Part of the adjacent pedestrian path was also cordoned off, and the 115th Street campus gates were closed.
A mechanic reported the shattered panel on Sunday, according to Marco Valera, assistant vice president for Facilities Operations.
Although the shattered glass remains in place on the north face of the building, near the fifth-floor ramp, administrators say there is no safety risk, and that the closures are only precautionary.
"We're fairly confident that there's no imminent danger [of] it falling out of place," said Marcelo Velez, assistant vice president for design and construction.
The glass is manufactured in layers, Valera explained, "like a pancake." Velez called it a "double pane" with layers of glass sandwiched around a plastic substance in the middle. Both confirmed that it was the glass layer inside Lerner that shattered, noting that the rest of the panel is intact and is holding the shattered layer in place.
Velez also explained that the safety hazard is minimized by the type of glass used in the construction of the panels. It shatters into pebble-sized pieces, like a car window, instead of shards that are large and sharp, like a broken bottle.
"It's tempered glass, so it's especially known for its safety characteristics," he said. "It fractures into small, relatively harmless fragments."
The ramps and other closed areas may be reopened as early as today, when a specialist is scheduled to arrive to inspect the glass, Valera said. However, Velez indicated that the glass might not actually be replaced for "several months."
"There are some stored pieces [of glass] in the basement of Lerner, but it's not likely that those pieces will be exact matches," Velez said. He added that replacement glass will probably have to be custom manufactured.
Valera indicated that the most likely cause of the breakage is a manufacturing defect rather than impact damage. He said that "it doesn't appear that it was hit by anything," suggesting instead that the cause might be "a defect in its construction that came out now after many years of being in place."
Velez elaborated. "We have two theories about the potential cause of the breakage," he said.
One theory holds that the breakage was caused by the inclusion of an impurity in the glass mixture.
Another theory holds that the breakage was caused by "edge damage," possibly resulting from improper handling.
Velez noted that a similar problem arose about two years ago, when another pane of glass spontaneously shattered in an apparently similar fashion. At that time, the breakage was attributed to the inclusion of an impurity--nickel sulfide--in the glass itself.
"The prevailing theory, at least in this office, is that it's going to turn out to be an inclusion again," Velez said.
"It's one of the reasons why this type of glass has instantaneous cracking," he continued. "It's rare but it's not uncommon."
His suspicion could be confirmed by the specialist scheduled to examine the glass today, but Velez said that "it may not be possible [to draw conclusions] until after the damaged glass is removed," noting that the defects in question would be "microscopic."
"We may never be able to actually determine the cause specifically between those two theories," he said. "It's probably unlikely that we're going to be able to know precisely."
However, if the specialist confirms that one of Lerner's panels has shattered due to "an inclusion" for the second time in the building's short life, administrators may have to face the possibility that it could happen again.