How to survive an atomic bomb

The Associated Press reports something that anyone with a passing familiarity with nuclear weapons already knows:

D.C. Nuclear Blast Wouldn’t Destroy City, Report Says This is what the U.S. government imagines would happen if terrorists set off a nuclear bomb just blocks away from the White House: The explosion would destroy everything in every direction within one-half mile. An intense flash would blind drivers on the Beltway miles away. A radioactive cloud would drift toward Baltimore. But the surprising conclusion? Just a bit farther from the epicenter of the blast, such a nuclear explosion would be pretty survivable… “Few, if any, above ground buildings are expected to remain structurally sound or even standing, and few people would survive,” [the report] predicted. It described the blast area as a “no-go zone” for days afterward due to radiation. But the U.S. Capitol, the Supreme Court, the Washington Monument, the Lincoln and Jefferson memorials, and the Pentagon across the Potomac River were all in areas described as “light damage,” with some broken windows and mostly minor injuries.

This isn’t to say that such a blast would be a walk in the park — it would likely kill tens of thousands of people, and injure up to hundreds of thousands more — but it would not wipe Washington off of the map.

This conclusion may seem counter-intuitive, because when most of us think of nuclear weapons we think of the weapons the US and USSR built to aim at each other during the Cold War. But it’s important to understand that the type of bomb a terrorist group would be able to develop and deploy would be something very different — something very much smaller, and much less destructive.

How much less? The hypothetical terrorist bomb described in the report would explode with the force of 10,000 tons (or 10 kilotons) of TNT. Which is a lot, without question — but for comparison, consider that a single Minuteman III nuclear missile can carry a warhead rated to produce a blast of 350-475 kilotons of TNT. A 10-kiloton weapon isn’t even as powerful as the “Little Boy” bomb dropped on Hiroshima on August 6, 1945, which produced a yield somewhere between 15 and 20 kilotons. And that weapon, 50 to 100% more powerful as the one we’re discussing, didn’t destroy Hiroshima; it did enormous damage, to be sure, but the city survived and recovered.

The other thing to remember about a scenario like this is that it’s only one bomb. This is a key difference between this type of attack and what most people think of when they hear “nuclear weapons.” The image most people have of nuclear war is the Cold War scenario of the two great superpowers hurling tens of thousands of nukes at each other all at once — what RAND Corporation nuclear strategist Herman Kahn memorably described as a “wargasm.” It is this type of massive overkill attack that led to the concept that “the survivors would envy the dead,” since all they would be left with would be a world burnt to ashes, with all existing civilizations destroyed and no resources available to rebuild them.

The aftermath of a terrorist bomb would not be anything like that. Much of downtown D.C. would be in ruins, but most emergency services from Virginia and Maryland would still be intact and able to respond, and the rest of the nation (and the world) would be untouched and able to extend support. If you experienced an act of nuclear terrorism and survived, in other words, you would not be condemned to spending the rest of your life as an extra in a Mad Max movie. (Yes, life in Washington would never be the same after such an event, but “Washington’s economy would never fully recover” is still a long chalk from “the end of civilization as we know it.”)

Which brings me to the most important point about this type of scenario: it can be survived. It’s not like the Cold War wargasm scenario, where so much explosive tonnage is falling on your head that protecting yourself is impossible. There are things you can do if you find yourself in such a situation that can dramatically improve your chances of making it out alive.

The first thing to understand is that if you are still alive five minutes after a small nuclear weapon detonates, you are already very likely to continue surviving. People in the immediate vicinity of the explosion would be killed instantly, but because of the low yield of the bomb that vicinity is fairly localized; the study puts this area as about half a mile to a mile in radius.

If you happen to be in that area, there’s not a lot you can do to protect yourself. But if you’re there and you are still standing five minutes after the blast, or if you’re farther away when the bomb goes off, you’ve made it through the worst.

Assuming that you’re not killed instantly, then, the next thing to understand is that the decisions you make in the ten minutes after the bomb explodes will probably determine whether you live or die.

