---|
| Improvised or terrorist device | Likely one city or port; local fallout depends on burst height and wind. | Same: get inside, center/basement, stay tuned, avoid self-evacuation through fallout. | Traffic panic can put you outside during the highest dose period. |
| Single regional strike | Blast/fire zone is local; fallout plume can cross counties or states. | Same first-hour protocol; follow local evacuation only after plume route is understood. | Being outside the visible damage zone does not mean outside the fallout zone. |
| Limited exchange | Communications and supply chains degrade; more uncertainty after the first day. | Shelter-first still dominates dose reduction. Conserve water, batteries, sanitation capacity. | Early radio silence is not an all-clear. |
| Large exchange | National recovery is harder; multiple fallout periods may occur. | The first two weeks still matter. Most of the initial fallout dose rate decays rapidly. | Fatalism kills useful action; local dose and shelter quality decide many outcomes. |
Five deadly myths
- "If you see the flash, you are dead." Wrong. Seeing the flash can be the warning that lets you drop before blast and get inside before fallout.
- "Fallout poisons all air." Fallout is particulate. Keep dust out, but do not make an occupied shelter airtight.
- "Radiation lasts for centuries everywhere." Fallout dose rate decays fast at first; contamination sites are a different problem.
- "Nuclear winter makes shelter pointless." Climate debate does not change the first-hour and two-week survival problem.
- "Gear matters more than mass." A basement corner with heavy shielding can beat expensive equipment in a bad location.
The useful mental model
Dose = dose rate x time / protection factor. You can improve all three variables: wait while dose rate falls, reduce outside trips, and put heavy material between you and fallout.
The page uses US public-health sources for current medical/alert guidance, but it avoids tactical weapons detail beyond what affects shelter decisions.
Quick Reference: The First Hour
| Downwind distance | Very rough arrival window | Action | Gotcha |
|---|---|---|---|
| 2 mi | Minutes if local surface fallout is produced | Use the nearest substantial shelter; do not drive. | Blast/fire injuries may dominate this close. |
| 5 mi | About 10-30 min | Basement or center core now; improve after entry. | Waiting to gather gear can cost more dose than the gear saves. |
| 10 mi | About 15-60 min | Move heavy material to shelter side facing roof/outside walls. | Wind, rain, and burst height matter more than distance alone. |
| 20 mi | About 30 min to 2 hr | Fill containers, shut obvious dust paths, keep radio on. | Visible cloud direction may not match ground winds. |
| 50 mi | Hours | Prepare for sheltering before any dust arrives. | Rainout can create localized hot spots far away. |
| 100+ mi | Several hours to a day | Follow official plume instructions; keep inside ready. | No visible fallout does not prove no measurable dose. |
Verified Ready.gov states that after a detonation people generally have 10 minutes or more to find adequate shelter before fallout arrives; Kearny gives the same operational lesson from older attack-warning analysis.
The 7-10 Rule and Two-Week Clock
Rule
Every 7-fold increase in time after detonation cuts fallout dose rate by about 10-fold.
This is a planning rule, not a meter reading. Real fallout varies by particle mix, weathering, and local deposition.
