A straight or curved length of steel, usually of H or channel section, used for support purposes in mine roadways, faces, or shafts. A steel support (1) possesses a high degree of permanency or long service; (2) ensures a minimum area of excavation for given dimensions in the clear; and (3) is fireproof. In return airways and shafts, a chromenickel- copper steel is sometimes used to counteract the corrosive air. For high-strength roof bars best results are obtained by the use of heat-treated low-alloy steels of the carbon manganese type.