A U.S. Air Force base in Texas has taken the first steps to guard against an electromagnetic pulse (EMP) attack. But what, exactly, is an EMP, and how big is the threat? Officials at the Joint Base San Antonio in Lackland, Texas, issued a request for bids to carry out a survey of a facility called the Petroleum, Oil and Lubrication Complex. The survey will identify any equipment that could be vulnerable to an EMP ahead of more detailed… – Live Science Photo:Arbyreed