Over the past few decades, the number of skyscrapers worldwide has climbed dramatically. And as developers look to maximize limited urban space, and nations vie for prestige, these shimmering towers are being built higher and higher. In China alone, dozens of buildings rise to over 1,000 feet, with a few approaching 2,000 feet. But for all their impressive engineering, are these buildings safe? And are building regulations keeping up with the soaring heights of new structures? In San Francisco, skyscrapers can be built on unstable, sinking ground. And internal sprinkler systems are the only hope for extinguishing fires that burn beyond the reach of firefighters' ladders. Now, NOVA explores the science behind the risks of sky-high buildings, from the structural limits of building materials to the threats presented by wind, fire, and earthquakes. Experts show how the science of evacuation has shaped buildings in recent years, and what we have-and haven't-learned from past tragedies.