North Korea's consistent nuclear bravado over the last few months has given American emergency response planners reason to prepare the public for a possible nuclear attack, NBC News reported in April.
Their simplest warning is this: "Don’t run. Get inside." The best shelter would offer layers of protection, like dirt, walls and concrete, to prevent direct exposure to radiation that comes after a nuclear blast.
There's federally sanctioned nuclear safety directives available at Ready.gov, though they have not been widely shared. The FEMA and Department of Homeland Security-run site recommends staying inside for at least a day, unless authorities advise otherwise.
Local officials in Southern California have already been campaigning to be ready for a nuclear attack since 2013, offering an 18-page educational pamphlet, four videos and a school curriculum, all with the message, "Get inside, stay inside, stay tuned," according to the public health medical director who led the effort.