Five students and three adults at Burnet Middle School in Austin were taken to the hospital for burning eyes and nausea after a chemical substance was found in a student restroom.

KXAN-TV reports that the school was briefly evacuated after what police called an “acid bomb” was discovered. Fire officials were called in to investigate and remove the chemical, and students resumed classes shortly after 10:45 a.m. The restroom has been cordoned off.

Officials found a plastic container filled with acid, but have not identified what the substance was.