This series of publications was developed in response to the September 11, 2001 terrorist attacks on the New York World Trade Center and the subsequent events that led to the formation of DHS and an increased emphasis on preparedness and mitigation of terrorism-related hazards. One issue that FEMA began shortly after that was to examine whether lessons learned in response to natural hazards could be effectively applied to protect building occupants from human threats. Important similarities between seismic and blast loadings (e.g., both can impose extreme horizontal forces on a structure within a small time frame) lend themselves to such examination.