CENTER POINT, Ala. (AP) — Four students were taken to a hospital in Birmingham after mercury spilled from a broken thermometer at a school.

The principal of Center Point High School, Van Phillips, tells news outlets that someone broke a thermometer in a chemistry class on Thursday.

Four ninth-graders who may have touched the substance were taken to Children’s of Alabama as a precaution.

Students were moved to another part of the school so classes could resume, and a cleanup crew was brought in to clean-up the mercury.

Mercury is classified as a hazardous material. Inhaling vapors from the liquid metal can cause respiratory problems and nervous disorders in more serious, repeated cases.