Safety is a controversial term. Whether it's radiation in rainwater, or radiation itself, getting everyone to agree on a definition of safe is very, very difficult. Even for engineers. Why? Mainly, because "it's a societal term," explains engineer Henry Petroski.
NPR explores how "safety" is easily influenced and shifted around, by forces both educated and otherwise. And because the possibilites of what can go wrong are infinite, nothing will ever be completely safe—that's why nuclear plants have to plan for meteor strikes. But safety is also subject to our shaky psychology—and we tend to err towards the comforting: "We don't see what we don't want to see. We don't want to think about scary things," Yotaro Hatamura, an emeritus professor of engineering at the University of Tokyo, explains. "That's just human nature." [NPR]