Related to your question, the episode also explores the history of "duck and cover." It turns out it's there is some credibility to the technique. In September 1945, the US sent a team called the Atomic Bomb Casualty Commission to Japan to research and interview survivors of nuclear blasts. They located survivors just a few blocks from the explosion epicenter, who had been sheltered by concrete basements. They also heard stories of people who were killed just by shattering windows and falling debris. With just some ability to shelter, survivability might be higher than you suspect.