Heat

When a nuclear weapon is detonated, it releases extreme heat. Almost everything and everyone close to ground zero is instantly reduced to ash and vapour.

A large fireball, over a million degrees Celsius at its core, rises high into the sky, and ground temperatures reach several thousand degrees – hotter than the surface of the Sun.

The extreme heat ignites fires across a wide area, which release toxic smoke and combustion gases into the air and coalesce to form a giant firestorm.

Even people who are tens of kilometres away from ground zero suffer severe, life-threatening burns, while people much further away are blinded by the bright flash of light.

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Blast

A nuclear weapon also generates an immense, fast-moving wall of high-pressure air known as a shock wave, which moves outwards for many kilometres.

It hurls people through the air, knocks them unconscious, rips their bodies apart and causes their lungs to collapse.

Buildings across a wide area are completely flattened, and many people are crushed to death. Loose objects are tossed through the air like missiles.

Even large concrete and steel skyscrapers are destroyed by the force of the blast.

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Radiation

The nuclear chain reaction that causes the explosion releases a massive amount of ionising radiation, which penetrates deep into people’s bodies, destroying or damaging their cells and inducing disease.

Even at a distance of several kilometres from ground zero, people receive a dose of radiation high enough to cause death from acute radiation poisoning.

Symptoms include vomiting, bleeding gums, diarrhoea and hair loss. Most sufferers die within a couple of months of the attack.

Some recover from the acute stage of the illness but die years or even decades later from cancers and other illnesses caused by the delayed effects of radiation.

Some survivors exhibit chromosomal aberrations and other types of genetic damage, which can be passed on to future generations.

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Fallout

A nuclear weapon also creates an enormous mushroom cloud, which sucks up radioactive dust and debris in a column and releases it into the atmosphere.

Wind currents disperse it through the air, and it eventually falls to the ground over a vast area.

Known as fallout, it poses immediate and long-term health risks even to people far away from ground zero. Some radioactive isotopes remain hazardous for many years, contaminating the soil, water and food supplies.

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Electromagnetic pulse

If detonated at a high altitude, a nuclear weapon emits a powerful electromagnetic pulse, which destroys electronics over a wide area. Cellular communications, internet capabilities and banking technology are all severely disrupted.

This effect was first observed during the era of atmospheric and high-altitude nuclear testing. In 1962, when the United States tested a nuclear weapon in outer space about 400 kilometres above Johnston Atoll in the Pacific Ocean, it caused damage to streetlights and phones in Hawaii, more than 1,450 kilometres away.

A very high-yield, high-altitude nuclear explosion could destroy electronics across an entire continent.

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[VIDEO]https://assets.nationbuilder.com/ican/pages/12221/attachments/original/1776879547/video-explosion.mp4?1776879547[/VIDEO]

[CAPTION]The blast effects of a nuclear test explosion on a mock house in the US state of Nevada. Credit: US government[/CAPTION]