CHICAGO (CBS) — The Chicago Fire Department initiated a hazardous materials response at Morgan Park High School on the South Side after several students were sprayed with an aerosol irritant, possibly pepper spray or mace. It’s the second day in a row students at Morgan Park were sprayed with an irritant.

The Fire Department said today’s incident happened around 11:45 a.m. Nine students were taken to the hospital as a precaution.

Yesterday, two Morgan Park students were taken to the hospital after firefighters responded to another incident involving an aerosol irritant around 1:15 p.m.

In a letter to parents, the school said police and fire officials were investigating yesterday’s incident.