現代科技如何讓摩天大樓更安全

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.

40年來，洛杉磯的建築條例一直要求，所有75英尺以上的建築，要在消防部門批准的位置設置緊急直升機降落設施。1974年通過該法律的目的，是讓摩天大樓更安全，這在很大程度上是受到了巴西一場慘重火災的影響。但我們都知道，其實有許多更好的方法，可以讓美國銀行（U.S. Bank）大廈這樣的地標性建築更安全。最近，洛杉磯宣佈終止這項要求摩天大樓必須設計爲平頂的政策，我對此決定表示歡迎。這項政策對各地的高層建築有相當大的借鑑意義。

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.

作爲一名城市規劃師和建築師【成爲教授之前，筆者曾在SOM-Chicago建築事務所（原Skidmore, Owings & Merrill建築事務所）擔任建築師】，我很清楚，相比低層建築，安全性對於高層建築來說更加重要，因爲高層建築有更多居住者，而且高層建築本身的造價也更加不菲。此外，我也很清楚，如果經過合理的設計和建造，摩天大樓在某些方面比中低層建築更安全。摩天大樓的混凝土芯，可以承受強風和地震時的極端側向力和橫向載荷。摩天大樓的防火安全設施包括灑水裝置，以及可以直接連接消防軟管的溼式和乾式豎管。

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.

2001年世貿中心大廈倒塌之後，人們發現了高層建築安全規定的不足。美國國家標準與技術研究所（NIST）得出的結論是，如果大樓擠滿人的情況下遭遇襲擊，全部疏散需要三個多小時。在這個過程中，14,000人，即全部居住者的28%，會因爲樓梯間容量不足而喪生。

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.

NIST強調，時間是疏散的關鍵。而樓宇停機坪對疏散時間的影響微乎其微。直升機降落、登機和起飛都需要時間。而且，直升機每次僅能運送極少數摩天大樓居住者。研究顯示，由於大火產生的熱量和濃煙，即便直升機可以接近世貿中心大廈的屋頂（樓宇停機坪已被停用），也無法降落。

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:

極少被用到的直升機停機坪，可能會增強人們的安全感，除此之外毫無用處。NIST的研究呼籲更明智地使用建築設計實現安全性。這些設計要素包括：

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).

假設整棟建築都需要疏散。按照慣例，高層建築的建造者會假設將發生“分階段疏散”。當一層發生火災時，居住者在可以安全返回之前，應該先疏散到臨近樓層。世貿中心大廈倒塌證明，在緊急情況下，高層建築的居住者更希望全部疏散。NIST建議，所有高度超過420英尺的非居住用摩天大樓，應該設置三個電梯間，且耐火材料應該能夠承受每平方英尺1,000磅的壓力（發生炸彈襲擊、煤氣泄漏或其他類似事件時）。

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.

允許部分上班族在緊急情況下使用電梯。按照慣例，在緊急情況下，高層建築的電梯僅供消防人員使用。NIST建議，建築電梯應能夠承受火災和混凝土芯結構受損。

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.

使用黑暗中可發光的標誌指示樓梯間與緊急出口。聽起來很簡單，但並非所有建築都有這樣的標記，尤其是在2000年之前建造的建築。911事件的悲劇發生5年後，紐約市規定在樓梯間設置發光標識，紐約因此成爲第一個有類似規定的大城市。目前，超過1,500棟建築設置了類似標誌，但這在美國的高層建築中僅佔一小部分。

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.

如果一個城市採用了這些建議，並且要求高層建築設置避難層、視頻監控和自動灑水系統，摩天大樓的安全性將大幅提高。

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.

此外，放寬對直升機停機坪的要求，也可以使建築師們設計出更有趣的屋頂天台。直升機停機坪至少需要50x50英尺的空間，而且周圍通常要設立25英尺的緩衝區。這導致各種大同小異、四四方方的屋頂，佔據了洛杉磯的天際線。

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.

除了有失美感外，設有直升機停機坪的四方屋頂，也錯過了利用可持續功能創建“綠色”屋頂的機會。現在，洛杉磯的大樓也可以像上海的上海中心大廈（Shanghai Tower）一樣，在屋頂設計可以收集雨水的螺旋形結構。部分摩天大樓的屋頂設計了風力渦輪機，用來風力發電，例如倫敦的斯特拉塔（Strata Tower）。

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.

對於放寬摩天大樓樓頂直升機停機坪的規定，我們無須擔心，恰恰相反，這將給我們帶來許多好處。洛杉磯人會設計出哪些有創意的摩天大樓呢？我很期待。

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.

本爲作者海爾o阿爾孔德曼尼是伊利諾伊大學芝加哥分校（University of Illinois at Chicago）城市規劃與政策系教授。本文原刊登於信息交流網站Zocalo Public Square。