On Aug. 8, residents of Severodvinsk, Russia, witnessed a tremendous explosion. Experts across the world are still trying to piece together exactly what happened—and Russian media outlets are demanding answers from the Kremlin—but it seems clear the explosion came from somewhere close to the Russian Navy’s nearby missile-testing range.

The current theory is that the blast, which killed five scientists and blanketed the immediate region with a still-unknown amount of radiation, most likely involved a missile equipped with a miniature nuclear reactor.

Though the incident doesn’t seem to have involved a live nuclear warhead, submarines armed with such weapons are a key component of Russia’s nuclear deterrence strategy—same as in the United States. And following the collapse earlier this year of the Intermediate-Range Nuclear Forces treaty that limited weapons-testing, the world may see more and more nuclear weapons tests. With them comes the increased likelihood of accidents and exposure to radiation.

As anyone who watched HBO’s Chernobyl miniseries this spring can tell you, massive releases of radiation are also possible in entirely peaceful scenarios. Maybe the next catastrophe will be the result of engineering mistakes and human error, like Chernobyl was. Or perhaps a natural disaster will lead to a nuclear accident, like the earthquake that triggered reactor meltdowns at Japan’s Fukushima Daiichi Nuclear Power Plant in 2011.

Know your risk

Maybe the likelihood of being affected by a nuclear event seems too low for you to even consider worrying, but know that the most likely scenario involves exposure to radiation from a nearby source. So ascertain if there’s one nearby. If you live in Pennsylvania, for example, you probably already know if your home is one of the 40 percent of Keystone State residences exposed to radon gas. Those who live near an old uranium mine, a disused weapons-testing or weapons-assembly plant, or any of the nearly 100 radioactive locations on the Department of Energy’s “legacy management” list are probably equally well-informed.

The same is true with commercial nuclear power plants. If you’re one of the roughly 3 million Americans living within 10 miles of an energy-generating reactor, you’re inside an “emergency planning zone” designated by the Nuclear Regulatory Commission.

But if there is actually a mishap at a reactor, the effects will be much more widespread, says Edwin Lyman, a physicist and nuclear power safety and security expert at the Union of Concerned Scientists. Some experts say anyone within 50 miles of a nuclear power plant or research facility should be prepared to take immediate action. That means 65 percent of Americans, including nearly every resident of New York City, could be at risk.

“You can’t count on the industry or the Nuclear Regulatory Commission to fully evaluate the potential consequences, because they put a lid on the events they actually worry about,” Lyman says. “That also puts people at risk.” The NRC—who’s had a long history of friction with the UCS—challenges Lyman’s claims and says it has strict guidelines to let people know in less than an hour when a significant event takes place in nuclear power plants or research facilities accross the country. “The idea that the NRC prevents the public from learning about events at nuclear power plants, is incorrect,” says Scott Burnell, public affairs officer at the commission.

In either case, it’s easy to figure out by yourself if you live closer than 50 miles from a nuclear reactor. It may be a little more challenging to determine if there’s a weapons or enrichment facility nearby, but it can be done. Most weapons-assembly and research facilities, like the Idaho National Laboratory, are in relatively isolated areas and are not exactly open to the public. Though exactly what they do is a matter of national security, their existence isn’t a state secret.

Knowing whether you’re in an area likely to be targeted by a nuclear weapon is much easier: If you live somewhere populated, or with important military installations, you are.

And while understanding your risk doesn’t mean we should all be rushing to construct fallout shelters and stock up on Geiger counters, it’s still important to know how to react. The chance of a nuclear disaster may be low, but the cost is profound.

“They are events that may never happen, but if they do happen, the extent of the damage—in human, economic, and social terms—may be extraordinary,” says Alex Wellerstein, a professor at the Stevens Institute of Technology and an expert on the history of nuclear weapons.

a ferris wheel in Pripyat, Ukraine, near Chernobyl
Fifty thousand people used to live in this city. Now, it’s a ghost town. Ilja Nedilko via Unsplash

In most natural disasters, the first rule is to stay informed and follow instructions from local authorities. But in the event of a nuclear threat, government officials may not be the best source for accurate information and appropriate measures, experts say. As the Russians are currently demonstrating, secrecy and obfuscation characterize every nuclear weapons program (including the United States’), and, according to experts contacted for this article, there remains an imperative to downplay the severity of commercial accidents—officials simultaneously want to avoid panic and preserve the industry’s reputation.

That means it’s largely up to you to protect yourself. Preparedness and awareness are key, but even if you’ve just moved and have barely unpacked, there are measures you can take to reduce your risk of radiation exposure and (hopefully) your likelihood of suffering radiation sickness or developing cancer.

Understand radiation

First, try to pierce through the confusion. Know the difference between radioactive material and radiation itself. Many natural things are radioactive—the granite at Grand Central Station in New York City, for example, has minute traces of uranium—but you’ll only be in danger if you are exposed to a constant level of radiation over a long period of time, or if the radioactive material emanates a significant amount of radiation.

Radiation is energy: the waves and particles cast into the environment by a radioactive object or nuclear event. Anything more than 50,000 millirem—a massive dose compared to the 620 millirem absorbed annually by the average American—tends to start to kill cells.

