The Engineering Center at the University of Colorado was closed for several hours Tuesday after a chemical spill prompted an evacuation.

The chemical spill was reported a little after 11 a.m.

One of four students in a lab in the center’s chemical wing accidentally dropped a 100-milliliter glass bottle of acryloyl chloride, which turns into hydrochloric acid when it interacts with the air, said CU police spokesman Ryan Huff. The students suffered some eye irritation and pulled the fire alarm.

As a precaution, CU officials decided to evacuate the building at 11:34 a.m., Huff said.

Officials initially thought nobody was injured, but Huff said a female student was in the basement and was not aware the building was being evacuated. She later reported a headache and was taken to Boulder Community Hospital.

Huff said the four students in the lab were evaluated and did not need medical attention.

The Boulder County Hazardous Materials Team entered the building around 2:30 p.m. and determined that only the chemical wing constituted a health threat. The building was reopened around 3 p.m., the spill was cleaned and the chemical wing was reopened around 3:45 p.m.