People in U.S. cities facing one of the most brutal winters on record have been dealing with something far more dangerous than snow: ice falling from skyscrapers.
Several streets around New York's new 1 World Trade Center, the nation's tallest building, were closed Wednesday morning when wind-blown sheets of dagger-shaped ice hit the pavement near the 1,776-foot (541-meter) structure.
Frightened pedestrians ran for cover. The streets reopened by midafternoon.
Around the country, sidewalks around high-rises in cities have been cordoned off with yellow caution tape because of falling icicles and rock-hard chunks of frozen snow. Experts warn it could get worse over the next few days as a thaw sets in over much of the country.
"The snow starts to melt and the liquid drips off and makes bigger and bigger icicles, or chunks of ice that break off skyscrapers," said Joey Picca, a meteorologist at the National Weather Service in New York, which has had 48.5 inches (1,230 millimeters) of snow since the start of the year.
Some architects say newer, energy-efficient high-rises may actually be making the problem worse.
"They keep more heat inside, which means the outside is getting colder and that allows more snow and ice to form," said engineer Roman Stangl, founder of the consulting firm Northern Microclimate in Cambridge, Ontario.
Stangl helps developers choose shapes, slope angles and even colors - darker colors absorb more melting sunrays - to diminish ice formation. High-tech materials can be also be used, such as at Tokyo's Skytree observation tower, where heaters were embedded in the glass to melt the ice.
Such options are not always possible in older cities with balconies, awnings and stone details.
Barry Negron said he saw ice hanging perilously off a four-story building near Rockefeller Center last month and was trying to warn other pedestrians when he was hit in the face with a sharp, football-size chunk. Cuts across his nose and cheek required 80 stitches.
"I panicked because I saw blood on my hands, and more coming down," said the 27-year-old. As he lay on the pavement, "I heard two young ladies yelling, 'Oh, my God, oh my God, help! There's a lot of blood!'"
Exactly how many pedestrians are hit by falling ice is not clear, but dozens of serious injuries are reported annually. It's a perennial problem in St. Petersburg, Russia, where dozens reportedly are injured or killed every year.
Seven people were injured in 2011 near Dallas when huge sheets of ice slid off the roof of Cowboys Stadium. Fifteen people were injured in 2010 by a shower of ice from the 37-story Sony Building on New York's Madison Avenue.
Outside Chicago's 100-story John Hancock Center last month, people scrambled with backpacks and purses over their heads to avoid falling ice. On Tuesday, signs warning pedestrians of falling ice stood outside nearly every skyscraper and other tall building downtown as temperatures pushed above freezing for the first time in weeks.
"This happens all over the country, all over the world, in cold climates," said architect Chris Benedict, who accounts for ice buildup in designing new structures.
In other news: Ice sheets fall in Texas as the polar vortex attacks US