For 40 years, Los Angeles’ building code has required all buildings 75 feet and taller to have a rooftop emergency helicopter landing facility in a location approved by the fire chief. The idea in 1974, when the law was passed, was to make skyscrapers safer, in part as a reaction to a catastrophic fire in Brazil. But we know now there are better ways to make structures like the landmark U.S. Bank tower safe. I, for one, am cheering for the recently announced end of a policy requiring flat-topped buildings in Los Angeles. It’s a policy that holds lessons for tall buildings everywhere.

    As an urban planner and architect (before becoming a professor, I was an architect at SOM-Chicago, the former Skidmore, Owings & Merrill), I know safety is more critical in tall buildings than in low-rise structures because tall buildings host a greater number of inhabitants and are themselves expensive investments. I also know that, if appropriately designed and built, skyscrapers are safer in many respects than low-rise and mid-rise buildings. They have concrete cores that are designed to withstand the extreme lateral forces and loads that occur during high winds and earthquakes. Fire safety systems in skyscrapers include sprinklers and wet and dry standpipes, to which firefighting hoses can be connected.

    Codes for tall building safety were found to be deficient following the World Trade Center collapse in 2001. The National Institute of Standards and Technology concluded it would have taken more than three hours to evacuate the buildings if they had been full of people at the time of the attacks. In the process, 14,000 people – 28% of the occupants – would have died because of insufficient stairwell capacity.

    NIST stressed that time is of the essence in evacuation. And helipads have a very small impact on evacuation times. Helicopters take time to land, load people, and take off. They only take a small number of a skyscraper’s occupants each time. Research indicated that if the World Trade Center rooftops had been accessible (the helipad fell in disuse), helicopters couldn’t have landed because of the heat and smoke.

    Our rarely used helipads may enhance the perception of safety but do little else. The NIST study called for a smarter strategy of using building design for safety. Among the key elements:

    Assume that the full building will evacuate. Conventionally, builders of high-rises have assumed “staged evacuations” will occur. During a fire on one floor, occupants were supposed to evacuate to adjacent floors until it was safe to return. After the World Trade Center collapse, it became clear a tall building’s occupants would likely want to evacuate all at once in an emergency situation. NIST recommends that all non-residential skyscrapers that exceed 420 feet in height have three stairwells and fireproofing capable of withstanding a pressure of 1,000 pounds per square foot (in the event of a bomb, gas breakout, or something similar).