Fat Man on Melbourne
21 kt fission weapon · Australia · Population 5,078,000 · Density 2,500/km²
About this scenario
This page calculates what would happen if the Fat Man (USA, 1945) detonated over Melbourne (Australia). Nagasaki bomb.
The second-largest city in Australia and capital of the state of Victoria. With an urban-core density of about 2,500 people per km², even a relatively small detonation over the city center would affect a large population.
The Fat Man delivers 21 kt of explosive yield — comparable in yield to 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 (Fat Man over Melbourne)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.49 km | ~1,886 |
| Severe blast (20 PSI, ~98% fatal) | 1.32 km | ~11,452 |
| Moderate blast (5 PSI, ~50% fatal) | 2.81 km | ~24,269 |
| Light blast (1 PSI, glass injuries) | 8.00 km | ~22,038 |
| 3rd-degree thermal burns | 2.33 km | — |
| 2nd-degree thermal burns | 4.18 km | — |
Estimated total fatalities: ~37,607 · Estimated total affected (inside 1 PSI light-blast radius): ~502,910.
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 Fat Man struck ground level rather than detonating optimally above Melbourne.
| Effect zone | Radius (surface burst) |
|---|---|
| Fireball | 0.39 km |
| Severe blast (20 PSI) | 0.72 km |
| Moderate blast (5 PSI) | 1.55 km |
| Light blast (1 PSI) | 4.40 km |
| 3rd-degree thermal burns | 1.40 km |
| Lethal fallout zone | ~40.6 km |
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See the actual blast zones overlaid on a map of Melbourne 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 Fat Man detonated over Melbourne?
In an air burst over Melbourne, the Fat Man (21 kt) would produce a fireball about 0.49 km in radius. The 5 PSI moderate-blast zone — where most residential buildings collapse — would extend to 2.81 km. Light blast damage and shattered windows would reach 8.00 km. Given Melbourne's urban density (~2,500/km²), this scenario yields an estimated 37,607 immediate fatalities and about 22,038 additional injured.
How many people would die in Melbourne from a Fat Man strike?
An air burst of the Fat Man over Melbourne could cause an estimated 37,607 immediate fatalities and 22,038 additional injuries. The fireball alone (radius 0.49 km) would kill approximately 1,886 people; the severe-blast zone (20 PSI, radius 1.32 km) would add 11,452; the moderate-blast zone (5 PSI, radius 2.81 km) would add 24,269 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Fat Man on Melbourne?
For an air burst over Melbourne: fireball 0.49 km, severe blast (20 PSI) 1.32 km, moderate blast (5 PSI) 2.81 km, light blast (1 PSI) 8.00 km. Thermal radiation causes 3rd-degree burns out to 2.33 km. A surface burst would shrink the blast radii by roughly 40 percent but generate massive radioactive fallout extending ~41 km from ground zero.
Is the Fat Man bigger than the bomb that hit Hiroshima?
The Hiroshima bomb (Little Boy) had a yield of about 15 kilotons. The Fat Man at 21 kt is comparable in yield to the Hiroshima bomb.