The developer of The Bravern complex in Bellevue said the cause of a glass panel shattering and falling from a seventh-story apartment balcony Tuesday was unrelated to the crash of a 30th-story glass panel last December.

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For the second time in eight months, a glass panel has fallen from a balcony railing on a residential tower at Bellevue’s upscale mixed-use project, The Bravern.

Once again, no one was hurt.

In the latest incident, pieces of tempered glass fell from a seventh-floor balcony and landed on a residential roof about 6:15 p.m. Tuesday.

The glass broke into small pieces “as it is designed to do when broken,” Greg Kletzly, senior investment manager for developer Schnitzer West, said in a statement.

But unlike the December incident, attributed to faulty fasteners, the glass panel that broke Tuesday was apparently shattered by an unknown object hitting the glass from above, Kletzly said.

“These appear to be unrelated incidents,” he said. Both accidents occurred at the residential North Tower.

Two apartment towers, originally intended as condos, opened at The Bravern in 2010. The development also includes The Shops at Bravern and two office towers leased by Microsoft.

Kletzly’s statement said the company concluded an object broke a seventh-floor balcony panel Tuesday based on the testimony of two eyewitnesses.

Kletzly said later the witnesses didn’t actually see a falling object but it was their “supposition” that an object caused the fracture. He said the object hasn’t been found but the company is continuing to investigate.

Based on briefings from Schnitzer, Bellevue Inspection Services Manager Doug Fox said this week’s incident appeared to be the result of an outside impact because most of the broken glass landed on the balcony deck.

In the earlier incident, a glass panel fell from the 30th floor, crashing into a 23rd-floor railing and dropping small pieces onto a pet area and the roof of the adjacent Meydenbauer Center.

As a safety precaution, glass panels of up to 3 feet by 4 feet in size have been strapped to their metal frames on the two residential towers as the developer prepares to strengthen balconies with a different kind of fastener.

“We had a failure of one balcony. We think it’s prudent to shore up all the balconies to assure safety. That repair will be ongoing through the fall,” Kletzly said.

IBA Consultants West, hired by Schnitzer to determine the cause of the December accident, reported in February that the wrong kind of screwlike fastener was used to attach the railing post to the bottom rail.

Four fasteners sheared off, allowing the glass panel to loosen. The fasteners were corroded, and laboratory tests showed they contained excessive amounts of hydrogen, which made them brittle, according to the IBA report provided by the Bellevue Department of Development Services.

IBA and third-party reviewer DCI Engineers recommended that railing manufacturer Sapa design a repair plan that would include attaching posts to rails with the noncorrosive stainless-steel screws originally specified by Sapa.

The reports from IBA and DCI did not suggest that the use of tempered glass contributed to the December mishap.

In Toronto, where 30 tempered-glass balcony panels have shattered on 11 buildings since last summer, The Toronto Star reported in June that Ontario has tightened the building code to require heat-strengthened laminated glass for railings that project beyond a concrete balcony slab and require heat soaking of tempered glass used near a slab edge to reduce the likelihood of spontaneous breakage.

Tempered-glass balcony panels shattered in July and September of last year at Seattle’s Four Seasons Hotel and Private Residences, which closed off balconies until fixes were made.

Until repairs are completed at The Bravern, North Tower resident Nate Webb said he is concerned about the safety of his family’s seventh-floor patio and the safety of shoppers below the building.

“If my balcony glass fell, it would fall directly into the walking areas of their retail space,” Webb said.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com