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

Updated

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.

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."

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.

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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