Normal Accidents: Living with High-Risk Technologies is a 1984 book by Yale sociologist Charles Perrow, which provides a detailed analysis of complex systems conducted from a social sciences perspective. It was the first to "propose a framework for characterizing complex technological systems such as air traffic, marine traffic, chemical plants, dams, and especially nuclear power plants according to their riskiness". Perrow says that multiple and unexpected failures are built into society's complex and tightly-coupled systems. Such accidents are unavoidable and cannot be designed around.