Developed by Albert Steiner in the 1940s, the Steiner Tunnel is a steel box lined on its sides and floor with fire brick and featuring a removable lid. The tunnel contains a 12-in. high fire chamber with two burners at one end providing 89kW of energy. The Steiner Tunnel was adopted as an ASTM Standard in 1950 and given the designation of E-84. The FSI and SDI indices are used to establish a scale for the rate at which flame spreads and smoke develops during an E84 test.