...and impact conditions at Battery Park and other venues. Prototype solutions include a roadway trench with compressible fill and a thin planting cover, which can be used in open landscaped areas without being obvious. When strategically located, the trench will stop cars and trucks from accelerating toward potential targets. "These public amenities merge security and urban design, without creating a fortress for commercial tenants, commuters and residents," says Stephanie Gelb, BPCA Vice President Planning and Design.

The multidisciplinary design team developing security solutions consists of Rogers Marvel Architects, Weidlin-ger Associates Inc. (structural and blast engineering), Ducibella Venter Santore (security), Langan Engineers, (civil, geo-technical), and Sam Schwartz Co. (traffic engineering). Traffic-calming devices that reduce vehicular speed and increase standoff or setback distance from commercial buildings include raised, textured cobblestone crosswalks, curb lines and curb cuts. Standoff criteria, including vehicular size, speed, velocity and traffic patterns, are critical at long, narrow streets near high-risk targets. Road access, street layouts, ramps, movable bollard placement, truck docks, turning areas and speed-resistant elements are other factors when reviewing perimeter security.

Owners, especially in urban areas, can protect buildings through a combination of standoff, redundancy, progressive collapse prevention and hardening of critical exterior elements that could be exposed to threats, say engineers. Performing a vulnerability analysis and incorporating protective design during early conceptual stages minimizes costs, especially for new buildings, says Richard Tomasetti, co-chairman of The Thornton-Tomasetti Group, New York City.

"The design threat is now a common part of the vocabulary," says Tomasetti. "Architects and engineers must understand how to address the design threat, along with sustainability, wind, gravity, seismic, dead loads, energy, mechanical, electrical and plumbing concerns."

When additional security is required, structural engineers use computer modeling to determine redundancy levels and minimize building renovations. Redundancy reduces local effect of damage to one part of a building. Hardening technology is appropriate when standoff and redundancy cannot be addressed, especially for existing buildings. Laminated glass and polymer film in window frames can reduce life safety risks by preventing flying glass shards from injuring building occupants.

As building security techniques are absorbed into the industry mainstream, design professionals and building owners must be aware of the potential liability risks that arise when security needs increase. The standard of care has changed since 9/11, beyond traditional concerns.

"Everyone must anticipate potential areas of liability that were not apparent in the past," says Raymond T. Mellon, partner of the New York City-based law firm Zetlin & De Chiara LLP. "The need for building hardening against blast is obvious now. But owners should anticipate ways to reduce the impact of a chemical biological attack, for example, by ensuring mechanical air intake vents are located above grade to prevent tamper-ing."

Design professionals can mitigate liability risks by documenting all efforts to make owners aware of potential threats and the recommended remedial measures and by shifting the burden for noncompliance onto the owner. Although owners may decide not to implement some or all of remedial measures, architects and engineers are obligated to alert their clients about possible design threats and solutions, Mellon says. Owners cannot be forced to pay for recommended security measures, but creating a paper trail will diminish further liability.