After a large window shattered and fell from a new, high-profile Inner Harbor tower last week and injured two people, the developer launched an investigation to determine why.
Experience in this building and several others around the country in recent years suggest flaws in the glass might be responsible.
The Beatty Development Group, which built and owns the 20-story Exelon building at Harbor Point, said that was the problem before. A total of six windows in the building have failed, and imperfections have been found on dozens more.
The developer said “nickel sulfide inclusion” was responsible for breaks in two interior windows in the building. That happens when trace elements form tiny balls during the glass manufacturing process and cause what seems like a spontaneous break over time.
A cause has not been determined for two other exterior windows that also broke in the same building before last week’s failure, according to Beatty Development.
After the earlier breaks, the developer hired an investigator to inspect all of the building’s 7,500 panels of tempered glass for chips, cracks and other imperfections, and after eight months found 66 problem panels that were replaced.
Chris Seiler, a company spokesman, said in a statement that the inspection process has begun anew.
No information has been provided about the two injured building workers.
Beatty “is working with the glass contractor, installer and experts to re-evaluate the situation and recommend possible corrective action,” Seiler said. “In the interim, we have placed extensive scaffolding around all affected areas of the building to insure public safety.”
The scaffolding around the building is designed to protect those living and working in the building. The regional headquarters of power giant Exelon anchors the building with 1,500 employees, but it’s also home to 103 apartments and several ground-level retail shops.
It’s not clear how often windows fail across the country, though there have been media reports in recent years in several cities. Local governments don’t typically inspect the windows as part of code enforcement or permitting or even respond when one falls. And testing is not generally required, though many developers hire firms anyway.
Tammy Hawley, a spokeswoman for the city’s Department of Housing and Community Development, said the agency inspects commercial buildings for footings and foundations, electrical, plumbing, heating infrastructure, fire-blocking and other things. It doesn’t test windows.
There are model codes and industry standards that govern windows, however. Commercial building generally calls for hardened glass that is stronger than regular glass and glass that is tempered to shatter into tiny pieces rather than fall as shards that can be far more dangerous.
Most developers try to exceed whatever local codes exist and adhere to the standards, said George Dotzler, director of operations for the Construction Research Lab in Miami, who has been testing windows for 30 years, including some in Baltimore. That means far stronger glass for buildings in hurricane-prone areas of Florida, for example.
He was not familiar with the Exelon building, but said he’s heard of an increasing number of window failures around the country. For failures generally, he said he suspects an increase in foreign-made glass by companies without requisite experience. Sometimes there are outright counterfeit products on the market, he said.
Imperfections were more common among windows made by North American manufacturers decades ago, Dotzler said. Now he rarely finds such flaws when he tests domestically made windows.
The tiny imperfections, usually around the edges, can’t be seen readily. They will develop into larger cracks with installation or over time from weather or other conditions, he said.
“We had a spate of failures in the ’50s and ’60s, and the construction industry learned to avoid them and it’s not been a problem again until recently,” Dotzler said. “Overseas manufacturers, some in developing countries, have to go through a learning curve.”
He said developers might not realize the source for their windows, but might start paying closer attention and instruct contractors to go to known manufacturers to ensure safety, even if it’s a higher cost.
Daniel J. Lemieux, a principal at Wiss, Janney, Elstner Associates Inc., an Illinois-based construction services firm, said the developer’s design team determines the technical specifications for a project, which includes the performance requirements for materials, and then the contractor is responsible for ensuring the plans are followed.
He said there are many reasons windows could fail, even if everything was done according to those specifications.
The presence of nickel-sulfide inclusions in tempered glass “is one source of thermally-induced, spontaneous glass breakage that is relatively well understood in the industry yet still difficult to identify or predict until breakage occurs,” he said. He said a kind of testing can be done by manufacturers before glass panes are fabricated that can minimize the risk.
For its part, Beatty Development will continue to investigate specific potential problems and evaluate its next steps for the windows but has not committed to replacing all 7,500 window panes, which came from a U.S. manufacturer, Seiler said.
“The curtain wall glass system utilized on the building is a complicated structure,” he said. “Replacing the glass post-installation carries a certain amount of risk. We are evaluating all possible solutions.”