If a nuclear bomb goes off, this is the most important thing you can do to survive

The Cold War ended in 1991, but the looming threat of nuclear attack lives on with more than 14,900 nuclear weapons wielded by nine nations.

A terrorist-caused nuclear detonation is one of 15 disasters scenarios that the federal government continues to plan for with state and city governments — just in case.

"National Planning Scenario No. 1 is a 10-kiloton nuclear detonation in a modern US city," Brooke Buddemeier, a health physicist and expert on radiation at Lawrence Livermore National Laboratory, told Business Insider. "A 10-kiloton nuclear detonation is equivalent to 5,000 Oklahoma City bombings. Though we call it 'low yield,' it's a pretty darn big explosion."

Buddemeier said the likelihood of such an attack was "one of these things that changes with time."

However, it's not an unfounded concern, with the proliferation of fissile nuclear material and kiloton-class weapons in stockpiles.

If a nuclear detonation were to occur, and you somehow avoided the searing bright flash, crushing blast wave, and incendiary fireball, Buddemeier says one simple thing could increase your odds of survival.

"Shelter, shelter, shelter," he said. "The same place you would go to protect yourself from a tornado is a great place to go."

What you'd be hiding from is sandy and deadly, and it would arrive in minutes.

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How to survive a nuclear attack
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How to survive a nuclear attack

What should you do in the event of a nearby nuclear attack? Click through to learn more. 

(Photo by Lambert/Getty Images)

Seek shelter immediately, towards the center of a building or -- preferably -- a basement. Aim for the same type of shelter you would utilize in the event of a tornado. 

(Photo via Getty Images)

The next three slides are examples of nuclear shelters that exist around the world. 

(Image via Lawrence Livermore National Laboratory)

The entrance of Shelter Co.'s nuclear shelter model room, which is placed in the basement of the company's CEO Seiichiro Nishimoto's house, is pictured in Osaka, Japan April 26, 2017. (Photo via REUTERS/Kim Kyung-Hoon)
A fallout shelter sign hangs on the Mount Rona Baptist Church, on August 9, 2017 in Washington, DC. In the early 60's Washington was at the center of civil defense preparations in case of a nuclear blast, with over one thousand dedicated public fallout shelters in schools, churches and government buildings. (Photo by Mark Wilson/Getty Images)
A 'shelter' sign is displayed at the entrance to a subway station in Seoul on July 6, 2017 in Seoul, South Korea. According to the metropolitan government, South Korea's city subway stations serve a dual purpose with over 3,300 designated as shelters in case of aerial bombardment including any threat from North Korea. The U.S. said that it will use military force if needed to stop North Korea's nuclear missile program after North Korea fired an intercontinental ballistic missile on Tuesday into Japanese waters. The latest launch have drawn strong criticism from the U.S. as experts believe the ICBM has the range to reach the U.S. states of Alaska and Hawaii and perhaps the U.S. Pacific Northwest. (Photo by Chung Sung-Jun/Getty Images)

Dense materials, including dirt or thick walls, provide the best defense to fallout radiation.

(Photo via Getty Images)

If possible, take a warm shower -- but do not use conditioner, as it can bond to nuclear particles. 

(Photo via Getty Images)

Do not seek shelter in a car, as they won't provide adequate protection, and you should not attempt to outrun nuclear fallout. 

(Photo by Noel Hendrickson via Getty Images)

The nuclear fallout zone shrinks quickly after an attack, but the less dangerous "hot zone" still grows. 

(Image via Lawrence Livermore National Laboratory)

Once you are sheltered, do not leave. Listen to a radio or other announcements. 

(Photo via Getty Images)

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The threat of radioactive fallout

A fearsome aftereffect of nuclear blasts is fallout, which is a complex mixture of fission products (or radioisotopes) created by splitting atoms.

Many of these fission products decay rapidly and emit gamma radiation — an invisible yet highly energetic form of light. Exposure to too much of this radiation in a short time can damage the body's cells and its ability to fix itself, which is a condition called acute radiation sickness.

"It also affects the immune system and your ability to fight infections," Buddemeier said.

Only very dense and thick materials, like many feet of dirt or inches of lead, can reliably stop the gamma radiation emitted by fallout.

"The fireball from a 10-kiloton explosion is so hot, it actually shoots up into the atmosphere at over 100 miles per hour," Buddemeier said. "These fission products mix in with the dirt and debris that's drawn up into the atmosphere from the fireball. ... What we're talking about is 8,000 tons of dirt and debris being drawn up into this cloud."

