AMHERST — A smoke detector covered in plastic in a University of Massachusetts dormitory room, delaying firefighter response and evacuation of the building during a fire that started in a trash can and spread to a bed Wednesday evening, is prompting a criminal complaint for tampering with a fire alarm against the student tenant, according to the Amherst Fire Department.

Fire Chief Lindsay Stromgren said Amherst firefighters responded to McNamara residence hall in the Sylvan Residential Area on Eastman Lane at 8:02 p.m., after receiving a 911 call from a passer-by who saw smoke coming from a fourth-floor window of the eight-story, suite-style building.

An alarm was sounded for all on- and off-duty Amherst firefighters, with the crews initially arriving encountering moderate smoke on the fourth floor and able to quickly extinguish the fire, then spending an hour ventilating the building. All eight floors were evacuated, with tenants on all but the fourth floor able to return within 30 minutes, with others getting back after an hour. There were no injuries to residents or firefighters, Stromgren said.

An investigation revealed that a trash can fire moved to a bed inside the room, part of a multi-room suite. That room is not habitable at this time.

Fire investigators from the Amherst Fire Department, UMass Police Department, and the State Fire Marshal’s Office determined that the likely cause of the fire was careless disposal of smoking materials, even though smoking of any products is prohibited throughout campus.

The smoke detector in the fire room had been covered by plastic, making it inoperable during the fire and delaying the detection of the fire and evacuation of the building. A fire alarm was activated and pulled by a resident who saw smoke in the hallway.

In addition to the criminal complaint, the student is expected to face university charges under the Student Code of Conduct.