Trinity on Chicago
25 kt fission weapon · USA · Population 2,697,000 · Density 4,700/km²
About this scenario
This page calculates what would happen if the Trinity (USA, 1945) detonated over Chicago (USA). First nuclear test.
The third-largest city in the United States, anchoring the Midwest with a metro population of about 9.4 million. With an urban-core density of about 4,700 people per km², even a relatively small detonation over the city center would affect a large population.
The Trinity delivers 25 kt of explosive yield — 2× more powerful than the Hiroshima bomb. The tables below show calculated effect radii for an air burst (optimized for blast spread) and a surface burst (which produces massive fallout).
Air-burst effects (Trinity over Chicago)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.53 km | ~4,077 |
| Severe blast (20 PSI, ~98% fatal) | 1.39 km | ~24,055 |
| Moderate blast (5 PSI, ~50% fatal) | 2.98 km | ~51,191 |
| Light blast (1 PSI, glass injuries) | 8.48 km | ~46,485 |
| 3rd-degree thermal burns | 2.51 km | — |
| 2nd-degree thermal burns | 4.49 km | — |
Estimated total fatalities: ~79,323 · Estimated total affected (inside 1 PSI light-blast radius): ~1,060,775.
Surface-burst effects (with fallout)
A surface burst trades blast spread for radioactive fallout — much smaller blast radii but a large lethal fallout plume drifting downwind. This is what would happen if the Trinity struck ground level rather than detonating optimally above Chicago.
| Effect zone | Radius (surface burst) |
|---|---|
| Fireball | 0.42 km |
| Severe blast (20 PSI) | 0.77 km |
| Moderate blast (5 PSI) | 1.64 km |
| Light blast (1 PSI) | 4.66 km |
| 3rd-degree thermal burns | 1.50 km |
| Lethal fallout zone | ~43.5 km |
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See the actual blast zones overlaid on a map of Chicago with population-density-based casualty estimates updated in real time as you move the detonation point.
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FAQ
What would happen if the Trinity detonated over Chicago?
In an air burst over Chicago, the Trinity (25 kt) would produce a fireball about 0.53 km in radius. The 5 PSI moderate-blast zone — where most residential buildings collapse — would extend to 2.98 km. Light blast damage and shattered windows would reach 8.48 km. Given Chicago's urban density (~4,700/km²), this scenario yields an estimated 79,323 immediate fatalities and about 46,485 additional injured.
How many people would die in Chicago from a Trinity strike?
An air burst of the Trinity over Chicago could cause an estimated 79,323 immediate fatalities and 46,485 additional injuries. The fireball alone (radius 0.53 km) would kill approximately 4,077 people; the severe-blast zone (20 PSI, radius 1.39 km) would add 24,055; the moderate-blast zone (5 PSI, radius 2.98 km) would add 51,191 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Trinity on Chicago?
For an air burst over Chicago: fireball 0.53 km, severe blast (20 PSI) 1.39 km, moderate blast (5 PSI) 2.98 km, light blast (1 PSI) 8.48 km. Thermal radiation causes 3rd-degree burns out to 2.51 km. A surface burst would shrink the blast radii by roughly 40 percent but generate massive radioactive fallout extending ~43 km from ground zero.
Is the Trinity bigger than the bomb that hit Hiroshima?
The Hiroshima bomb (Little Boy) had a yield of about 15 kilotons. The Trinity at 25 kt is 2× more powerful than the Hiroshima bomb.