At 4:45 Monday afternoon, Anastasia Ulanowicz's children's literature class was discussing "Little House on the Prairie" in Turlington Hall Room 2350.
At 4:46 p.m., a loud alarm made Ulanowicz jump.
A chemical spill in the basement of Turlington caused the entire building and the adjoining restaurants to be evacuated.
The building was closed for about an hour while UF Environmental Health and Safety employees cleaned up the spill.
Nader Abo Dya, 35, and Suvendu Biswas, 27, were combining chemical compounds in Room B115 when one of them dropped five grams of 2-Chloroethyl Isocyanate, a liquid compound that is combustible and moisture-sensitive.
The compound's uses range from chemotherapy treatment to the manufacturing of foams, paints and insulation materials, according to the Centers for Disease Control and Prevention.
It can be harmful if swallowed, inhaled or absorbed through the skin.
The two students handling the compound complained of burning eyes and irritated lungs.
University Police Officer Daymon Kizzar was notified of the incident at 4:41 p.m.
He arrived on the scene four minutes later and pulled the fire alarm to evacuate the building.
Turlington's old fire alarms, which sound more like the low-pitched buzz of a loud generator than the shrill alarms of newer buildings, confused some students and professors about whether to leave the building or stay put.
"Our professor initially thought we should just stay in class," said Erin Domaracki, an 18-year-old exploratory freshman who was in Geography of Africa when the alarm sounded.
Domaracki and her classmates eventually joined the other students slowly filing down hallways and stairwells to stand outside Turlington.
Some classes were immediately canceled as UPD officers announced the building's closure. Others, like Ulanowicz's class, picked up where they left off on the benches near the University Auditorium.
UPD blocked southbound traffic on Newell Drive for about an hour and a half, causing some bus routes to be diverted.