| Time after detonation | Reference dose rate | Operational meaning |
|---|---|---|
| H+1 hr | 1000 R/hr | Heavy-fallout reference point from Kearny; survival depends on being shielded. |
| H+7 hr | 100 R/hr | Still dangerous outside; urgent tasks only if life-critical and timed. |
| H+49 hr | 10 R/hr | Short trips may be possible with a meter and high PF shelter, but day 2 is not an all-clear. |
| H+96 hr | ~4 R/hr | Many decisions shift from absolute sheltering to measured, limited outside work. |
| H+14 days | ~1 R/hr | Kearny: most shelter occupants could stop continuous sheltering or work outside increasing hours if local readings allow. |
Dose bands for context
| Whole-body acute dose | Likely effects | Decision implication |
|---|---|---|
| <0.3 Gy | No ARS expected for most people; still minimize avoidable dose. | Useful planning ceiling for non-urgent tasks, not a target. |
| 0.3-0.7 Gy | CDC: mild symptoms may occur as low as 0.3 Gy; classical ARS threshold is higher. | Track cumulative dose; do not spend it on curiosity. |
| 0.7-1.5 Gy | CDC: bone marrow syndrome can begin above 0.7 Gy; nausea/vomiting possible. | Requires medical awareness if care exists; preserve rest and sanitation. |
| 1.5-3 Gy | Increasing hematopoietic injury; infection and bleeding risk rise. | Every avoidable outside minute matters. |
| 3-5 Gy | CDC lists LD50/60 around 2.5-5 Gy without comparable modern care. | High mortality in disrupted conditions; shelter and triage dominate. |
| 5-8 Gy | Severe ARS; REMM/NATO tables show vomiting, diarrhea, bleeding/infection risks. | Do not attempt rescue tasks that trade one life for multiple lethal doses. |
| >10 Gy | CDC: GI syndrome usually occurs above about 10 Gy; survival extremely unlikely. | Indicates catastrophic exposure or inadequate shelter. |
| >20-50 Gy | CDC: CV/CNS syndrome can appear; death can occur within days. | Outside meaningful self-help range. |
For fallout gamma, old civil-defense roentgen estimates and modern whole-body gray bands are close enough for field planning at this level: 100 R is roughly 1 Gy for penetrating gamma exposure, but medical dosimetry is more nuanced.
Protection Factor Math
Formula
PF = outside dose / inside dose
Example: if outside is 31 R/hr and your shelter is 0.2 R/hr, then PF 155. Kearny uses this exact style of measurement example for finding shelter PF.
Gamma halving thickness, visualized
Approximate thickness that halves gamma exposure. Stacking halving-thicknesses multiplies: 5 halvings is 1/32, 10 halvings is 1/1024.
Concrete and packed-earth values are from Kearny/NWSS. Household material values are rounded field-planning approximations: density is what matters.
| Location | Typical PF target | Use when | When not to use |
|---|---|---|---|
| Car | ~1-2 | Only as a bridge to a real building. | Do not flee in a plume; glass, thin metal, and traffic make it poor shelter. |
| Light frame house | ~2-3 | Better than outside if it is the only immediate option. | Do not stay upstairs near roof and exterior walls if a basement exists. |
| Brick/concrete building interior | ~5-20 | Good urban default; move to center floors or basement. | A glass lobby is not the building's protective core. |
| Ordinary basement | ~10-20 | Best common home starting point. | Weak if directly under exposed roof or beside above-grade window wells. |
| Basement corner plus mass | PF 40+ | Use tables, doors, books, water, earth-filled drawers, and dense storage. | Do not collapse supports or block all air paths. |
| Subway/deep interior | PF 100+ | Excellent if reachable before fallout and allowed by officials. | Do not cross open fallout to reach it after deposition starts. |
| Kearny earth trench | PF 200+ | Rural or pre-crisis warning with tools, earth, water, and ventilation. | Urban apartment dwellers should improve building shelter instead. |
Worked example: basement PF-40 corner
- Pick geometry: choose the basement corner farthest from exterior walls, roof, and exposed windows. Corners under earth-grade walls usually win.
- Build overhead mass: lay a sturdy interior door or table over the sleeping area. Load it only if the supports can safely carry the weight.
- Add side mass: stack book boxes, filled water containers, tool chests, canned food, and earth-filled drawers around two exposed sides. Twelve inches of books/paper or water is roughly 1.5 halving-thicknesses; 24 inches is roughly 3.
- Block line of sight: gamma scatters, but direct sky/ground paths through windows and stairs are bad. Turn the entry path or stack mass near it while preserving airflow.
- Keep air: do not tape yourself into a sealed room. Use cloth or filters to reduce dust entry, not to suffocate.
- Estimate: ordinary basement PF 10-20 plus several halving-thicknesses of dense improvised mass can plausibly reach PF 40+ in the best corner. Verify with a meter if available.
