Trinity on Paris
25 kt fission weapon · France · Population 2,165,423 · Density 21,000/km²
About this scenario
This page calculates what would happen if the Trinity (USA, 1945) detonated over Paris (France). First nuclear test.
The capital of France and one of the most densely populated major cities in Europe; the Île-de-France region holds over 12 million people. With an urban-core density of about 21,000 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 Paris)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.53 km | ~18,216 |
| Severe blast (20 PSI, ~98% fatal) | 1.39 km | ~107,482 |
| Moderate blast (5 PSI, ~50% fatal) | 2.98 km | ~228,724 |
| Light blast (1 PSI, glass injuries) | 8.48 km | ~207,696 |
| 3rd-degree thermal burns | 2.51 km | — |
| 2nd-degree thermal burns | 4.49 km | — |
Estimated total fatalities: ~354,422 · Estimated total affected (inside 1 PSI light-blast radius): ~4,739,634.
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 Paris.
| 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 Paris 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 Paris?
In an air burst over Paris, 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 Paris's urban density (~21,000/km²), this scenario yields an estimated 354,422 immediate fatalities and about 207,696 additional injured.
How many people would die in Paris from a Trinity strike?
An air burst of the Trinity over Paris could cause an estimated 354,422 immediate fatalities and 207,696 additional injuries. The fireball alone (radius 0.53 km) would kill approximately 18,216 people; the severe-blast zone (20 PSI, radius 1.39 km) would add 107,482; the moderate-blast zone (5 PSI, radius 2.98 km) would add 228,724 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Trinity on Paris?
For an air burst over Paris: 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.