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How Long Does Nuclear Fallout Last? Here’s Everything You Need to Know

It is natural to worry about a nuclear catastrophe, given the political turmoil unfolding across the globe in the last few years.

So how long does nuclear fallout last? While there is little you can do about nuclear warfare, you can protect yourself and your family from one of the bigger threats to humanity. But knowing how much time you’ll need to prepare to spend in a fallout shelter is a big part of that.

How long does nuclear fallout last?

Whether you’re a newly-minted survivalist or very familiar with the subject, this article will add to your knowledge and resolve any queries.

Let’s get started.

What Happens in a Nuclear Blast?

Nuclear blasts are explosions that occur upon the detonation of atomic bombs—a nuclear reaction that results in a big burst of energy radiation.

There is also a thermal flash that lasts a few seconds; dangerous because it is much hotter than the sun’s core. This flash then creates a blast wave that expands into the surroundings and destroys objects in its path. The shock wave can last a few seconds to several minutes.

A nuclear blast

There are many different after-effects based on the kind of nuclear weapons used and where they are detonated. Similarly, the radius of destruction and how long does nuclear fallout last also varies based on the weapon.

What Comes After a Nuclear Blast?

After the nuclear explosion and its shock wave have passed, the second stage—referred to as a nuclear fallout—follows. This is when radioactive material is propelled into the upper atmosphere, mainly dust and ash from the explosion.

If you’re wondering how long does nuclear fallout last, the immediate effects can last anywhere between three to five weeks. However, lingering radiation from fallout may last for decades.

Depending on where the blast occurs (air or ground), the scale and effects of the fallout may differ.

There is also the global cooling or nuclear winter that follows as a result of airborne smoke and soot clogging the upper atmosphere. This heavy cloud of nuclear waste will block sunlight, resulting in drastic global cooling much worse than the ice age.

How Long Does Nuclear Fallout Last?

How long does nuclear fallout last depends on many factors such as weapon design and yield, the nature of the explosion site, meteorological conditions, and more. The immediate lethal effects of a radioactive fallout can last a few days or several weeks.

While radiation levels continue to decrease as the fallout progresses, people must stay indoors for 24 to 48 hours to escape high levels of radiation. It may take a few months for energy radiation and contamination to go back to safe levels.

During this period, people can reduce radiation exposure by practicing safety procedures and staying indoors for most of the day.

How to Make a Fallout Shelter

There is no escaping from a nuclear disaster if it does happen. But emergency management precautions to save yourself and prevent severe damage during and after the fallout are quite easy to implement.

Fallout shelter

When you don’t know how long does nuclear fallout last, one way to ensure your safety is to create your own nuke shelter.

Choose the Perfect Location and Dig a Trench

The best place to build a nuke shelter is above or under stable ground and far away from obstructions. You can also build a shelter in a hill if you have access to one. You should also avoid areas with lots of trees, large bodies of water, flammable objects, or utility lines.

The shelter should be close enough to your place of residence so you can get there quickly in an emergency.

Once you’ve finalized the location, go to your county office and get all the permits required to build your structure. Then get a trencher and an excavator and start digging a trench.

Build Using the Right Building Material

The next step involves choosing the right materials to build your shelter. While many materials are used in construction, only a few can protect you during such a calamity.


Concrete is the most popular material for shelters due to its high compression strength. It is also a common building material used in almost all construction projects.

It has a long life, along with thermal insulation and impact resistance properties. These are all crucial since there is no way to know how long does nuclear fallout last.

Concrete for a fallout shelter

Its relatively affordable price makes it an excellent building material for your nuke shelter. The only drawback it has is low tensile strength.

Packed Earth

Also known as compacted soil, packed dirt effectively absorbs blast waves. It is also much cheaper than acquiring other construction materials. It is durable, low-maintenance, and pest-proof. It also has fire-resistant properties and protects against extreme temperatures.

Metal Sheets

Metal sheeting is durable and strong but relatively expensive. It is certainly the best product if your primary concern is water damage. The drawback is that these sheets do not provide good insulation; thus, you will have to use them in combination with insulating materials.

Steel Reinforced Concrete

Combining materials is a great solution for those looking to maximize their shelter’s protective layer.

Steel reinforced concrete is one such combination. It combines the compression and insulation qualities of concrete with the strength of steel.

Create a Strong Waterproof Shelter Roof

Whether you build a shelter in the ground or a hill, you benefit from the earth surrounding the floor and walls. What you do need to worry about is waterproofing.

On top of your base material, you can add a second layer of materials like rubberized asphalt and cementitious coatings. These durable materials are commonly used with concrete for commercial waterproofing applications.

Create an Emergency Exit With a Crawl-Way Entrance

Getting out can be challenging if your shelter is in the ground or a hill. Regardless of how long does nuclear fallout last, you may have to get out for many reasons, such as a fire inside the shelter, failure of the first entrance, a cave-in, or more.

Building an emergency exit is crucial to facilitate a safe exit in such situations. Place it at the opposite end of your main entrance and make it big enough for you to crawl through. Add dirt steps that lead to the exit to make it easier to access.

Shield Your Shelter

You must also shield your shelter and its entrance to prevent cave-ins and collapse. Some effective shielding methods include:


Shoring prevents the movement of soil, underground utilities, and other surrounding elements using support structures.