In short: Nuclear events are short-lived, but incredibly dangerous; radioactive objects are more common, but far less threatening.

a damaged nuclear radiation hazard warning sign in Pripyat, Ukraine
Events like Chernobyl don’t last long, but their devastating effects can continue for decades. Ilja Nedilko via Unsplash

One direct countermeasure you can take when exposed to radiation is to pop a tablet of pop a tablet of potassium iodide—the FDA has specific guidelines to do so. If you live near a reactor, your state might already stockpile the stuff, but not every state does. You can also buy your own. Taking a potassium iodide pill in the first few hours after an event may protect your thyroid gland from absorbing too much radioactive iodine, but it won’t be much help in protecting the rest of your internal organs.

Knowing how radiation works is also helpful. It’s invisible—you can’t see, smell, or taste it—but you can learn how it moves. Radioactive contamination travels by water—as in rain or streams—or air, so think of it like snow or ash and treat it the same way, Wellerstein says.

Which means…

Get inside and stay there

Even if you live in a major population center that’s hit with a relatively low-yield nuclear weapon of about 10 kilotons—smaller than the bombs dropped on Hiroshima and Nagasaki, and a tiny fraction of the nine-megaton Cold War-era bombs designed to destroy Soviet cities—you can survive if you take prudent action.

“And if you are very, very lucky,” says Ferenc Dalnoki-Veress, a professor at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies.

If you’re not already dead, on fire, or in a building that is—very likely outcomes of a nearby nuclear explosion—you’ve got work to do.

As quickly as you can, get inside and stay there. For days, if necessary.

a dark, creepy basement with some coolers in it
Normally, you probably wouldn’t want to hang out in a place like this. But during a nuclear event, it might feel like a five-star hotel. Isaac Jarnagin via Unsplash

Places like schools or government buildings are the best places to shelter. These are more likely to be built of concrete, masonry, and steel, which makes them better at keeping ionizing radiation away than, say, a wood-framed house. Even small American towns and cities have post offices or libraries made of stone. The more insulation between you and the outdoors, the better—a basement is preferable to a top floor, and a room away from windows or doors is superior to a balcony.

The good news is that the half-life of a nuclear event’s most dangerous particles is a few days—maybe a week. That means staying indoors for up to three days may be enough to significantly reduce your risk of absorbing a damaging or fatal dose, but it also means you ought to have stockpiled enough canned food and water for a long weekend’s worth of living-room camping.

Just in case, you should be doing that anyway: Experts say you should be prepared to survive on your own for up to 72 hours after a disaster—about the time it takes authorities to muster an “official” response.

Get clean

If you were outside when the event occured, you can reduce your radiation exposure by doing basic chores, like laundering your clothes and taking a shower. Radioactive material that beams damaging alpha, beta, and gamma particles into your body clings to clothing and skin, but it can be washed off, reducing your exposure. If you’re already the type who removes your shoes before entering your house and tracking dirt around, you’re a step ahead.

Improve your shelter

a boarded up house on open land
Aesthetics really don’t matter when you’re trying to hide from nuclear radiation. Dan Meyers via Unsplash

Sure, a wood-framed house with drafty windows and cracks in the walls isn’t great shelter, but you can make it slightly better shelter by staying away from anything that’s letting air (and radiation) in, or closing them. Something as simple as hanging a sheet over a window or placing plywood over a door can still make a difference.

“Any space you can put in between yourself and the event, anything—even just air, or a few feet of wood—is going to absorb a little bit more of the radiation, and so what you’ll get is a much smaller dose,” Wellerstein says. Even if radiation levels are seriously high, you may reduce them by a factor of 10—so instead of increased risk of both cancer and radiation sickness, you may just slightly increase your cancer risk. Better!

Be prepared to leave and decide if you should

Now that you’re inside, in fresh clothes, and away from windows, you need to decide how long to stay and whether it’s a safe place to be.

If you receive an evacuation order from local authorities, you should pay attention to it, but know that such orders are sometimes issued prematurely, not at all, or too late. Since nuclear events are both rare and potentially catastrophic, as well as opaque and confusing, an incorrect response that triggers a mass panic could be worse than the actual event. “It’s really tricky for a government to figure out what to do,” Wellerstein says.

That leaves you with the responsibility of deciding whether to stay put or seek shelter elsewhere. Whether you choose to wait for an official evacuation order, or decide against it, remember you will still likely want to wait at least 72 hours after an event before you go outside again. That said, if you have reliable information that a radioactive plume is headed your way, you may wisely choose to grab your things and go.

Go shopping

Once the radioactive plume has passed, you should abandon that year’s garden. Don’t eat stuff that’s been outside, and if you had clothes drying on a clothesline at the time of the event, don’t wear them. It’s all likely to have been contaminated with radioactive material, so eating or wearing any of it would probably put a source of radiation directly on or in your body, raising the chance that you absorb a dangerous dose.

These are all viable options to protect yourself if the nuclear event is not too big and not a full-scale exchange of nuclear weapons. If the latter happens and you manage to survive the blast, society will most likely collapse and you’ll need a lifetime’s worth of DIY guides to rebuild civilization and survive in a post-apocalyptic hellscape.

Correction: A previous version of this article mistakenly implied taking potassium iodide pills in a nuclear event may protect your thyroid gland from absorbing too much radioactive potassium. Potassium iodide pills actually protect the thyroid from absorbing radioactive iodine. Also, the current version of this article includes a quote from the NRC.