A hydrocarbon conversion process such as an auto-thermal cracking process in which a hydrocarbon feed and a molecular oxygen-containing gas are contacted in a reaction zone in the presence of a catalyst to produce an outlet stream having an oxygen concentration which is at, near or above the flammable limit and in which process a loss of reaction is detected and used as a signal to activate means for mitigating the risk of explosion downstream of the reaction zone. The loss of reaction may be detected for example by a sudden increase in oxygen concentration in the outlet stream and/or a sudden drop in temperature of the outlet stream.