First they felt their boots stick to the linoleum tiles. Then the firefighters started to feel the plastic on their protective masks break down. The next room over had just flashed with an explosion, and they believed theirs was next.

“They knew the warning signs for a ‘flash-over’ from their training, so they knew to get out of there,’’ said Auburn Assistant Fire Chief Glenn Johnson.

When two of his firefighters arrived at the four-alarm blaze in Oxford Monday at 2 a.m., it was unclear if everyone had been evacuated from the building. The two firefighters began to search the Main Street apartments above the burning salon, Shagged Hair Design, for anyone trapped inside.

But while in the upstairs units, the firefighters saw the telltale signs of a “flash-over,’’ Johnson said, and the crew issued a mayday call.

The “odd layout’’ of the apartment and low visibility caused two firefighters to become “disoriented,’’ he said. Thick smoke filled the dwelling, and the crew got lost.

The two firefighters, whose names have not yet been released, broke a window to escape the apartment and jumped onto the roof of the ­salon, officials said.

“They dove head-first,’’ Johnson said.

They were not injured. After leaving the building, the pair continued to fight the fire from outside, Oxford Fire Department Chief Sheri Bemis said

Before firefighters arrived at the building, the only two known occupants had been evacuated by a police officer and an unknown person who had driven by the blaze, Oxford Fire Department Captain Ken Sellers said.

They had no reported injuries, officials said.

Earlier that night, a driver saw flames and smoke coming from the salon and started beeping the car’s horn in an attempt to wake any occupants while he or she called 911, Bemis said. Officials could not confirm if the driver who made the 911 call was the same person who helped evacuate the building.

“Nobody seems to know who it is,’’ Sellers said.

More than a dozen emergency agencies from the towns surrounding Oxford responded to the fire at the three-story building, he said.

“We chased the fire for quite some time, but finally had it knocked down around 4 a.m.,’’ Bemis said.

Vicky Durant, who owns Shagged Hair Design, said that when her landlord called her at 2:30 a.m., she rushed to the scene to find her salon in cinders.

“There is nothing there, it’s a total loss,’’ Durant said Monday afternoon, before she drove off to look for a new location for Shagged Hair Design.

The fire was not considered suspicious in nature, officials said. The cause was likely electrical and began in the salon, Bemis said.

Maddie Kilgannon can be reached at maddie.kilgannon@globe.com. Follow her on Twitter @MaddieKilgannon.