At least a dozen students were medically evaluated Tuesday after pepper spray was released inside Jamaica High School in Queens, said fire officials.
It is not clear if anyone was sickened by the chemical irritant or who was responsible for spraying it.
Police and EMS officials were called to the school on Gothic Drive a few hours into the school day.
Pepper spray can cause asthma attacks, difficulty breathing and temporary blindness.
On March 1, an eighth-grade student pepper sprayed classmates inside a classroom at P.S./I.S. 218 in the Concourse section of the Bronx Friday.
Some of those sprayed with the chemical irritant suffered asthma attacks, the FDNY said.
Medics took 10 students, including the suspect, to Lincoln Hospital where they were treated and released, according to the Department of Education.