Pyrolysis is the cracking of material. In most cases, the cracking is done by heating the material at a high temperature (> 300°C) in the absence of oxygen. Cracking is unlike burning, which takes place in the presence of oxygen. A practical use of pyrolysis is the cleaning programs of some modern ovens that remove all burnt-on residues at approximately 500°C. Pyrolysis may also be applied to convert biomass in biofuels or for the cracking of polymers. The resulting products can then be separated with a GC system and be measured with a mass spectrometer (MS) or other detector. There are various types of pyrolysis units that each have their own specific features. Listed below is an overview of the various possibilities.