Example final answer: outside 100 R/hr at H+7 and shelter PF 40 means inside dose rate about 2.5 R/hr. Six hours inside adds about 15 R, not 600 R.
Expedient Shelters: Kearny Designs
Kearny App. A.1: PF 250; practical where at least one hollow-core door per occupant is available and stable earth can be dug. Typical family: hard work for most of 36 hours; stronger families completed in under 24 hours.
Kearny's Tennessee and Utah family trials showed untrained families could complete earth-covered trench shelters within two days in simulated crisis conditions, using hand tools and local materials.
Kearny App. A.4: minimum illustrated length shelters four people with six doors; useful where a water table or rock prevents a deep trench. It still needs earth or earth-filled rolls for shielding.
Kearny Air Pump
Kearny warns that crowded high-PF shelters can become dangerously hot and humid. His KAP instructions target about 40 cfm/person in hot humid weather; the 36 x 29 in model can pump about 1000 cfm with proper openings.
Do not: seal a shelter airtight. Fallout dust is a problem; suffocation, heat, carbon dioxide, and humidity can be faster problems.
Water beside shelter
Kearny's expedient shelter instructions call for storing 15 gal/person in or near the shelter. That roughly matches a two-week survival minimum, not comfort.
Gotcha: water is also shielding. Put containers where they add mass between occupants and fallout, but do not create a leak/flood hazard.
The Kearny Fallout Meter
What it is
The KFM is a homemade electroscope dose-rate meter built from common materials such as a can, foil leaves, thread, plastic, tape, and a drying agent. Kearny says average untrained families could build one in 3-4 hr and learn to use it in about 1.5 hr.
It measures gamma dose rate by timing the discharge of charged foil leaves. Kearny's instructions include tables for converting leaf movement into R/hr.
Critical limit: digital printouts or photocopies of the templates may not be scale-accurate. If you plan to rely on one, build and test it before a crisis.
Modern alternatives
- GM counter: useful for contamination and low-level checks; many cheap units saturate or under-read at high fallout dose rates.
- Ion chamber / survey meter: better for high dose rates if calibrated and powered.
- Chirper alarm: useful as a wake-up warning, not a replacement for dose planning.
- No meter: use the 7-10 rule, official instructions, and conservative shelter timing.
Life Support for 14 Days
| Need | Minimum planning number | Concrete setup | Gotcha |
|---|---|---|---|
| Water | 1 gal/person/day; Kearny shelter target 15 gal/person | Fill tubs, pots, water heater access, sealed jugs, lined bins near shelter. | Boiling kills organisms but does not remove radioactive material; settling/earth filtering removes particles, then disinfect. |
| Food | Two weeks shelf-stable food | Cans, rice, oats, beans, peanut butter, ready-to-eat food for first days. | Fallout does not penetrate sealed cans; wipe containers before opening. |
| Sanitation | One lined 5-gal bucket, lid, bags, absorbent per family minimum | Bucket near exhaust side; separate urine if practical; tie waste bags; keep fly/odor control. | Kearny emphasizes sanitation as health and morale critical. Rotting waste produces gas; do not seal rigid containers without venting. |
| Ventilation | 3 cfm/person cold-weather minimum; up to 40 cfm/person hot weather | Preserve two air paths if possible; use cloth to reduce dust; fan manually if hot. | Airtight sheltering is a common lethal mistake. |
| Potassium iodide | Age-based single dose only when officials advise | Store FDA-approved KI if in planning kit; know child doses before stress. | KI protects thyroid from radioactive iodine only. It is not a whole-body radiation cure. |
| Meds | At least 14 days of daily prescriptions if possible | Keep in an interior go-bag with glasses, hearing-aid batteries, wound supplies. | Do not stop critical medication because the bottle was outside; CDC says wipe outside containers. |
