Abstract Charcoal seems one of the most promising bio-reducer because of its high coke replacement ratio in blast furnaces. Nevertheless, biochar materials are subject self-combustion during storage, handling and transport, and need to be studied in order to understand and limit these phenomena. Heat-based methods: were employed to compare and determine the self-ignition parameters of four types of fresh biochar ( Quercus pubescens , Cyclobalanopsis glauca , and Trigonostemon huangmosun , Bambusa vulgar ) that are used as bio-reducers in the silica industry. This study assumed that spontaneous combustion arises from exothermic oxygen chemisorption to fresh biochar surface. Sample mass, heat flow and CO 2 desorption were measured. The weight increased very rapidly as soon as the gas stream was changed from N 2 to air accompanying the heat generation for each material. Desorption isotherms were found to depend on the nature of the feedstock confirming that bamboo biochar was the most reactive one under air exposure.