CHICAGO (CBS)– Three people were hospitalized and a level one hazmat was called at Morgan Park High School after a substance was sprayed or released into the air, according to a Chicago Fire Department spokesperson.

The fire department said the three people taken to the hospital, all female, were listed in good condition.

One student described the incident as chaotic and said students were choking. He said the school was on lockdown, so students could not leave their classrooms.

This is the fourth incident in seven days. Two students were taken to the hospital Tuesday afternoon, after someone sprayed an unknown substance at Morgan Park High School.

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.”