THE MAGAZINE

The Challenge of Making Safer Structures

By Michael A. Gips

Slow going.
Despite a lot of talk by city building officials, architects, engineers, and security professionals, few cities have amended their building or life-safety codes as a direct consequence of 9-11.

The process of gathering and analyzing data from which code changes can be made is going "extremely slowly, unnecessarily slowly," says W. Gene Corley, an engineer who headed a building-performance study of the WTC collapse conducted by the Federal Emergency Management Agency (FEMA). The findings of that study were published in May 2002.

"There doesn't seem to be a sense of urgency," says Corley, who also helped analyze the remains of the Oklahoma City Murrah Federal building after its 1995 bombing.

Part of the problem, says Shuki Einstein, lead project architect for CH2M Hill, a global engineering and construction-management firm, is that there's no real pressure for building codes to change. Insurance companies might eventually alter that situation, he says, if they threaten to impose higher premiums on companies owning or occupying buildings that do not meet recommended criteria. "Then maybe building code standards will go up," Einstein surmises.

Absent code changes or economic incentives, builders and developers are understandably reluctant to make costly upgrades. Building developers certainly won't drive a trend toward better practices, says Einstein. "Developers are going to do the minimum to meet the building code."

Not everyone believes code changes are necessary. In a paper written for the American Institute of Steel Construction Inc., Nester Iwankiw and Lawrence G. Griffis advocate studying the behavior of buildings under abnormal loads, to create not code but a design tool. Sweeping code changes, rather than voluntary improvements dictated by individual risk assessments, might be an "overreaction," they write.

Ground Zero.
That go-slow attitude is not universal, however. As the epicenter of the 9-11 attacks, New York City was profoundly affected, and it has taken the lessons to heart.

As a result, developers there have been proactive. For example, Silverstein Properties, which owns the World Trade Center site, "is very interested in going well beyond building codes," says Carl Galioto, a partner at the architecture, engineering, and urban-design firm Skidmore, Owings & Merrill. "They've been an active leader and partner in developing new ideas," says Galioto, who is also a member of the New York building code commission.

Consider the new Seven WTC building. It was designed with a "robust structure" to protect against progressive collapse, Galioto says. (See "Pondering the Meaning of 'Progressive Collapse,' " below.) This measure addresses the fact that fires in the Twin Towers damaged vertical support members, leading to the buildings' collapse.

In addition, stairs and elevators are fully encased in a reinforced concrete core. This reflects FEMA's finding that the plasterboard that was providing fire resistance to the stairways at the Twin Towers was knocked off by the impact of the jets, rendering it useless and possibly hastening the buildings' collapse.

Seven WTC also has spray-on fireproofing five times more adhesive than called for by existing standards, says Galioto. It has a redundant water supply for sprinkler systems as well.

Another fire-safety feature in Seven WTC is that fire stairs are located at opposite ends of the building. (The FEMA report noted that the suicide pilots on 9-11 were able to slice through two sets of emergency stairs because the stairs were close together.) And at 66 inches, stair width goes well beyond code.

Voluntary widening of fire stairs in other buildings is an item under discussion by experts, not just to help with evacuation but to allow space for the counterflow of emergency responders. Many building owners may, however, balk at widening stairs, says architect Barbara Nadel, author of the book Building Security: Handbook for Architectural Planning and Design, because it reduces rentable space.

Moreover, Seven WTC and Freedom Plaza across the street have photoluminescent paint or electroluminescent strips on exit stairs even though they are not yet mandated by code. Freedom Tower will have a third stairwell dedicated to emergency response. And the stairwells in Seven WTC have triple redundancy for stair lights: First, there is emergency lighting to back up regular lighting; then there is battery power; and, if those fail, the photoluminescent paint is in place.

Galioto's firm is also studying how and whether it could implement some type of stair pressurization to reduce smoke in the stairwells in the event of an emergency. Higher air-pressure levels inside stairwells than exists on the floors reduces smoke migration through closed doors, he explains.

