A three alarm fire tore through a St. Louis university research building Thursday evening.

The fire was on the third floor of Macelwane Hall, a building on the St. Louis University campus. In a Periscope video, Captain Garon Mosby said they were told chemicals were on the second floor of the building.

It's still unclear how the fire started, but school officials confirm the third floor was under construction. No one was in the building when crews arrived on the scene.

The fire started in the Neuroscience lab and damaged faculty offices.

There was concern about the presence of chemical's in this science building. As a result, several fire fighters were decontaminated as they left the building, as a precaution. An investigation now begins into the cause of the blaze.

It took about 75 firefighters to contain the fire.