The Evanston Fire Department and the Northwestern University Police Department responded to the Nanofabrication center Tuesday afternoon after a chemistry lab reaction exploded and triggered fire alarms, said Chuck Loebbaka, director of NU media relations.

The explosion occurred in a laboratory on the third floor when a reaction between sulfuric acid and hydrogen peroxide caused flames and smoke, Loebbaka said. A fire alarm was pulled after the flames were seen.

No serious damage was caused by the reaction, Loebbaka said. Four EFD trucks, two UP cars and an ambulance were seen outside the building by 3:30 p.m.

The building was evacuated between 3:15 and 3:30 p.m., according to witnesses outside the building. Students and faculty were back inside by about 4:30 p.m., Loebbaka said.

Witnesses said they heard a loud noise just before the fire alarms went off. Flames were seen in the lab but were contained underneath the chemical hood above the experiment area.

There was no water damage, Loebbaka said. Firefighters used a dry chemical to put out the flames, he said. Witnesses said they did not see any sprinklers turn on.

Officials from the office of Northwestern Risk Management and Evanston emergency services also arrived on the scene.

Reach Laura olson at [email protected].