If you’re outside that immediate area but in the general region of the blast when it happens, your greatest initial risk will come from a direction you’re probably not expecting: your windows. A nuclear explosion begins with a dazzling flash; because light travels faster than sound (and everything else), this flash can precede the arrival of the blast from the explosion by 30 seconds or more. A great risk, therefore, is that people will see the flash in their peripheral vision, go to the window to see what happened, and then get lacerated by shards of flying glass as the blast wave arrives and shatters the window. So the first thing to know is that if you see “a bright flash of light like the sun, where the sun isn’t,” you should resist the temptation to investigate and instead take cover.

After the blast wave passes, if you’re still alive and ambulatory, your next decision will be whether to stay where you are or leave. Most people at this point will understandably feel the urge to flee the area at once. In most cases, though, this is exactly the wrong thing to do. The reason is simple: fallout.

When an atomic bomb explodes, the blast digs a big batch of dirt out of the ground and sends it flying up in the air. Because it’s been exposed to intense radiation, this dirt is highly radioactive. The force of the explosion sends it flying, but afterwards it begins to fall back to earth, carried along on its way down by the wind. This deadly dirt is nuclear fallout.

Unlike the bomb blast, radiation from fallout is only deadly if you’re exposed to it. So your immediate priority after surviving the initial blast should be to seek shelter immediately. You don’t have to touch the fallout directly to be exposed to its radiation; radiation can pass through solid materials, but it diffuses as it does so, so the more stuff (earth, concrete, brick, etc.) you can put between yourself and the fallout, the lower the amount of radiation that will be able to seep through to you.

Which means that what you want to do is find the place with the most stuff you can put between you and the radiation in the ten minutes or so you’ll have before the fallout starts to fall down on you. The ideal shelter from fallout is an underground concrete structure, because then you get protection not just from the walls but also from the earth around them and the building above them; but even the concrete walls of a modern above-ground office building can provide sufficient protection, especially if you take shelter in an interior room rather than one touching an exterior wall. You can see the “protection factor” (PF) of various types of shelter in the illustrations from the report over there on the right; note that the study puts the minimum acceptable PF for an “adequate” shelter at 10.

Odds are that your shelter isn’t someplace you’d be able to live comfortably in for a long period of time. But that’s completely OK! The point of this shelter isn’t to live in for a long period; it’s just to keep you away from the fallout while it’s highly radioactive. The intense radioactivity of fallout burns itself out surprisingly quickly; an hour after it falls it’s only half as radioactive as it originally was, and after a day it can be down to 20% or less. So your goal is to avoid exposure to radiation until the most intense radioactivity has subsided. (This is why fleeing immediately is such a bad idea; it puts you out in the open, completely unshielded from radiation, right at the time when the radioactivity is at its highest, most intense levels.)

How long you should stay in your shelter depends on how well-protected it is, because you’re trading off guaranteed but lower exposure in your shelter to more intense but less guaranteed exposure as you move farther from the blast area. (In other words, the farther away you get, the less likely you are to be exposed to radiation at all; but if you are exposed while on foot, you’re completely exposed. Whereas in your shelter you’re definitely going to get some exposure, but how much will depend on the protection the shelter offers.) If you’re in a sturdy underground concrete structure, you can stay there safely for as long as a day; if you’re huddling in an abandoned car, you should get moving immediately after the cloud of fallout passes. But in either case, sheltering in place during the initial period of highest radioactivity will dramatically increase your chances of survival.

Why am I going into these details? Because it ties in with one of my recurring themes here on this blog: that you should be prepared. In an emergency, the difference between life and death is frequently as simple as whether you keep your wits about you and take a few simple steps to protect yourself.

An act of nuclear terrorism would be a tragedy beyond anything in living memory, but it wouldn’t be the end of the world. And if you’re armed with a little knowledge, you can drive the odds that it would be the end of your world way down, too.

UPDATE (March 31): I meant to link to the original report when writing this so you could refer to it for more information, but somehow forgot to insert the actual link. Sorry about that! There’s two documents you should look at — this one from 2009 discussing the general risks, and this one from 2011 that looks at the Washington, DC scenario in more detail.

There’s also a lively discussion of this post happening on Reddit.