On a particularly cold, sunny day recently, thousands of people arriving in Lower Manhattan were forced to reroute their commute—because huge slivers of ice were cracking off of the One World Trade Center and plunging hundreds of feet down onto the street. And the WTC isn't alone.
Last year, Tokyo's new, 1,900-foot Sky Tree Tower had to be retrofitted with surface heaters to stop the deluge. In Chicago, the appearance of yellow warning signs are a yearly event. The dangers of falling ice are about as old as falling ice itself—but the way we design our tall buildings has something to do with it, too.
In fact, they might even be increasing it.
It turns out that a number of human factors are probably contributing to the increase in the ice shenanigans. For one thing, there are the high-performance glasses and claddings that architects specify to bring down a building's carbon footprint. By keeping heat inside—and the facade extremely cold—these high-tech materials facilitate ice formation on the outside of the building.
Photo by Win McNamee/Getty Images
Another issue is the sheer height of new supertalls. Not only is it hard to keep an average building watertight—it's extremely hard at 1,500 feet. And leaked water on a sleek, glass facade, which has no louvres or window panes to stop the crust, creates ice.
Even if a building doesn't leak, the sheer altitude contributes to the formation of a dangerous type of high-elevation ice often found on aircraft wings called "ice rime."According to a report from the Council for Tall Buildings (PDF), rime can be extremely dangerous:
[It] can range from thin dense sheets of hard ice that flutter to ther ground to bowling ball-sized chunks of white rigid ice that are less dense but make significantly larger projectiles. These ice formations are largely a result of wind-driven super cooled water droplets from visible cloud formations, fog, or mist coming in contact with cold building materials
The council concludes by warning architects to look more closely at meteorological predictions when designing—for us, keeping an open eye skyward should be enough. [Council for Tall Buildings; New York Times]
Lead image: Why yes, that is a Harlem Globetrotter on the 100th floor of One World Trade Center. Andrew Burton/Getty Images News.