Effects of a Nuclear Explosion

A nuclear detonation attacks everything around it through several distinct mechanisms, arriving one after another in the first seconds and minutes. These are exactly the rings the simulator draws on the map.

The fireball

Within a millionth of a second the weapon's energy is concentrated in a ball of plasma hotter than the core of the Sun. For a 1-megaton burst the fireball grows to roughly two kilometres across. Everything inside it is vaporised. If the fireball touches the ground, enormous amounts of soil are drawn up and irradiated — this is what turns an explosion «dirty» with local fallout.

Thermal radiation: the flash

For several seconds the fireball shines with an intense heat pulse travelling at the speed of light. Near the burst it ignites fires; farther out it causes third-, second- and first-degree burns on exposed skin — for a megaton-class weapon, serious burns occur many kilometres away, far beyond the zone of building collapse. The flash is also bright enough to cause temporary or permanent blindness in people who happen to be looking toward it.

The blast wave

About half the weapon's energy goes into a shock front of compressed air, followed by hurricane-force winds. Damage is measured in overpressure: at 20 psi even reinforced concrete structures are levelled; at 5 psi ordinary houses collapse and injuries are universal; at 1 psi windows shatter — dangerous in itself, because the flash arrives first and draws people to the glass. The blast wave takes tens of seconds to reach the outer rings, so knowing to take cover after a flash genuinely saves lives.

Initial nuclear radiation

The first minute delivers an intense burst of neutrons and gamma rays. A dose above ~500 rem is usually fatal without treatment. For small weapons this radius extends beyond the blast damage; for large ones it is buried deep inside zones where nothing survives anyway.

Electromagnetic pulse

Gamma rays interacting with the atmosphere create a powerful electromagnetic pulse. A high-altitude burst can knock out electronics and power grids across an area of continental scale, even where no other effect is felt on the ground.

Radioactive fallout

A surface burst lofts thousands of tons of irradiated debris into the mushroom cloud. Heavier particles rain back down within hours along the wind direction, producing a plume where accumulated doses can be lethal for people in the open. Dose rates fall quickly — by the «7:10 rule», every seven-fold increase in time cuts the dose rate ten-fold — which is why sheltering for even the first day or two dramatically improves survival. An airburst whose fireball never touches the ground produces almost no local fallout; compare both modes in the simulator.

Long-term consequences

Survivors of significant radiation exposure face elevated lifetime cancer risk, as documented in decades of studies of the Hiroshima and Nagasaki survivors. A large-scale nuclear exchange would additionally loft enough soot to cool the global climate — the «nuclear winter» scenario — threatening agriculture worldwide. The methodology behind each modelled effect is described here.