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Satellite images of the Punggye-ri nuclear test site in North Korea
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Satellite images of the Punggye-ri nuclear test site in North Korea
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - APRIL 2, 2017. Figure 1. Activity continues at the North Portal. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - APRIL 2, 2017. Figure 2. Possible new dumping observed at the North Portal spoil pile. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - APRIL 2, 2017. Figure 3. Probable personnel in formation or equipment in rows at the Main Administrative Area. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 30, 2017. Figure 1. No vehicles or trailers remain around the North Portal but well-worn paths are observed. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 30, 2017. Figure 2. No new dumping of material on the North Portal spoil pile. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 30, 2017. Figure 3. Small collection of crates or trailers seen in previous imagery has been removed. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 28, 2017. Figure 3B. Formations seen in the Main Administrative Area, similar to what was seen in lead up to 2013 nuclear test. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 28, 2017. Figure 2. Material dumped at the North Portal tailings pile. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - JANUARY 4, 2013. Figure 3A. Formations seen in the Main Administrative Area in lead up to 2013 nuclear test. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 28, 2017. Figure 1. Continued activity at the North Portal. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 25, 2017. Figure 1. Probable cabling and water drainage seen at the North Portal. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - OCTOBER 19th, 2016: Figure 6: Excavation continued underground in the North Portal area suggesting more tests to come in the same tunnel complex directly under Mt. Mantap. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - JANUARY 5th, 2017: Figure 7: The North Portal spoil pile continued to expand into 2017, becoming increasingly broader. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - JANUARY 22nd, 2017: Figure 8: Late January 2017 imagery showing new spoil on top of recent snow. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - OCTOBER 19th, 2016: Figure 9. A close-up of the North Portal spoil pile as it appeared in late October 2016. The unstable spoil can sometimes lead to accidents, as in this case of toppled rail cars downslope. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - FEBRUARY 12th, 2017: Figure 10. A close-up of the North Portal spoil pile from February 2017 shows that accumulations had begun move westward with a broadening of the top and bottom west side of the pile. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 1. DigitalGlobe imagery showing large shipping container or crate seen at the North Portal. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 2. DigitalGlobe imagery showing no changes to pattern and texture of tailings (spoil) pile at the North Portal. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 3. DigitalGlobe imagery showing a small vehicle present at the West Portal. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 4. DigitalGlobe imagery showing a truck present in the southern courtyard of the Main Administrative Area. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 5. DigitalGlobe imagery showing a truck present at the sites Command Center. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - MARCH 7th, 2017: Figure 6. DigitalGlobe imagery showing snow cleared at guard barrack and security checkpoint. Date: March 7, 2017. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - OCTOBER 24, 2016: Figure 2. No activity seen at the Sohae launch pad. Date: October 24, 2016. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - OCTOBER 24, 2016: Figure 3. Environmental shed remains adjacent to the vertical engine test stand. (Photo DigitalGlobe/38 North via Getty Images)
PUNGGYE-RI NUCLEAR TEST SITE, NORTH KOREA - OCTOBER 29, 2016: Figure 1C. Increased activity around the North Portal throughout October. Date: October 29, 2016. (Photo DigitalGlobe/38 North via Getty Images)
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The gamma-shooting fallout can loft more than five miles into the air. Larger chunks and pieces quickly rain back down, but the lighter particles can be sprinkled over distant areas.

"Close into the [blast] site, they may be a bit larger than golf-ball-size, but really what we're talking about are things like salt- or sand-size particles," Buddemeier said, adding that fallout doesn't resemble snow or dust, as movies often depict. "It's the penetrating gamma radiation coming off of those particles that's the hazard."

A car is the least ideal place to shelter for a variety of reasons, Buddemeier says.

For one, "your ability to know where the fallout's gonna go, and outrun it, are — well, it's very unlikely," he said, because it would be carried by high-altitude winds "often booking along at 100 miles per hour."

Plus, streets would probably be full of erratic drivers, accidents, and debris, and some vehicles may not work because of a strange effect called electromagnetic pulse, or EMP.

But most importantly, you shouldn't "assume that the glass and metal of a vehicle can protect you" from fallout, Buddemeier says. "Modern vehicles are made of glass and very light metals, and they offer almost no protection. You're just going to sit on a road someplace" and be exposed.

