Design basis accident is a big fancy term that describes the worst thing that could happen in a building or facility. It's like when mom and dad tell you to be careful when you play with matches because you don't want to start a fire.
When scientists and engineers build something like a power plant or a chemical factory, they have to think about what could go wrong and make plans to prevent it. They create a safety plan for the worst possible accidents or disasters that could happen. They call this safety plan the design basis accident.
Think of it like a secret plan in case something bad happens. But it's not really a secret – everyone who works in the building or facility knows about it, and they practice what to do in case of an emergency.
The design basis accident includes things like earthquakes, fires, explosions, or leaks of dangerous chemicals. It's important to have a plan for these things so that everyone can stay safe and know just what to do if they happen. It's like having a map to help you find your way if you get lost.
So, design basis accident is just a fancy way of saying that smart people think about all the things that could go wrong and make a plan to keep people safe.