PROVIDENCE — A raging fire of suspicious origin Thursday afternoon destroyed the old carriage house of the former Gorham silver manufacturing plant off Elmwood Avenue that was being converted into a firefighters’ museum.

The carriage house, the last standing building of the industrial complex that once stretched over a 37-acre area between Mashapaug Pond and Adelaide Avenue in the Reservoir Triangle neighborhood, was being restored by Providence firefighters to turn it into the Providence Fire Museum.

“This is not good. It’s a real sad day,” said retired firefighter Tom Peckenham. He said members of Local 799, International Association of Fire Fighters, and other volunteers had put in “countless hours” since 2002 restoring the large brick edifice. The Providence Fire Department Historical Society had planned to fill the museum with memorabilia and fire apparatus going back more than a century including antique trucks that were used in the late 1880s.

First used by the silver manufacturer to keep horses and carriages, the carriage house was used by Gorham to store motorized vehicles and later used it as a company store.

What remains of the 115-year-old structure is likely to be demolished on Friday, after members of the arson squad conduct an investigation.

Three firefighters were taken to Rhode Island Hospital with minor injuries, said Battalion Chief Timothy McDaniel. He said the building was already engulfed in flames when firefighters arrived around 4:45 p.m., causing him to put out a second alarm.

“This is a killer,” said Jeffrey Herman, who worked as a silver designer at Gorham during the early 1980s and was a founder of the Society of American Silversmiths. “At the turn of the [20th] century, Gorham was the world’s leading manufacturer of silver products. This building was the last visible vestige of what once was.”

rdujardi@projo.com