CHICAGO (CBS) — For the fifth time in eight days someone released an aerosol substance inside Morgan Park High School.

This time 16 students reported injuries. Three were taken to the hospital.

After the incident student were told to stay in their classrooms while officials ventilated the building.

Police are questioning one of the two alleged offenders.

School officials say they are implementing additional safety screening measures.

Chicago Public Schools released the following statement regarding the incidents:

“CPS is committed to ensuring students have access to a safe learning environment, and district staff have been on-the-ground supporting the school community since last Thursday. The district is taking this situation very seriously and we will continue to engage the school community and implement additional security measures until the issue is rectified.”

Three people were hospitalized Wednesday when a substance was sprayed or released into the air. One student described the incident as chaotic and said students were choking.

Two students were taken to the hospital Tuesday afternoon, after someone sprayed an unknown substance.

Last week, police and fire crews were called to Morgan Park High School two days in a row — on Thursday and Friday — after students were sprayed with an aerosol irritant, possibly pepper spray or mace.

Morgan Park High School officials sent an email to parents, regarding Thursday and Friday’s incidents, stating “we are working with CPS Safety and Security to develop a plan of action to prevent similar incidents from occurring in the future.”