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).

    Allow some office workers to use elevators in an emergency. Conventionally, in an emergency situation, elevators in high-rise buildings are used by firefighters only. NIST recommends building elevators that can withstand fires and structural damage in the concrete core of a building.

    Mark stairwells and exits with glow-in-the-dark signs. As simple as it sounds, not every building has such markings, especially those built before the 2000s. New York was the first large city to require luminous markings in stairwells, five years after the 9/11 tragic events. More than 1,500 buildings now have the markings, but that’s still a small fraction of America’s tall buildings.

    If a city adopts these recommendations – and also asks tall buildings to include refuge floors, video-camera surveillance, and automatic sprinkler systems — the safety of the skyscrapers will increase significantly.

    Relaxing the requirements of a helipad also will empower architects to create more interesting rooftops. A space 50-by-50-feet wide at minimum is required for a helipad spot, plus a typical additional 25 feet around it as a buffer. This has resulted in a repetitive, boxy roof shape in the Los Angeles skyline.

    Beyond aesthetics, boxy rooftops with helipads are really a missed opportunity to create “green” roofs with sustainable features. Now Los Angeles can do something like the spiral form in the rooftop of Shanghai Tower in Shanghai that captures rainwater. Some towers’ tops are now designated for wind turbines to harness wind energy, such as the Strata Tower in London.

    There’s nothing to fear – and much to gain – in relaxing the helipad requirement. I, for one, will be watching to see what inventive skyscrapers Angelinos come up with.

    Kheir Al-Kodmany is a professor in the Department of Urban Planning and Policy at the University of Illinois at Chicago. He wrote this for Zocalo Public Square.

    允许部分上班族在紧急情况下使用电梯。按照惯例，在紧急情况下，高层建筑的电梯仅供消防人员使用。NIST建议，建筑电梯应能够承受火灾和混凝土芯结构受损。

    使用黑暗中可发光的标志指示楼梯间与紧急出口。听起来很简单，但并非所有建筑都有这样的标记，尤其是在2000年之前建造的建筑。911事件的悲剧发生5年后，纽约市规定在楼梯间设置发光标识，纽约因此成为第一个有类似规定的大城市。目前，超过1,500栋建筑设置了类似标志，但这在美国的高层建筑中仅占一小部分。

    如果一个城市采用了这些建议，并且要求高层建筑设置避难层、视频监控和自动洒水系统，摩天大楼的安全性将大幅提高。

    此外，放宽对直升机停机坪的要求，也可以使建筑师们设计出更有趣的屋顶天台。直升机停机坪至少需要50x50英尺的空间，而且周围通常要设立25英尺的缓冲区。这导致各种大同小异、四四方方的屋顶，占据了洛杉矶的天际线。

    除了有失美感外，设有直升机停机坪的四方屋顶，也错过了利用可持续功能创建“绿色”屋顶的机会。现在，洛杉矶的大楼也可以像上海的上海中心大厦（Shanghai Tower）一样，在屋顶设计可以收集雨水的螺旋形结构。部分摩天大楼的屋顶设计了风力涡轮机，用来风力发电，例如伦敦的斯特拉塔（Strata Tower）。

    对于放宽摩天大楼楼顶直升机停机坪的规定，我们无须担心，恰恰相反，这将给我们带来许多好处。洛杉矶人会设计出哪些有创意的摩天大楼呢？我很期待。

    本为作者海尔•阿尔孔德曼尼是伊利诺伊大学芝加哥分校（University of Illinois at Chicago）城市规划与政策系教授。本文原刊登于信息交流网站Zocalo Public Square。（财富中文网）

    译者：刘进龙/汪皓