The blaze started about 10 a.m. when the gasoline tank of a vehicle being serviced at Fellsway Auto caught fire, said Somerville Fire Chief Kevin Kelleher.
As the department received multiple reports of the blaze, located on a busy thoroughfare, Somerville Police Officer Michael Wyatt was passing the area in his cruiser when he said he saw smoke.
"I heard a bunch of people screaming," said Wyatt, a 25-year police veteran. "As I approached someone said there was someone still inside."
Wyatt said he rushed to the rear of the one-story business, along with another man, and pulled one shop worker through the gap in a louvered window.
The other worker couldn't fit through the space so Wyatt broke through the glass with his baton to make room, he said in an interview after the fire.
"[The employee] said the smoke was so thick he couldn't get to the door," Wyatt said.
Fire Chief Kevin Kelleher said four Fellsway Auto employees were transported to Massachusetts General Hospital for minor burns and smoke inhalation. Their injuries are believed to be non life-threatening, Kelleher said.
Kelliher said crews arriving on scene encountered thick plumes of black smoke, likely generated from the chemicals, plastics, and accelerants naturally found in an automotive repair shop.
The building, at 693 McGrath Highway, was a total loss, Kelleher said. He declined to estimate the cost of the damages. The property is valued at more than $640,000, according to city tax records.