Two Simeon High School teachers suffered burns after an small explosion following a chemistry experiment.
Chicago firefighters say the two teachers were performing the experiment in a third floor lab or classroom Friday afternoon. No students were in the room at the time.
Students say they heard the fire alarm go off and thought it was just a drill. They left the school and word soon spread that two teachers had an experiment explode on them.
"I heard it a little...it was just like a boom," said Michael Flyling, a student who was in the classroom next door.
After two hours, students were let back inside the school.
Firefighters say there weren't any flames, but the teachers likely suffered chemical burns on their faces and arms.
The fire department says both teachers are expected to be O.K.
No comment from Simeon High School.