Public buildings typically seek to achieve many goals that include security/safety, sustainability, productivity, accessibility, functionality, aesthetics and cost-effectiveness. It is important to balance these goals depending upon the specific use and location of each public facility. For an overview of safety/security issues, you can download a copy of UNIFIED FACILITIES CRITERIA (UFC) DoD MINIMUM ANTITERRORISM STANDARDS FOR BUILDINGS at http://www.tisp.org/files/pdf/dodstandards.pdf .
Other documents (there are many more than this) to look at include:
Department of Health and Human Services' Guidance for Protecting Building Environments from Airborne Chemical, Biological, or Radiological Attacks, May 2002.
FEMA's Publication No. 386-7 Integrating Human-Caused Hazards into Mitigation Planning, Sep 2002.
FEMA's Publication No. 426 Reference Manual To Mitigate Potential Terrorist Attacks in High Occupancy Buildings, May 2003.
FEMA's Publication No. 427 Primer for Design of New Buildings to Mitigate Terrorist Acts, May 2003.
Approaches vary dramatically from facility to facility. Also note that political will plays an important role in this process.