The fire at the MMK plant in the city of Magnitogorsk in the Urals broke out in a rolling section on November 28, and engulfed an area of about 1,200 square meters (13,000 sq feet).
The blaze continued until the following day, as firefighting efforts were complicated by fallen parts of the roof.
Eight workers were hospitalized, and several people were trapped in the facility when 3,600 square meters (13,000 sq feet) of the roof collapsed due to extremely high temperatures.
It was initially reported that 14 people were working at the facility's pickling section, which deals with acids, at the time the fire broke out, but officials suspect the number could be as high as 16.
About 500 rescuers are removing the debris, the spokesman said.
MMK managers earlier said the lives of the workers being treated in hospital are not in danger.
The results of investigations into the cause of the blaze have not yet been reported.
