School is back in session at a Bronx educational complex after mace was released in the lobby Tuesday, leaving several people gasping for breath.

The facility at 965 Longwood Ave. houses the Banana Kelly High School, Holcombe L. Rucker School of Community Research and New School for Arts and Sciences.

A fire chief said the substance was released into the lobby when students returned from a fire drill around 10:30 a.m. Investigators said they are unsure whether it was mace or a problem with the more than 100-year-old building, which school officials admit has a history of health hazards.

Hundreds of students were evacuated during the incident. EMS treated several people at the scene, including a security officer who officials say was sprayed.A teacher said she realized something was wrong when she saw a librarian gagging.

Classes resumed after the building was inspected. According to the Department of Education and EMS, the substance was mace.