Kaboomly / Fallout
Nuclear Fallout Map
Fallout is the part of a nuclear explosion that the wind carries away. It can land far from the blast, and where it lands depends on the weather at that moment. This page explains how it forms and how our map draws an idealized version of it for a surface burst.
Fallout is shown as an idealized illustration, for surface bursts only. The map above draws the downwind pattern from Glasstone and Dolan's own Table 9.93, using one fixed 15 mph wind that never changes direction. It is not a weather forecast, and it never shows death or injury numbers, only distances. Airbursts show no fallout pattern at all.
What fallout is
A nuclear explosion creates radioactive fission products. In the fireball they are vaporized along with the weapon materials and anything else drawn in. As the cloud rises and cools, these materials condense onto particles of many sizes. When the particles fall back to Earth, the radioactive material they carry is called fallout. Glasstone and Dolan cover the subject in chapter IX of The Effects of Nuclear Weapons (1977).
The book separates fallout by timing. Early fallout reaches the ground within about a day and is made of larger, heavier particles. It can deliver high radiation doses downwind of the explosion. Delayed fallout is made of very fine particles that stay in the upper atmosphere for months or years and settle over large parts of the world at much lower levels.
Why the burst type matters
How much early fallout there is depends mostly on whether the fireball touches the ground. In a surface burst, large amounts of soil and debris are pulled up into the fireball and the rising cloud. Radioactive material condenses onto these particles, and the heavier ones start to fall within minutes to hours. This produces heavy local fallout.
In an airburst where the fireball stays above the ground, there is little soil to carry the radioactive material down. It forms extremely small particles that rise high and spread thinly, so early fallout near the explosion is light. In the nuke simulator, the airburst option uses a fixed height at which the fireball stays clear of the ground for every preset weapon.
Why wind and weather decide the map
A fallout pattern is drawn by the wind. Particles fall from different heights of the cloud, and the wind at each height can blow in a different direction and at a different speed. Heavy particles land close to the explosion; lighter ones travel much farther before they reach the ground.
With a steady wind in one direction, the result is a long area stretched downwind. Real weather is rarely that tidy. Wind that turns with height can bend or widen the pattern, and rain can wash particles out of the air in some places and not others, leaving patches of higher contamination. Glasstone and Dolan stress that the idealized patterns in chapter IX are simplified and that actual patterns can be very irregular.
A well-known example is the Castle Bravo test at Bikini Atoll in 1954, which Glasstone and Dolan discuss in chapter IX. Its yield was far larger than expected, and fallout spread over inhabited atolls and a Japanese fishing boat outside the area that had been cleared. The episode is one reason fallout became a major subject of study.
How fallout changes over time
Fallout radioactivity is highest soon after it lands and then drops, quickly at first and more slowly later. Glasstone and Dolan give a rule of thumb in chapter IX: for every sevenfold increase in time after the explosion, the dose rate falls by a factor of about ten. The rule is an approximation. Real decay depends on the mix of materials in the fallout.
How this map draws fallout, and why it is idealized
Other simulators draw fallout with a simplified model usually credited to work by Carl F. Miller. Our standard is that every number on this site must trace back to a source we can cite in full: title, organization, year, and report number. We could not locate and verify the original Miller report, so instead of using it we use Glasstone and Dolan's own idealized fallout contours, Table 9.93 in chapter IX, which are fully cited (sources section of How It Works, and the fallout section above it explains the method in full).
That table describes an "idealized" pattern: a smooth, cigar-shaped area for one fixed effective wind of 15 miles per hour, not real weather for any place or day. For a surface burst of the chosen yield, the map shades four of the table's eight dose-rate contours (1,000, 100, 10, and 1 rad per hour, one hour after the explosion) downwind of ground zero, always toward the east. It never changes with the city, season, or real wind, and it is not a prediction for any real event. An airburst shows no fallout pattern at all, because Glasstone and Dolan state that its residues rise too high within about a minute to reach the ground in significant amounts (§9.04).
What the simulator shows
- Blast: the 20 psi, 5 psi, and 1 psi overpressure rings.
- Heat: the distance for a 50% chance of third-degree burns on bare skin.
- Initial radiation: the 500 rem dose from neutrons and gamma rays in the first minute. This is not fallout; it comes from the explosion itself.
- Fireball: its maximum size.
- Fallout (surface bursts only): the idealized downwind pattern described above, for one fixed 15 mph wind.
The nuclear blast radius page explains each ring with a table for every preset, and the nuclear bomb map guide covers how to explore the map.
Real-world information
This page is educational and is not safety guidance. For real-world preparedness information, see official sources such as Ready.gov in the United States, or your national or local emergency management agency.
Frequently asked questions
What is nuclear fallout?
Fallout is radioactive material that falls back to the ground after a nuclear explosion. It is mostly made of fission products that condense onto particles of soil, debris, and weapon material carried up into the mushroom cloud. Glasstone and Dolan describe it in chapter IX of The Effects of Nuclear Weapons (1977).
Does this nuclear fallout map show a fallout plume?
Yes, for a surface burst. The map draws an idealized downwind pattern from Glasstone and Dolan Table 9.93, a fixed textbook illustration for a 15 mph wind, not a real forecast. An airburst shows no fallout pattern, because Glasstone and Dolan state that its residues rise too high in the first minute to reach the ground in significant amounts (§9.04).
Why does fallout depend so much on the wind?
Fallout particles drift with the wind as they fall, and the wind usually blows in different directions and at different speeds at different heights. The same explosion can leave a long narrow pattern on one day and a shorter, wider or split pattern on another. Rain can also bring particles down unevenly.
Do airbursts produce fallout?
Much less locally. When the fireball does not touch the ground, the radioactive material forms very fine particles that rise high and spread widely before settling slowly, so there is little early fallout near the explosion. A surface burst draws large amounts of soil into the fireball, which produces heavier particles that fall nearby within hours.
How long does fallout stay dangerous?
Fallout radioactivity drops quickly at first and then more slowly. Glasstone and Dolan give an approximate rule in chapter IX: for every sevenfold increase in time after the explosion, the dose rate falls by a factor of about ten. It is an approximation, and real decay depends on the mix of materials.
Is the 500 rem ring on the map the same as fallout?
No. The 500 rem ring shows initial radiation, the neutrons and gamma rays released within the first minute. Fallout is residual radiation that arrives later, sometimes far away, and it is shown separately, as the idealized downwind pattern (surface bursts only).
Where can I find real emergency guidance about fallout?
This site is an educational tool, not a source of safety advice. For real-world preparedness information, use official sources such as Ready.gov in the United States or your national or local emergency management agency.