In the wake of the Oklahoma City bombing in 1995 , the government classified all buildings into five security levels and established minimum security requirements for them . These buildings contain mission functions critical to national security , such as the Pentagon or CIA Headquarters . A Level-V building should be similar to a Level-IV building in terms of number of employees and square footage . It should have at least the security features of a Level-IV building . The missions of Level-V buildings require that tenant agencies secure the site according to their own requirements
Oklahoma City bombing
Oklahoma City bombing
United States federal building security