NEW YORK - Alongside the year-round fears of pedestrians in New York City - plummeting into a sidewalk cellar or being hit by a car - the winter season ushers in another potentially deadly menace: falling ice.

Ice can form on pretty much any New York City building, from low-rise tenements to luxury high-rises. Railings, rooftops, ledges and even windows provide surface area for drops of cold water to transform into ice.

The danger of whizzing icicles is not new: Police warned of “falling ice slabs” from Manhattan towers in 1939. But the threat is greater today because of a surge in new, angular towers that reach soaring heights and are built from materials like glass and steel that actually promote more ice growth. The acceleration of climate change may also contribute to icing issues.

One recent morning, police closed three blocks of Central Park South to both cars and pedestrians as ice fell from towers and crashed to the ground and into the park.

A piece of ice dislodged from a tower under construction in Midtown and struck a 55-year-old man in the face, cutting his mouth and lips.

While ice and snow may melt upon contact with a warm sidewalk or street, they adhere to the cold nooks and crannies of a building. It is also easier to form on energy efficient buildings because they retain heat that otherwise could melt ice.

Then, when the sun appears, the surface below the ice heats up, allowing the ice to release. Now the ice is plummeting down, into something, or someone, below.

Over the past decade, 10 so-called supertalls - towers at least 300 meters (984 feet) high have been built in New York City. Another six are under construction. And all are energy efficient and built with glass and steel.

On a bitterly cold day in January 2018, Coltrane Nadler was turning a corner in lower Manhattan when he spotted a brown chunk of ice fall from the sky and slam into his parked Chevy Equinox. Windows exploded and the back of the roof crumbled. The ice chunk shattered.

His car was totalled, but Nadler, fortunately, was not inside. “I would have been traumatised for life,” Nadler, 20, said. “It would have totally killed some people.”

The descent of icy weapons

An object that falls from a building, such as a piece of ice, does not have to drop from tremendous heights to accelerate to dangerous speeds. Frank Moscatelli, a clinical professor of physics at New York University, said that ice could reach its maximum speed, between 60 and 70 mph, from the top of a 15-floor building.

It would travel the same speed at that height as it would if it fell from the tip of the city’s tallest building, One World Trade Center, whose spire climbs to 1,776 feet, Moscatelli said. That’s because of terminal velocity, the maximum speed of a freely falling object.

But whether that ice bounces off a pedestrian below or crushes him depends on the size of the ice. “When the object hits you at, say, 64 mph, it matter if it’s a penny or a brick,” Moscatelli said.

On February 4, 1994, Jill Gardenfeld, then a 24-year-old advertising analyst at Macy’s in Herald Square, was knocked unconscious by a 2-foot-wide ice slab. The jagged piece fell 21 stories, or roughly 300 feet, and struck her in the chest and shoulder, nearly killing her.

Gardenfeld survived, but spent two months in the hospital, underwent 14 operations and received 114 units of blood, her family told Newsday. She never regained the use of her left arm.

This month, pedestrians walking outside several Manhattan towers have encountered signs and tape advising them to take alternative paths to avoid falling ice.

Public is alerted

The city’s Department of Buildings alerts building owners, construction companies and landlords when the weather is ripe for snow or ice to melt and fall. In fact, city law requires property owners to clear snow and ice to prevent accidents.

They must clear roofs and overhangs, as well as remove ice and snow from trees and gutters.

“Building owners have a legal responsibility to keep their properties safe for the public, which includes taking steps to prevent ice and snow on their properties from posing a falling hazard,” the department said in a statement.

A building’s owner can be held liable for damage and injuries caused by falling ice. Nadler said that the ice that struck his car had fallen from a tall residential building, whose owners assured him that they would buy him a new car. But Nadler said that working with the building’s insurance became a hassle, so he bought a newer Equinox on his own.

In 2014, a man hit by falling ice from a building on West 48th Street in Midtown later sued the building’s owner and settled the case out of court. (The family of a man killed in 1994 by falling ice from a Chicago tower received $4.5 million in a settlement.)

Older structures can also pose a hazard. Last week, a piece of debris fell from a 17-story building built in 1915 that, officials said, had recently been fined by the city for its unsafe facade. The debris broke off and tumbled to the ground, killing a 60-year-old woman.

Recent studies have warned that new design features on supertall towers, such as smooth exteriors and sloped surfaces, increase the amount of cold surface area for ice to form and snow to collect. Older buildings have fewer angles and were made with stone and concrete that absorb heat, keeping the surface warmer.

The architecture of safety

Mike Carter, founder and director of Microclimate Ice and Snow, an architectural consulting company based in Canada, said that every building behaves differently in winter storms, depending on its materials, its height and location.

In New York City, he said, freezing mist and wet snow cling to buildings, latching on to the cold exterior, even smooth windows, and attaching to ledges and parapets. Snow will also melt on a warm surface on the building and then slip down to a colder area and freeze again, he said.

Carter, who said he had worked on numerous buildings in Manhattan but declined to identify them, said that building managers must understand how their building functions in the cold so they will know when and where ice and snow could collect.

“You can’t prevent ice and snow from falling,” Carter said. “There is no magic bullet.”

The New York Times News Service