A small flash fire occurred in the Paul G. Allen Center for Integrated Systems annex Thursday afternoon, setting off smoke detectors and forcing the evacuation of some 150 people from the annex and the main CIS building. There were no injuries.

Palo Alto Fire Department, the Stanford Department of Public Safety and University Environmental Health and Safety officials, concerned with potentially hazardous materials in the lab, responded, cordoning off Via Ortega and parts of Serra Mall from traffic for about two hours.

According to Larry Gibbs, the associate vice provost for environmental health and safety, and other CIS staffers, the fire broke out just after 1 p.m. when a group of lab researchers attempted to clean a thin metal liner that is part of the molecular beam epitaxy (MEB) equipment that the lab houses.

When scraping a small amount of residue off of the interior of the chamber, a fire ignited within the vessel, causing a large amount of smoke to exit.

The researchers, at least several of whom were doctoral students, pulled the fire alarm and left the building, said fire department spokeswoman Susan Minchall.

The researchers were wearing respirators and Tyvek suits; none were reported injured.

The fire had gone out by the time firemen arrived. Concerned that health hazards may have been posed by the chemical materials in the lab, responders switched to hazardous materials protocol and made sure the entire building was evacuated.

The Stanford Department of Public Safety closed Via Ortega and Serra Mall to traffic, reopening both streets at about 3:05 p.m.

“It probably wasn’t much of a fire,” Gibbs said. “More, a lot of smoke.”

Coincidentally, Allen had been scheduled for a test of its emergency horns and strobe lights between 6:30 a.m. to 7:30 a.m. Friday, and a silent test of its smoke detectors from 7:30 a.m. to 3 p.m. Gibbs said these tests would proceed as planned.

The lab, located at the northwest end of the first floor of the Allen building, is the James D. Fleming lab run by electrical engineering professor Jim Harris. Harris was not immediately available for comment on Thursday afternoon; it is unclear whether he was in the lab when the fire flared.

A sign on the door of the lab called the room the “Mostly Broken Equipment Lab,” a joke on the MEB equipment the lab houses. The equipment can difficult to maintain and clean, said Ed Myers, a science and engineering associate at the Stanford NanoFabrication Facility in the main CIS building.

The door sign also listed the names of seven people, including at least five Ph.D. students who work for Harris, some of whom appeared Thursday afternoon to be back in the lab “buttoning everything down,” according to Kevin Kinast of Environmental Health & Safety, who was also on the scene.

Myers said that the facility’s toxic gas monitoring systems are used by the adjacent annex, which is why he and others in CIS were alerted to the fire alarm and evacuated.

He said a large stainless steel chamber contained thin metal liners that lab researchers were cleaning on Thursday, a maintenance practice they do about every two years. Chemical residue from past experiments was being scrubbed away; just removed from a high-pressure vacuum, the residue may have oxidized and “energetically” released heat, Myers said.

It was an “exothermic reaction that kind of got away from them,” Myers added. “Students have a tendency to take risks.”

Some 150 people work in the CIS building and annex, according to a phone directory.

Environmental Health & Safety staff will review Thursday’s incident and recommend future safety protocols, Gibbs said.

Elizabeth Titus contributed to this report.