Cooling the water presented another challenge for SOM's engineers. "When we first started coming to Dubai, we noticed that the hot water in our hotels was very hot, and that the cold water was also very hot," says Leung. "Imagine getting hot water out of the cold faucet at the Armani Hotel!"

Since Dubai has limited fresh water and relies on the sea, the water had to travel through the very hot ground during the salt evaporation process. Instead of following that scenario, SOM took advantage of the area's high humidity and the large amount of condensation that results. "The moisture is so high that if you collect condensate in the air during a cooling period, you get a significant amount of water in the 55-65 degree Fahrenheit range," explains Leung. This water is collected and drained in a separate piping system to a holding tank. The system provides about 15 million gallons of supplemental water per year. A sitewide graywater collection system collects water for use in landscape irrigation.

The effects of air pressure are more noticeable to the average visitor to the Burj. There is an enormous amount of air movement going through the building. Due to Dubai's high temperatures, reaching 115 degrees Fahrenheit and higher in the summers, the stack effect is reversed. Instead of hot air rising, it is sucked in from the top of the building and directed downward because the inside of the building is cooler than the outside.

Stack effect is a function of both the building's height and the temperature difference between the inside and the outside. Both are extreme in this case. When you enter the building in the heat of summer, the air will feel like it is trying to push you out. "In Chicago, for instance, it is 75 degrees inside and as high as 95 degrees outside on a summer day," Leung explains. "In Dubai, the temperature difference in summer can be more than 40 degrees Fahrenheit."

What is not so apparent from the building's height is the amount of power it consumes. As electricity travels through the building, which in essence is a stack of five 30-story buildings, it loses voltage similar to the way water loses pressure flowing through a small pipe. To supply these massive loads efficiently, the Burj's electrical mains are supplied with 11 kV, 23 times higher than the 480V typically used in the U.S. Transformers located at each of the mechanical levels reduce the voltage to intermediate levels for heavy equipment and to 220V, the normal voltage used in the U.A.E., for office equipment and appliances.

Fire-and life-safety issues are a vital concern in high-rise buildings, particularly one of unprecedented height such as this. The Burj contains 57 elevators, some of the fastest in the world, serving different building zones, though no one elevator travels more than 500 meters (1,640 feet). According to Baker, the longest elevator ride takes under two minutes - with the express elevator to the observation deck on level 124 taking much less time. Baker also admits to walking down the full height of the building (at a leisurely pace) in about 45 minutes. A typical floor contains three sets of concrete-encased fire stairs, one in each wing.

In case of fire emergency, the building deploys a "defend in place" strategy. Fire-rated, air- conditioned refuge areas accommodate building occupants until further instruction. Some elevators are equipped with cameras so that elevator shafts can be inspected remotely.

Despite the challenges involved in designing the Burj Khalifa, and the criticisms leveled against it in the wake of Dubai's subsequent financial meltdown, Adrian Smith staunchly defends it. "The Burj was an important piece for Dubai at the time it was built," says Smith. "Dubai wanted to be recognized as an international player on par with other major world cities, and it needed an international landmark to do that."