Another Philadelphia public school building has been closed after damaged asbestos was discovered inside.

Franklin Learning Center on North 15th Street will shut to students and staff through Jan. 2.

Environmental staff from the Philadelphia School District on Tuesday “identified an imminent hazard involving damage to asbestos-containing pipe insulation” at FLC. The damage was found inside an air shaft connecting the school’s attic to its fan room.

FLC is the fourth school this year to have its building shut down because of asbestos. Benjamin Franklin High — a separate school down the street from FLC — and Science Leadership Academy, the magnet school that was to share Franklin High’s North Broad Street building, were shut for weeks. Students at both schools have returned to classes but in temporary locations. Their building is expected to reopen next year.

The closure comes as more than 200 Philadelphia high school students plan to head to Harrisburg on Wednesday to lobby lawmakers over asbestos and lead in their schools.

“Upon discovery, the fans were immediately shut off and taken out of service,” district officials wrote in a letter to parents and staff.

Because shutting down the fans affects the district’s ability to heat the building, “and in an abundance of caution,” the call was made to close the school immediately. Students had been scheduled to have classes through Friday and staff were also scheduled to be in the building next Monday for a teacher in-service day.

“We understand this process may be challenging for the school community,” the district letter said. “However, we are taking all the steps necessary to ensure that the school is safe, and the health of our students and staff remains a top priority.”

T.M. Peirce Elementary, in North Philadelphia, also closed this fall after asbestos was found at the school. School officials took heat over how the Peirce situation was handled — many parents learned about the environmental hazard in their midst from an Inquirer story, not from the district, whose officials acknowledged they had been alerted to the problems but said they lacked the resources to respond immediately.

Since then, Superintendent William R. Hite Jr. has come up with an environmental action plan that requires, among other things, that all reports of damaged asbestos be handled within 24 hours. Asbestos is not considered a health risk when kept in good condition, but when damaged, the material can release microscopic fibers that can cause cancer when inhaled.

Jerry Jordan, president of the city teachers union, said in a statement that the FLC situation “is emblematic of the emergency conditions in far too many of our school buildings.”

“Today’s discovery reflects both the progress we have made and the deeply flawed system in which we are operating,” Jordan said. “For the first time in recent memory, the district quickly reported to us the discovery of an immediate environmental hazard and committed to collaborate with us on a plan for swift remediation. However, it is problematic that our recommendation to conduct this assessment was made months ago, and only just took place.”

Over the last seven months, more than 50 complaints of environmental problems at FLC have been reported to the Philadelphia Federation of Teachers — not just asbestos, but also mold, mildew, crumbling walls, damaged lead paint, and thermal control deficiencies. FLC staff also complained of a white powdery substance coming out of the heating vents in classrooms and other student-occupied parts of the school, according to Jerry Roseman, director of environmental science for the PFT’s Health and Welfare Fund, which monitors building conditions.

When FLC teachers returned to school this year — amid news that a longtime teacher from Meredith Elementary in South Philadelphia had been diagnosed with a rare asbestos-linked cancer — they grew increasingly concerned about asbestos and the white dust coming from the vents. In response, Roseman said, he recommended that district officials conduct a top-to-bottom environmental inspection of the building, with a focus on the heating and ventilation system.

On Tuesday morning, an environmental inspector from a firm hired by the district discovered what appeared to be asbestos debris at the bottom of an air shaft. Later that day, district officials asked Roseman to take a look. They used binoculars and flashlights to peer about 60 feet down the shaft. They noted heating pipes with asbestos insulation and determined that the debris was likely asbestos. It is unclear how long it had been there and whether any fibers had moved to other parts of the building via the heating system, Roseman said.

Roseman said he was working with district officials to develop a plan for cleaning up the debris and conducting air tests. They plan to take air samples in the school’s fan room and the auditorium, which is the space closest to and potentially most impacted by the debris in the shaft.

“If those two areas do not have asbestos fibers floating in the air, then we can probably say that there is no concern with other parts of the building,” Roseman said.

FLC, built in 1908, is filled with asbestos material. Under federal law, the district is required to thoroughly inspect schools for asbestos every three years, noting its location and condition, and then conduct visual walk-throughs to make sure nothing has changed every six months. District reports show that inspectors repeatedly noted damaged asbestos in various locations inside FLC in recent years. The district removed some of the damage, records show.

Staff writer Dylan Purcell contributed to this article.