Members of the public rarely get to see what goes on behind the doors of the huge heavy engineering firm where huge steel castings, forging, ingots and bars roll off the production line each day.
Its hot and humid work - and our photographer Marisa Cashill was given a chance to see what goes on in the white hot furnaces of the plant which was founded in 1805.
Established in 1983 from the merger of Firth Brown and British Steel Corporation's River Don Works, the company can trace its heritage back to the start of the steel industry in Sheffield in the 18th century.
The factory has the capacity for pouring the largest single casting (570 tonnes) in Europe.
The two forging presses in use can exert a pressure of 3,500 tonnes and 10,000 tonnes on a billet of steel. The 3,500 tonne press was installed in 2010 to replace a 1,500 tonne press which dated back to 1897 and was originally steam powered, and after several upgrades became hydraulically operated.