A day after 11 students and a teacher were taken to the hospital after a light fixture containing toxic PCBs began emitting smoke at a Harlem school, the city announced that it would speed its timeline for replacing the fixtures in school buildings.

The city did not draw a connection between the incident at P.S. 123 in Harlem and the announcement, nor did it specify how quickly schools would be cleared of the toxic chemicals, which have been the subject of sustained protest, disputes between schools, and at least one lawsuit in recent years.

“The city has determined it can complete light fixture replacement projects in the remaining 645 buildings well before the previously announced timetable of 2021,” said Elizabeth Thomas, a spokeswoman for the city’s law department, in a statement announcing the change. “Due to ongoing mediation, we cannot provide more information at this time.”

The announcement also comes as City Councilman Robert Jackson, who chairs the council’s education committee, prepares to ask the State Education Department to investigate the city’s handling of the PCB lights. Jackson plans to hold a press conference announcing the petition outside P.S. 123 on Thursday.

The incident at P.S. 123 was only the latest to raise fears that the aging light fixtures are exposing students to toxins. Last week, a light fixture at a Cobble Hill school emitted smoke. Last month, a PCB-ridden light fixture was replaced on an emergency basis at P.S. 32 on Staten Island after school officials reported that it smelled bad.

The city has cleared about 110 school buildings of the chemicals, which can cause cancer, in the last year and a half. Officials have said their capacity to clear schools of PCB lights has been constrained both by money and by the fact that PCB abatement can happen only when schools are not occupied by students.

About the pace of PCB removal, Department of Education Deputy Chancellor Kathleen Grimm said at a recent City Council hearing, “Can we see if that could be increased somewhat if there were more resources? Yes. Can we do everything in the summer of ’14? No.”