The full scope of a nuclear detonation  is almost unimaginable. Hopefully, no one will ever experience  another of these catastrophic incidents. But there is a scientifically supported  plan of action that could save hundreds  of thousands of lives in the area surrounding  a nuclear explosion. So what is this plan, and what exactly would it protect us from? To create their destructive blast, these weapons harness  the power of nuclear fission– in which an atom’s nucleus  is split in two. This process produces an incredible  amount of energy, and in some materials the neutrons  produced by one fission are absorbed by nearby atoms, splitting additional nuclei. These chain reactions can produce  a range of explosive yields, but let’s consider an explosion  equivalent to 10,000 tons of TNT. An explosion like this would create a fireball capable of decimating  a few city blocks and a shockwave damaging buildings  several kilometers away. There is tragically nothing  that can be done to save those in the fireball’s radius. However, for those in the  shockwave and beyond, our scientifically supported protocol  could be life saving. And though it may sound surprising, the best way to stay protected before,  during, and after a nuclear detonation, is getting inside. Similar to protecting yourself  from tornadoes or hurricanes, getting and staying inside a sturdy  building would offer protection from the explosion’s shockwave,  heat, and radiation. The shockwave of energy would travel several kilometers beyond the fireball’s  radius in the first few seconds. Sturdy buildings within that range should be able to withstand the shockwave, and staying in the centers and basements  of these buildings also helps provide protection from  heat and flying objects. Finding shelter is especially important  if the fireball occurs close to the earth, as it will pull thousands of tons of dirt  and debris several kilometers into the atmosphere. As the fireball cools, unstable atoms created by the nuclear  fission mix with the debris to produce the most dangerous long-term  effect of a nuclear detonation: radioactive particles called fallout. These sand-sized particles emit  ionizing radiation, capable of separating electrons from  molecules and atoms. Exposure to massive amounts of this  radiation can result in cell damage, radiation burns, radiation sickness,  cancer, and even death. Created several kilometers up, dangerous concentrations of this material would be driven by upper  atmospheric winds, potentially leading to hazardous  levels of fallout in areas up to tens of  kilometers downwind. Thankfully, the same buildings that offer protection from the blast are even better at  guarding against fallout. Radiation is reduced as it travels  through space and mass. So while a broken window and sealed window both have the same minimal  effect on radiation, thick layers of steel, concrete,  and packed earth can offer serious protection. And since fallout gives off half of its  energy in the first hour and 80% in the first day, staying inside for 24 hours could  dramatically improve the odds of avoiding the most serious  effects of radiation. Following the blast there would be at  least 15 minutes to find shelter before the fallout begins. Since the most hazardous fallout particles are the heaviest, they sink through the air and collect on streets and rooftops, making ideal shelters underground  or in the middle of high-rise buildings. But if someone were to get  caught in the fallout, there are still measures they could take. After finding a safe space, they should remove their shoes  and outer layers, wash any exposed skin, and store the contaminated  clothing far away. Once inside, plan on staying there  for at least 24 hours. If the shelter is poor, or someone  inside needs urgent medical attention, try seeking outside help after an hour. But ideally, stay inside and stay tuned for more  information from first responders. While electric power, cell service, and Internet would be down, most radios would likely survive. So listen in for emergency responders to determine the safest course forward. Nuclear weapons are some of the most  powerful tools of destruction on Earth, and it may seem naive to put faith in these straightforward protective measures. But studies and simulations have  repeatedly shown the benefits of getting inside. So while we’ll hopefully never need to, remember to Get Inside, Stay Inside,  and Stay Tuned.