Trinity on Los Angeles
25 kt fission weapon · USA · Population 3,898,747 · Density 3,200/km²
About this scenario
This page calculates what would happen if the Trinity (USA, 1945) detonated over Los Angeles (USA). First nuclear test.
The second-most populous US city, sprawling across Southern California with a metro area of nearly 13 million. With an urban-core density of about 3,200 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 Los Angeles)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.53 km | ~2,776 |
| Severe blast (20 PSI, ~98% fatal) | 1.39 km | ~16,378 |
| Moderate blast (5 PSI, ~50% fatal) | 2.98 km | ~34,854 |
| Light blast (1 PSI, glass injuries) | 8.48 km | ~31,648 |
| 3rd-degree thermal burns | 2.51 km | — |
| 2nd-degree thermal burns | 4.49 km | — |
Estimated total fatalities: ~54,008 · Estimated total affected (inside 1 PSI light-blast radius): ~722,230.
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 Los Angeles.
| 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 |
Run this scenario in the simulator
See the actual blast zones overlaid on a map of Los Angeles 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 Los Angeles?
In an air burst over Los Angeles, 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 Los Angeles's urban density (~3,200/km²), this scenario yields an estimated 54,008 immediate fatalities and about 31,648 additional injured.
How many people would die in Los Angeles from a Trinity strike?
An air burst of the Trinity over Los Angeles could cause an estimated 54,008 immediate fatalities and 31,648 additional injuries. The fireball alone (radius 0.53 km) would kill approximately 2,776 people; the severe-blast zone (20 PSI, radius 1.39 km) would add 16,378; the moderate-blast zone (5 PSI, radius 2.98 km) would add 34,854 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Trinity on Los Angeles?
For an air burst over Los Angeles: 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.