Such measures are feasible at the WTC site, but are they cost-effective for other properties? According to Galioto, the overall cost of extra security at Freedom Tower and Seven WTC "will be in the single-digit percentages of construction costs," not including the dedicated emergency stairwell and the wider stairs. These buildings can serve as an example for other iconic or high-risk buildings beyond Ground Zero, he says.

Code. While firms like Galioto's have voluntarily incorporated new life-safety features into their building designs at Ground Zero, the city of New York did not want to rely solely on the goodwill of private industry.

To that end, New York City's Department of Buildings formed its own building code task force, which gathered input from government agencies, design and engineering societies, the construction industry, real estate associations, and other experts. The task force also considered earlier recommendations from FEMA, but it preferred not to wait for this year's NIST report before taking action.

In February 2003, the task force issued 21 recommendations. For example, the task force proposed a requirement that new commercial high rises have elevators that open onto a "smoke-stop vestibule."

In addition, it suggested that existing buildings be required to have inspections, when spaces are being renovated, to assess existing spray-on fireproofing. The task force further recommended that nonresidential high rises be barred from using open-web steel joists. These structural members, which support floors and ceilings, have too little surface area for adequate spray-on fireproofing to be applied.

These proposals echoed the earlier FEMA report findings about the adequacy of fireproofing at WTC buildings. The FEMA building analysis of the WTC remains had found, for example, that some important structural members in the towers lacked adequate--or any--fireproofing.

New York City has codified most of these recommendations through a local law that came into effect in June 2004. As these new codes are implemented, they may serve as a testing ground and a model for other localities.

Four of the provisions apply retroactively to existing buildings but allow considerable time for compliance. For example, office buildings that are 100-feet tall or higher must have adequate sprinkler systems throughout the premises, but building owners have until July 1, 2019, to comply.

For installation of photoluminescent markings on exit signs and stairs, however, high rises have only until July 1, 2006. They have a year beyond that to install additional signs where the exit path is not clear and to provide a battery or generator as a backup power source for existing illuminated exit signs.

The changes are lauded by fire-safety experts, though some criticize the lengthy time allotted for compliance. One positive step, according to Vincent Dunn, a high-rise fire-safety expert and former New York City fire chief, is a provision requiring stair and elevator enclosures to be constructed of "impact-resistant materials."

At the same time, he notes that few of the new rules apply to existing buildings. "There are thousands of existing high rises," he says. "What happens to them?"

He points out that many New York high rises lacking sprinklers have open floor designs with 10,000 to 20,000 square feet of open space. A single fire hose can only handle 2,500 square feet, he says. "It's very hard to extinguish these fires."

Chicago. New York City has not been the only municipality to take seriously the need for changes after 9-11. Changes to Chicago's municipal code, reflecting more stringent high-rise-safety requirements, quickly followed 9-11. But the Chicago Department of Buildings code changes focused more on planning and the human factor than on structural building issues.

The Chicago provisions tie fire-safety measures to building height. For example, all office buildings 80-feet tall or more must have an emergency evacuation plan in place, but only those 540 feet or higher must file the plan with the city's office of emergency communications.

The tallest buildings, those more than 780 feet, must designate a fire-safety director, deputy fire-safety directors, a building-evacuation supervisor, fire wardens, and an emergency-evacuation team. Slightly shorter buildings, over 540 feet and up to 780 feet, need not have fire wardens. Buildings between 275 feet and 540 feet need only designate a fire-safety director and deputies.

The provisions include specific staffing requirements; a building's fire-safety directors or deputies, for example, must be on site when more than half of the building's regular occupants are present.

Other elements of a valid evacuation plan include evacuation procedures, the posting of a core floor plan, maintenance of a list of occupants needing evacuation assistance, and regular staff participation in safety drills. Stairwells must also be marked to identify floor number and the site of re-entry locations.

Not all of the Chicago code changes are personnel related, however, and some are driven by events other than 9-11. For example, an ordinance passed after the October 2003 fire at the Cook County Administration Building, which killed six people, prohibits the locking of reentry doors in stairwells. And just days after a December 2004 high-rise fire, the city council voted to make owners of pre-1975 commercial high rises install sprinkler systems (a 1975 provision requires only new buildings to have sprinklers). But the impact of that change is blunted by a 12-year grace period for compliance.

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