The 9/11 attacks "challenged perceptions of safety and security in the living and working environment and prompted questions about the viability of tall buildings," says David Scott, chairman of the Council on Tall Buildings and Urban Habitat.
"Tall building design moved out of the technical domain and into the public domain. Though it is neither practical nor feasible to design buildings to withstand every forseeable extreme event, safety concerns have led building owners, developers and occupants to demand more robust building designs, and that demand has been answered," Scott says
Among questions raised in the wake of the collapse of the World Trade Center:
·What are the life safety and insurance issues associated with extreme events?
·What is the best way to measure how buildings actually perform in fires and other catastrophic events?
·What tools are available to satisfactorily resolve the issues and alleviate concerns?
·Can similar disasters occur again, even without extreme causes?
Since 2001, numerous bodies throughout the world, including the National Institute of Standards and Technology (NIST), have reviewed these concerns and identified critical issues that form the basis of improved safety guidelines for new tall building design. These include:
·Building evacuation. There has been a move away from the traditional approach of relocation and defend in-place (only 1-3 floors evacuate in a fire), with greater emphasis on providing facilities and management techniques to allow safe phased total evacuation. Accommodating evacuation of mobility-impaired occupants has been essential in these new designs.
·Elevators. Use of elevators in non-fire events is increasingly factored into the design via specially-created protected shafts, power supplies and controls to provide a robust response in an extreme event. Elevators significantly improve evacuation times.
·Structural stability. Designing building structures to better withstand severe fire or other events with the goal of preventing progressive or disproportionate collapse. Specific attention is given to multi-story fires, aircraft impacts or blasts. The role of structural connections and their importance in maintaining structural stability is a prime focus.
·Materials. Detailing robust fire protection materials that can withstand impact and other external influences.
·Emergency access. Providing dedicated firefighting access, such as internal stair cores and elevators for exclusive use by emergency responders, to facilitate access and reduce possibility of interfering with escaping occupants.
·Communication. Improved communication devices and facilities for firefighters to allow swift response and emergency planning.
·Building management. Development of strategies that contemplate a range of potential catastrophic events, with adequate communication facilities and knowledge to enable prompt response.
Not every building requires the same level of safety and security measures. Building-specific emergency protocols should be based on occupancy levels, location, height, use, and level of threat. Threat and risk assessment can provide a suitable framework for developing a robust, cost-effective design solution.
These new approaches and heightened awareness will help prevent future catastrophic building collapse and have helped to rebuild confidence in high-rise buildings, Scott says.
