Several years ago, a New York City firefighter named Jason Charles read the novel “One Second After,” by William R. Forstchen, and decided to change his life. In the book, an electromagnetic pulse goes off and sends the United States back into the Dark Ages; in its foreword, Newt Gingrich writes that this technology is not only real but terrorists know about it. “It was pretty much a green light for me to start prepping,” Charles says. The latest episode of The New Yorker’s “Annals of Obsession” video series centers on doomsday preppers—people who aim to equip themselves with the skills and materials they would need to survive a world-ending calamity. Charles is now the organizer of the group N.Y.C. Preppers, which teaches city dwellers how to fend for themselves. He says that he has stockpiled enough supplies that, if the worst came to pass, he would be able to be self-reliant for a year and a half.