| Light/heat | Battery lights preferred | Headlamps, lanterns, spare batteries, glow sticks. | Candles consume oxygen and create fire/CO risk; use sparingly with ventilation. |
| Morale | Quiet routine | Cards, notebook, printed instructions, sleep rotation, privacy sheet. | Panic-driven outside trips are dose multipliers. |
KI dosing, current CDC/FDA table as of Jan 2025
| Group | Predicted thyroid exposure threshold | Single dose | Do not miss |
|---|---|---|---|
| Infants birth through 1 month | >=5 cGy | 16 mg | Use oral solution if available; medical follow-up if more than one dose. |
| Children 1 month through 3 years | >=5 cGy | 32 mg | Half of a 65 mg tablet only if directed and prepared correctly. |
| Children over 3 through 12 years | >=5 cGy | 65 mg | One 65 mg tablet or half 130 mg tablet. |
| Adolescents 12 through 18 years | >=5 cGy | 65 mg; 130 mg if >150 lb | Adult-sized adolescents receive adult dose. |
| Adults over 18 through 40 | >=10 cGy | 130 mg | One dose protects about 24 hours; repeat only if officials advise. |
| Pregnant or lactating women | >=5 cGy | 130 mg | CDC/REMM: breastfeeding may need temporary interruption if alternatives exist. |
| Adults over 40 | >=500 cGy | 130 mg | Use only when officials say exposure is high enough; side-effect risk is higher relative to thyroid-cancer benefit. |
Communications and Modern Updates
WEA/IPAWS
FEMA IPAWS feeds Wireless Emergency Alerts, EAS radio/TV, and NOAA Weather Radio. Keep phone alerts enabled, but assume networks may be degraded.
NOAA radio
NOAA Weather Radio All Hazards broadcasts official warnings and post-event information. Store batteries and know your local channel.
AM/FM
AM broadcast is robust and easy to receive. Battery radios with local station presets are worth more than internet-only plans.
Handheld radio
Use for listening and licensed amateur/GMRS operations. Do not transmit illegally unless life safety clearly requires emergency use.
Kearny said
FEMA/CDC now say
Related preparedness and radio sheets
Emergency Radio Card | Baofeng UV-5R Quick Reference | Baofeng Ham Setup Guide | Ham Radio Technician
Common Mistakes
Fleeing by car
Driving during fallout arrival trades a low-PF vehicle and traffic gridlock for the highest dose-rate period. Shelter first unless officials give a route and timing.
Sheltering upstairs
Comfort upstairs can mean roof and exterior-wall exposure. Move to basement or center core, then improve comfort.
Leaving on day 2
H+49 hours is much safer than H+1, but not automatically safe. Use meter readings or official instructions.
Taking KI like a cure
KI is thyroid-only and timing-specific. It does nothing for external fallout gamma dose.
Sealing airtight
Dust control is good. Carbon dioxide, heat, humidity, candle fumes, and sanitation gases can become immediate hazards.
One fragile water store
A single bathtub liner or jug stack can fail. Spread water across multiple containers and shielded locations.
Buying before reading
Two hours with Kearny, FEMA, CDC, and your basement layout beats another gadget you do not know how to use.
Ignoring sanitation
A bucket, bags, lid, absorbent, gloves, bleach, and privacy sheet prevent disease and panic in ways no meter can.
Printable Fallout Shelter Card
First hour
Improve PF
14 days
Sources and Verification
Primary and official sources used:
- Cresson H. Kearny, Nuclear War Survival Skills, 1987 edition - public-domain ORNL original plus Kearny additions; decay, shelters, KAP, KFM, water/sanitation.
- FEMA, Planning Guidance for Response to a Nuclear Detonation, 3rd ed. (2022) - current US response doctrine.
- Ready.gov Radiation Emergencies and CDC Radiation Emergencies - get inside/stay inside/stay tuned, food/water safety.
- CDC Potassium Iodide, FDA KI FAQ, and REMM KI guidance - KI dosing and limits.
- CDC Acute Radiation Syndrome and REMM time/dose effects - dose-effect bands.
- FEMA IPAWS and NOAA Weather Radio - modern alerting channels.
Freshness policy: decay physics and Kearny trial data are stable; FEMA/CDC/FDA/REMM guidance, alert-system names, and KI dosing should be rechecked yearly or after major agency updates.