The forced convection pit-type furnaces of the SAL series can be upgraded by the use of gas tight retorts for processes with defined atmospheres. These systems are very well suited for the heat treatment of bulk materials. By means of an additional retort and cooling station, the retort can be removed after completion of the heat treatment process and cooled in a cooling station. In the case of sensitive components, further flushing with protective gas can also be carried out during the cooling phase. The cooling station can be designed with or without forced cooling by means of a powerful fan. When equipped with a vacuum pump, the retort is evacuated outside the furnace in cold state and then flushed with protective gas. This procedure is particularly suitable for heat treatment of bulk solids as well as for non-ferrous and precious metals. Residual oxygen is much better and faster removed by means of pre-evacuation. Up to a maximum working temperature of 600 °C, the furnaces can also be operated under vacuum by connecting a vacuum pump depending on the type of pump, a vacuum of up to 10^‑5 mbar can be achieved. The furnaces can be equipped with gas supply systems for non-flammable protective and reaction gases. A gas supply system for operation under hydrogen, including safety technology, is also available as an additional equipment.