Sloping involves cutting the trench walls at an angle.

Have Clean Accessible Water

Stock up on plenty of large containers of water to sustain you through your time in the shelter. Opt for the largest containers that will fit in your shelter to limit wasted space.

Storing water in 5 gallon containers for nuclear fallout

If you have more time on your hands, building an off-grid water system should be your next priority.

Stock Up on Provisions

Pack an emergency supply kit for radiological emergency preparedness that you can take into the shelter while taking refuge.

It should include the following:

  • Bottled water
  • Packaged food
  • Medical supplies
  • Battery-powered radio
  • Flashlight
  • Extra batteries

Depending on how long does nuclear fallout last, you may have to take shelter for three to five weeks. Make sure your provisions will last until then.

Check out our guides for more tips on making oxygen absorbers for long-term food storage.

Make a Bomb Shelter for a Building

If you are inside a building during a nuclear attack, you must take shelter where you are and make the most of what’s available to you.

Find a Room of Concrete and Shield Walls With Sandbags if Possible

Try to find a room that’s made of concrete. It’s best to go for the basement or any room near the center of the structure.

Stack sandbags or other heavy objects against the windows, doors, and walls. These will help protect you from flying glass and reduce the potential for exposure to fallout.

Leave space between the sandbags near the entrance for ventilation.

Stock the Shelter with Provisions

While it may not always be possible to find provisions during an emergency, try to grab the following before entering a shelter:

  • Water bottles
  • Food supplies
  • Medical supplies
  • Battery-powered radio

You can also stock up on clothing items, personal hygiene items, and anything valuable you might find in the building. Again, there’s no way to know how long does nuclear fallout last—it’s better to have too many things than too few.

Where Are Nuclear Fallout Shelters in the U.S?

You can identify fallout shelters via symbols emblazoned on buildings.

Nuclear fallout shelter symbol

List of Nuclear Fallout Shelters

  • Cheyenne Mountain Complex, Colorado
  • Mount Weather Emergency Operations Center, Virginia
  • National Audio-Visual Conservation Center
  • Offutt AFB nuclear bunkers, Nebraska
  • Olney Support Center, Maryland
  • Post-Attack Command and Control System (PACCS)
  • Post-Attack Command and Control System Facility, Hadley
  • Project Greek Island, West Virginia
  • Raven Rock Mountain Complex, Pennsylvania
  • Selfridge AFB radar station, Michigan
  • Super Combat Center (SCC)
  • Template: US POTUS Emergency Posts
  • Warrenton Training Center, Virginia
  • White Sulphur Springs, West Virginia

Most of the radioactive fallout shelters worldwide were built during the cold war. Many were later converted into museums, banks, or historical landmarks.

List of Caves to Survive a Nuclear Explosion

There are plenty of caves in every state where you can take shelter. Here are a few located in cities most likely to get hit:

  • Cave of the Winds, New York
  • Cave-in-Rock, Illinois
  • Ape Cave, Washington D.C.
  • Mitchell Caverns, Los Angeles
  • Moaning Cavern, San Francisco
  • Longhorn Cavern, Houston
  • Wind Cave, North Dakota
  • Lewis and Clark Caverns, Montana

Things to Do After a Nuclear Fallout

Get Safely Inside

If you are outdoors during nuclear detonations, seek cover from the nuclear blasts or lie on the ground and cover your face and body.

Run indoors as quickly as possible, ideally within 10 minutes.

Stay Inside Away From Windows

Once indoors, make sure to cover all entrances to the room and stay away from the windows. They offer no protection against radiation from fallout and might easily break and hurt you.

Stay Connected

Turn on a radio or television to watch the news and stay in touch with the local authorities. This will help you get your bearings and coordinate your movements for a safe evacuation.

Wear a Mask And Social Distance

Make sure to wear a mask or use a damp cloth to cover your face no matter how long does nuclear fallout last. Also, maintain a distance of six feet between people not part of your household.

Decontaminate Yourself

Once you’re in the shelter, make sure to decontaminate yourself by removing the outer layer of clothing and taking a shower with soap and water. Repeat this every time you step out.

Frequently Asked Questions

How long would you need to stay inside after a nuclear fallout?

At least three to five weeks, regardless of how long does nuclear fallout last.

While the walls of your home can protect you from harmful nuclear radiation, it is crucial to stay inside for three to five weeks before traveling anywhere.

Nuclear fallout can last a long time

If you must get out for resources, the United States Government advises people to wait at least 24 hours after a nuclear weapon detonation.

What materials can block radiation?

Some of the materials that can block gamma rays include:

  • Lead
  • Tungsten
  • Concrete
  • Sand
  • Dirt

How can you get fresh air to breathe in an underground bunker?

You can get fresh air in an underground bunker using methods and equipment like:

  • NBC filters
  • Growing plants inside the bunker (that require little water and sunlight)

Wrapping Up: How Long Does Nuclear Fallout Last?

The effects of a single nuclear explosion are hard to predict, as the impact on the environment and humanity is determined by many elements that are nearly impossible to predict.

Our recommendations have closely considered the many possibilities and will still keep you safe in the event of this calamity.

We hope our guide has cleared your doubts and misconceptions about nuclear bombs and that you now know how to protect yourself after an attack.

To find out more about how long does nuclear fallout last and how to survive during one, visit Survival World.