Four people were taken to the hospital and about 200 more were evacuated from a residence hall and art building on the Gorham campus of the University of Southern Maine after a chemical spill was reported late Tuesday night.

Students working in the art department of Robie-Andrews Hall reported to USM police around 9:30 p.m. that about 20 gallons of silver nitrate spilled in the color processing lab on the first floor. The building also serves as a residence hall. Every person was evacuated within minutes of the report, said Bob Caswell, USM spokesman.

Silver nitrate is a poisonous chemical used to process photos.

Three students and a USM police officer were taken by ambulance to Maine Medical Center, where they were treated and released by 12:15 a.m., without any medical issues, Caswell said.

Students returned to the dorm around 12:15 a.m., and were re-evacuated around 1:20 after a false alarm was triggered. They were allowed back in at 1:50 a.m. The false alarm was not related to the chemical spill, Caswell said.

Crews from Clean Harbors Environment Services finished cleaning the spill around 2:21 a.m. The art department didn’t reopen until around 8 a.m. Wednesday.