The transition from low temperature carburisation to full flame is caused by the self-ignition of the pyrolysis gases on the not low temperature carburisation surface. A one-dimensional model is formulated to describe it. The self-ignition limits determined from this are in good agreement with the experimental results. The expected decisive effect of the incoming flow speed and therefore the heat transfer is confirmed. From the external ignition investigation on the spark section it was found that all resulting pyrolysis gas atmospheres are explosive, even if they do not always ignite at the low temperature carburisation furnace. (orig.)SIGLEAvailable from TIB Hannover: F93B347+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman