PEC engineers are experienced in using the Vulnerability Assessment and Protection Option (VAPO) software developed by the Defense Threat Reduction Agency (DTRA) in design of blast resistant facilities and assessment of existing structures. VAPO is able to account for special features on buildings, such as reentrant corners and overhangs, by considering a three-dimensional model of the building, potential threats, and terrain elements. PEC engineers regularly use VAPO to develop an advanced understanding of the three-dimensional blast environment resulting from potential threats. Refined building models which account for the structural properties of envelope elements can also be used to calculate accurately and quickly the extents of building damage caused by threats. PEC has used VAPO in the design and assessment of multiple GSA facilities to provide the best level of analysis for these important sites.