How Far Away Do You Have to Be to Survive a Nuclear Blast?

It has been nearly 80 years since two nuclear bombs were dropped on the Japanese cities of Hiroshima and Nagasaki, killing at least 129,000 people and generating long-term health consequences.

To date, those are the only instances of nuclear bombs being used in battle, but there are around 12,700 warheads still in the globe. So, what if a nuclear war broke out tomorrow?

Don’t be alarmed; this is merely a hypothetical. However, in the video below, the AsapSCIENCE team delves down the science of nuclear bombs to forecast your chances of survival. Let’s just say that in the event of a nuclear blast, you’d want to be dressed in white.

To begin, let me state unequivocally that there is no clear-cut way to estimate the impact of a single nuclear bomb because it is dependent on numerous factors, including the weather on the day it is dropped, the time of day it is detonated, the geographical layout of where it hits, and whether it explodes on the ground or in the air.

However, there are some predictable stages of a nuclear weapon blast that can alter your chances of survival. (You can also use this terrifying interactive to see how a nuclear blast would travel over your neighborhood.)

According to the video above, thermal radiation accounts for around 35% of the energy produced by a nuclear bomb. Because thermal radiation travels at approximately the speed of light, the first thing you will notice is a blinding flash of light and heat.

The light alone is enough to create flash blindness, a transient form of vision loss that can last a few minutes.

The AsapSCIENCE movie explores a 1 megaton explosion, which is 80 times greater than the Hiroshima bomb but far smaller than many existing nuclear weapons.

On a clear day, those up to 21 km (13 miles) away would experience flash blindness, and people up to 85 km (52.8 miles) away would be temporarily blinded.

Heat is an issue for people who are near to the explosion. Mild, first-degree burns can happen up to 11 km (6.8 miles) distant, while third-degree burns, which damage and blister skin tissue, can happen up to 8 km (5 miles). Third-degree burns that cover more than 24 percent of the body are likely to be fatal if patients do not seek medical attention very once.

Those distances vary depending on not only the weather, but also what you’re wearing – white garments can reflect some of the energy of a blast, whilst darker clothes absorb it.

That is unlikely to make a significant difference for anyone unfortunate enough to be near the epicenter of the explosion.

Temperatures around the site of the Hiroshima bomb blast were estimated to exceed 300,000 degrees Celsius (540,000 degrees Fahrenheit) – roughly 300 times hotter than the temperature at which bodies are burnt, thus individuals were almost instantly transformed to the most basic elements, such as carbon.

Aside from heat, individuals who are slightly further out from the core of the blast must consider other repercussions. The force of a nuclear explosion also propels air away from the explosion site, causing abrupt changes in air pressure that can crush items and knock down structures.

Blast waves from a 1-megaton bomb would exert 180 metric tons of force on the walls of all two-story buildings within a 6-kilometer (3.7-mile) radius, with wind speeds of 255 km/h (158 mph). Peak pressure is four times that amount in a 1-km (0.6-mile) radius, and wind speeds can reach 756 km/h (470 mph).

Humans can technically survive so much pressure, however the majority of people would be killed by falling structures.

If you survive all of that, you’ll have to deal with radiation illness and nuclear fallout. AsapSCIENCE mentions this in the video above, but the long-term impacts on the planet are more severe than you might think.

A 2019 simulation research, for example, revealed that a nuclear war between the United States and Russia would plunge Earth into a nuclear winter within days due to the volumes of smoke and soot discharged into the sky.

We also know that radioactive particles may go a long distance; a recent research discovered traces of radioactive carbon from Cold War nuclear bomb tests all the way down in the Mariana Trench, the world’s lowest point in the oceans.

Again, this is all hypothetical; there are international conventions in place to prevent the spread and use of nuclear weapons, so we hope you never need to know any of this information in the real world.

To learn more about the current state of nuclear weaponry around the world, including the size of the bombs, go to the Nuclear Notebook at the Bulletin of Atomic Scientists.