A much better shelter would most likely be within a quick walk or run of wherever you may be, Buddemeier says, and "the timing is important."

Where you should shelter from fallout

Your best shot at survival after a nuclear disaster would be to immediately get into a "robust structure" and stay there. Buddemeier is a fan of the mantra "go in, stay in, tune in."

"Get inside ... and get to the center of that building," he said. "If you happen to have access to belowground areas, getting below ground is great."

Besides cars, the poorest shelters are made of wood, plaster, and other materials that wouldn't shield much radiation — about 20% of houses fall into this category. Better shelters, such as schools and offices, are made of bricks or concrete and have few or no windows.

Soil is a great shield from radiation, Buddemeier says, so ducking into a home with a half basement would be better than going into a place with no basement at all.

Next, "stay in 12 to 24 hours," he said.

The reason to wait is that levels of gamma and other radiation fall off exponentially after a nuclear blast, as hot radioisotopes decay into stable atoms. This slowly shrinks the dangerous fallout zone — the area where high-altitude winds have dropped the most radioactive fission products.

19 PHOTOS
Inside a nuclear bunker in Japan
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Inside a nuclear bunker in Japan
Seiichiro Nishimoto, CEO of Shelter Co., wears a gas mask as he presents the model room for the company� nuclear shelters during an interview with Reuters in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
A toilet is pictured in Shelter Co.'s nuclear shelter model room in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., poses wearing a gas mask at a model room for the company� nuclear shelters in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon TPX IMAGES OF THE DAY
Seiichiro Nishimoto, CEO of Shelter Co., demonstrates how to use the exit of Shelter Co.'s nuclear shelter model room installed in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., walks into a basement where the model room for the company� nuclear shelters is installed during an interview with Reuters in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
The house of Seiichiro Nishimoto, president of the Shelter Co., where the model room for the company� nuclear shelters is installed, is pictured in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., poses in front of a blast door at the entrance of a model room for his company� nuclear shelters during an interview with Reuters in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., demonstrates how to use a radiation-blocking air purifier in case of power outage at the model room for Shelter Co.'s nuclear shelters in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Emergency foods are seen in the model room of Shelter Co.'s nuclear shelter in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Radiation-blocking air purifiers are seen in the model room of Shelter Co.'s nuclear shelter in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., demonstrates how to use a radiation-blocking air purifier in case of power outage at the model room for Shelter Co.'s nuclear shelters in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
A gas mask, a Geiger counter and emergency goods are seen in Shelter Co.'s nuclear shelter model room in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Radiation-blocking air purifiers are seen in the model room of Shelter Co.'s nuclear shelter in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
A blast door is seen at the entrance of Shelter Co.'s nuclear shelter model room, placed in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
The entrance of Shelter Co.'s nuclear shelter model room, which is placed in the basement of the company's CEO Seiichiro Nishimoto's house, is pictured in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., poses wearing a gas mask at a model room for the company� nuclear shelters in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
The exit of Shelter Co.'s nuclear shelter model room is pictured in the basement of its CEO Seiichiro Nishimoto's house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
Seiichiro Nishimoto, CEO of Shelter Co., poses wearing a gas mask at a model room for the company� nuclear shelters in the basement of his house in Osaka, Japan April 26, 2017. REUTERS/Kim Kyung-Hoon
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A recent study by Michael Dillon, a colleague of Buddemeier's at LLNL, suggests that moving to a stronger shelter or basement may not be a bad idea if you initially ducked into a flimsy one. But whatever structure you're moving to should be less than five minutes away. (Though if you're very close to the blast site, stay put in whatever you can find.)

Finally, tune in.

"Try to use whatever communication tools you have," Buddemeier said, adding that a hand-cranked radio is a good object to keep at work and home, since emergency providers would be broadcasting instructions, tracking the fallout cloud, and identifying where any safe corridors for escape could be.

Despite the fearsome power of a nuclear EMP, which has the potential to damage electronics, "there is a good chance that there will be plenty of functioning radios even within a few miles of the event" that could provide "information on the safest strategy to keep you and your family safe," Buddemeier said.

Buddemeier says he hopes no one will ever have to act on his advice. But if people could find good shelters, he says, the blow of a catastrophe could be softened.

"We may not be able to do much about the blast casualties, because where you were is where you were, and you can't really change that. But fallout casualties are entirely preventable," he said. "In a large city ... knowing what to do after an event like this can literally save hundreds of thousands of people from radiation illness or fatalities."

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