Fire Chief Mike Jones told the Pilot-Tribune the apartment's resident had been smoking in bed about an hour before fire alarms were triggered.
"He was really lucky," Jones said.
No injuries were reported.
As a handful of evacuated residents watched from a safe distance, firefighters carried out and extinguished a smoldering mattress in front of the building, later returning inside to ventilate the upstairs apartment.
While fire damage was limited to the mattress, smoke damage was prevalent throughout the apartment, Jones said.
The building is owned by Dave and Ruth Peterson.