Students stood on the sidewalk outside the College of Engineering building at 44 Cummington St. for about 35 minutes Wednesday afternoon, shivering in the heavily falling snow and rain, while firefighters searched the building for the source of a mysterious burning smell. The source of the smell was never discovered, and firefighters deemed the building safe.

The Boston Fire Department responded to a call reporting the scent of smoke in the building at about 2:30 p.m. and arrived on the scene less than three minutes later, Deputy Fire Chief Richard Dunderdale said. By the time firefighters cleared the building, six fire trucks, a rescue unit and multiple Boston University Police Department cruisers were parked outside the building.

Students working in the labs inside the building had noticed the smoky smell for about an hour before any action was taken. ‘We were smelling it, and our lab instructor thought it was coming from the fume hood,’ Cara Sarrel, a first-year graduate student in ENG who was working on the fifth floor when the fire alarm was activated, said. ‘But there was nothing in the fume hood.’

When the fire department arrived, they pulled the building’s fire alarms to prompt students to evacuate.

‘We didn’t hear the alarm, so someone actually came in and got us,’ Sarrel said. She also said someone spoke over the intercom after alarms began sounding to doubly urge everyone to leave the building.

Sonaly Mahalanavis, a post-doctoral student in ENG said she had not yet responded to the alarm when firefighters came to the door of the room where she was working and escorted her and her classmates out.

‘I was curious as to why I was smelling smoke,’ she said, ‘But I didn’t see anything in the hallway or where I was, so I just stayed put.’

Dunderdale said the firefighters, about 35 of whom entered the building, checked the third through eighth floors looking for the source of the smell.

‘We’re checking all the electrical systems to see if that’s it,’ he said as he waited outside the building with the evacuated students. ‘All our companies are up there with thermal imagers looking for hot spots. We’ll look at all the ceilings, elevator rooms, anywhere we need to look, and hopefully we’ll be able to locate it quickly.’

After the firefighters cleared the building, Dunderdale said that the source of the smell had not been found.

‘The odor dissipated, so we never found the source,’ he said. ‘We didn’t find the exact location, but we’re confident that the problem’s alleviated.’

He said that the smell could have come from an overheated motor in the building.

Also on the scene were BUPD officers, who stood at the doors of the building, barring students from reentering. BU Physical Plant employees also stood by in case the problem was with the heating system, said Physical Plant employee Bob Guanci, who was told to leave the building when he tried to enter.

‘I went in there and waited to find out if there was anything we needed to do,’ Guanci said, standing back from the firefighters.

BFD Spokesman Steve McDonald said that since the building housed laboratories and potentially volatile projects, the firefighters took extra care in searching for the smell.

‘You always confer with the lab personnel, and just go over what they’re working on,’ he said. ‘When you work with labs, you always go a little slower and have to use a little more caution.’

Daily Free Press staff writers Ellie Choi and Taylor Miles contributed reporting to this article.