Introduction

Mankind has always sought to eliminate unwanted risks to health and safety, or at least to bring them under control. Its successes are impressive, as evidenced by advances such as the discovery of vaccines that prevent polio and smallpox and the development of building methods that enable stadiums and skyscrapers to withstand powerful earthquakes. Despite our best efforts, however, some familiar risks persist while others that are less familiar are found to have escaped our attention far too long and new ones continue to arise.