A toxic chemical spill and small fire forced students, professors and staff to evacuate the Mallinckrodt lab building on Friday afternoon.

No injuries were reported, but the Cambridge Fire Department (CFD) kept people out of the building for several hours until the chemical had been cleaned up and smoke had cleared.

The chemical spilled was tetrahydrofurane (THF), a highly flammable liquid often used as a solvent. On the zero-to-four scale used by the National Fire Protection Association, the substance is rated a three (severe) for flammability and a two (moderate) for health risks.

The spill occurred in the lab of Assistant Professor of Chemistry and Chemical Biology Matthew D. Shair, located on the third floor of the building.

A student accidentally knocked over a container of the chemical, spilling it on the floor, according to John J. O'Donoghue, a deputy fire chief with the CFD. Other students in the lab attempted to clean it up, but the THF was spilled near a stove and started a small fire, O'Donoghue said.

Students used a fire extinguisher to put out the flame and then pulled the fire alarm, O'Donoghue said.

The fire department arrived at the scene at 2:30 p.m. with four fire engines, two rescue trucks and a Hazardous Materials unit.

The fire had already been extinguished when firefighters arrived. However, because of the toxicity level of THF, the Hazardous Materials unit felt it was necessary to do a special clean-up procedure.

O'Donoghue said the students acted quickly in extinguishing the fire and exiting the area. "They did a good job", he said.

The student who caused the spill declined to comment.

It is unclear how many people were in the building when the accident occurred. There were approximately 10 people in the immediate area, according to Henry S. Littleboy, the safety officer for the chemistry department.

The incident comes only five months after an accident in Converse Hall, a lab building adjacent to Mallinckrodt. An explosion occurred there in early May while students were taking an annual inventory of chemicals. Three students were treated at Massachusetts General Hospital following that blast.

Most people were unaware that a spilled chemical caused Friday's fire until they saw the Hazardous Materials unit arrive. Firefighters double-checked the scene when they arrived to be sure no one had ignored the alarm and stayed in the building.

THF is a mild irritant to the nose and throat. However, O'Donoghue said the chemicalitself posed little harm to the students.

"It was more of a fire hazard than a healthhazard," he said.

--Marc J. Ambinder contributed to thereporting of this story.