Firefighters took seven hours to contain a blaze that ripped through the ground floor of a commercial building in Central yesterday, forcing the evacuation of hundreds of office workers. Two firemen suffered minor injuries. The fire was detected when smoke was seen billowing from beneath the shutter of a shop in the Prosperous Building, Des Voeux Road, at 7.24 am. The building managers had been ordered by the Fire Services Department to have a sprinkler system installed by next year. Firemen used welders to cut open the shutters and evacuated hundreds of workers from the building and nearby offices as the blaze was upgraded to a third-alarm fire at 8.37am. Fires are rated on a scale of one to five according to their seriousness. Parts of Des Voeux Road had to be sealed off as thick smoke blanketed the area and people on their way to work were kept away from their offices. Four teams of firefighters wearing breathing apparatus finally contained the fire at 1.41pm. A 47-year-old fireman who suffered smoke inhalation was in a stable condition in Queen Mary Hospital last night. Another fireman, 30, suffered minor back injuries and was discharged after being treated in hospital. The Fire Services Department said the fire was believed to have been caused by welding workers who accidentally set leather goods on fire. Thick smoke given off by burning leather made the fire difficult to put out, a department spokesman said.