A small explosion shut down McLane Hall, located in the north end of the California State University, Fresno campus, just behind the Kennel Bookstore.

Classes and offices were evacuated for about 40 minutes around noon Thursday after a classroom experiment resulted in a small explosive chemical reaction. The explosion was contained within a venting hood.

No one was injured.

The reaction triggered fire alarms although there were no flames.

Students, faculty and staff responded to the alarms by following the building evacuation plan and waiting in designated areas away from the building while Fresno Fire Department personnel investigated.

The safety and alert systems worked as designed, one investigator said as evacuation was lifted and the classroom and office building were re-occupied.

Some students didn’t realize the possible severity of the situation.

“I think this is some sort of fire drill,” a nearby student remarked.

McLane Hall houses many of the labs used for Fresno State chemistry courses.

It is not known at this time in which course or in which classroom the experiment that initiated the small explosion took place.

Fresno State News contributed to this report.