Why does the broken glass fall from the Bethesda Building?

Montgomery County officials are trying to figure out why glass panel railing on relatively new mid-to-high-rise buildings in downtown Bethesda shatter spontaneously, and glass raindrops fall on the sidewalk below.
County construction officials said they are investigating whether there is any connection between the windows and large glass panels of three buildings built within a half-mile radius of the Bethesda subway station in the past two years, all of which were built in 2014. The two owners stated that their engineering consultants found that the failed glass had manufacturing defects.
In an incident on August 22, a 12-year-old girl standing outside the entrance to the Harris Teeter grocery store was slightly injured when a pebble-sized glass was dropped from the balcony railing of the 9th floor apartment. Recently, the glass canopy of the same building as the Flats 8300 apartment at 8300 Wisconsin Avenue was found broken above the main entrance on Tuesday, on the same sidewalk as the school station. Although the glass shattered, it did not fall.
On July 7, on the eighth-floor balcony of the Cheval Bethesda luxury apartment on the 17th floor at 4960 Fairmont Avenue at the corner of Old Georgetown Road, part of the glass railing fell.
In the spring of 2017, there was the first report of glass falling in an office building at 4500 East-West Hwy. Three panels of the glass curtain wall then shattered and fell on the sidewalk, while the other eight panels were broken but did not fall. In May, the owner of the DC-based Carr Properties building agreed to replace the types of glass panels found to have manufacturing defects as part of the county investigation.
It is not clear whether the glass is all manufactured by the same company, as the owners of all three buildings have refused to provide the Washington Post with the name of their glass manufacturer.
"We need more answers," said Hardi Mansouri, acting director of Montgomery's licensing services. "Why it happened suddenly is something we are trying to figure out... This is a life and safety issue."
Officials in Washington, Prince George County, and Northern Virginia state that they do not remember any similar glass failures in recent years, and searches for international news reports have found relatively few such cases. However, the Bethesda incident is similar to the Baltimore case. According to news media reports, in October last year, glass fell from a broken window on the eighth-floor window of the 20-story Exelon building in the downtown area, injuring two people.
The Bethesda case shocked residents of the inner city, the area is experiencing a boom in high-rise buildings, including several buildings with glass curtain walls.
"How likely is it that you have problems with all three buildings in a downtown area?" said Amanda Farber, a Bethesda resident who has been tracking the problem. "I want to know what is in common. They all happen in different weather conditions and at different times of the year. Is it a defect in the glass itself?"
Another Bethesda resident, Paige Coulman, said she saw glass particles fall on August 22, falling on about four adults and four children outside the Flats 8300 apartment building. .
Cullman, who was driving by, said that she saw the group of people running across the road with their heads in their hands. Cullman said that on Tuesday morning, she was surprised to see a broken glass canopy at another entrance to the same building.
Mansouri said that in all incidents, the glass fell into small particles, rather than larger and more dangerous fragments, because the glass was tempered in accordance with the requirements of international building codes.
These three buildings now have scaffolding and canopies to protect the sidewalks underneath. Some are ordered by the county government, and some are installed voluntarily by the owners.
According to media reports, in the Baltimore case, the owner of the Beatty Development Group in Baltimore found possible manufacturing impurities in multiple glass panels. A spokesperson for the company could not be reached this week.
One of Carr's consultants found the same defect-the presence of nickel sulfide-in the falling glass on the 4500 East-West Hwy facade. According to experts, when the glass production process is contaminated, tiny nickel sulfide balls will form in the glass. Over time, the glass will crack or break without warning.
According to a memo sent by the developer to the residents of the building, a consultant for Duball Fairmont, the developer of the Cheval apartment complex in Reston, also discovered that nickel sulfide may be the cause of the broken balcony railing on July 7.
A glass expert said that finding out which company or companies made the problematic glass will be the key, especially if nickel sulfide is found to be the root cause of all three buildings.
George Dotzler's Construction Research Laboratory in Miami, which is responsible for testing products used in building facades, said that problems caused by nickel sulfide were more common in the 1960s. However, he said that he has found them "very rare" since the 1970s, when American glass manufacturers found a way to ensure that nickel sulfide was not left behind.
But Dotzler said that in the past five to six years, he has seen more cases of glass produced by Chinese companies, and the price is usually lower.
"This really won't happen to European or North American or even South American [glass] manufacturers," Dotzler said.
Dotzler emphasized that he knew nothing about the Bethesda case, and he said he also wanted to know why the balcony glass would fall when it shattered.
Carr, the owner of the 4500 East-West Hwy. office building, said he expects to replace the defective glass next year.
Duball President Marc Dubick provided Cheval residents with a detailed memo about broken balcony railings. The memo stated that the developer was replacing all glass railings in the building "out of prudence."
Milton Schwarz, chairman of Cheval Apartments' board of directors, said he was satisfied with the company's response.
Greenbelt-based Bozzuto, who manages the Flats 8300 apartment, said it was expanding the building’s protective scaffolding “as an additional precaution” in light of the broken glass canopy found on Tuesday. Mansouri said the county is also considering it as a Item command.
"We have been working closely with construction engineers and materials scientists to diagnose problems and investigate further," Bozzuto said in a statement.
The statement stated that the company also kept in touch with the family of the injured 12-year-old girl.
"Our company is built on the values of care and care," Bozzuto said. "As a property manager, the safety of our residents and everyone who visits the community is our top priority."