Stainless steel has earned its reputation as one of the most corrosion-resistant materials in engineering. But when used in the wrong environment, that reputation can be dangerously misleading. This is exactly what happened in 1985, when the roof of a swimming pool in Uster, Switzerland collapsed without warning, killing 12 people and injuring many others. In this video, we explore the science behind stainless steels - what they are, how they achieve their remarkable corrosion resistance, and the unexpected failure mechanisms that can turn a trusted material into a critical point of failure.