Hunker down or run? What to do after a nuclear detonation

Sheltering in place isn't always the best strategy, a new study shows. Sometimes you need to make a run for it.

Say it’s actually happened. A nuclear explosion in a major urban area. It’s Independence Day in real life, and the President didn’t think he had another option. You’re in a makeshift shelter (a cast-iron tub, maybe), and you know there’s a basement with thick concrete walls nearby. Radioactive fallout is on its way. Do you stay or do you go?

Science may have an answer. Michael Dillon from Lawrence Livermore National Laboratory has developed a model to minimize fallout radiation for people seeking safety.

During the Cold War, pretty much every imaginable outcome of a nuclear blast was modeled. But Dillon, ScienceNOW reports, found a gap in the sheltering strategies for people far enough from ground zero to survive the initial blast, but close enough to face deadly fallout.

So, focusing on a single low-yield nuclear detonation (like those used on Hiroshima and Nagasaki), Dillon figured out variables that matter for fallout survival, and did some calculus. ScienceNOW breaks it down
  • The longer you stay outside, the higher your radiation dose -- but the environmental radiation intensity also decreases over time. 
  • Your total dose is a function of when you step outside, your distance from the detonation, how long you run before you reach better shelter, and how much shielding you get from the local environment while you’re out there. 
  • The critical number is: the ratio of the time you spend hunkering down in your first shelter to the time you spend moving to the high-quality shelter
After working out various shelter options and transit times, Dillon found that sheltering in place isn’t always the best strategy. The answer to the above scenario is: 
  • If you’re in a poor-quality shelter -- and you know there’s an adequate shelter within 5 minutes away -- run to the better one immediately. 
  • If you’re in a poor-quality shelter -- and an adequate one is 15 minutes away -- you can stay where you are, but wait no more than 30 minutes after the detonation. Then run.

After those 30 minutes, the initial radiation from the explosion is long gone, iO9 explains, and your main danger is from the sand-sized particles that have fallen around you -- so brush those off. Dillon says he would wait about 12 to 24 hours before going outside again afterwards. 

This proposal could save between 10,000 and 100,000 people from fatal exposure to fallout radiation, Dillon argues. The model could help emergency planners develop response strategies and evacuation plans. Current U.S. government guidelines can be found here.

Obviously there are plenty of “but what ifs.” To simplify the calculation, Dillon had to make assumptions about shelter capacities and basic human behavior in the aftermath of a disaster.

The work was published in Proceedings of the Royal Society A last week. 

Image: Steve Snodgrass via Flickr

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