In the past years, the use of biomass has significantly increased and, therefore, so has the number of accidents related to its storage, transport, and use. To prevent these accidents, it is essential to properly know their flammability and explosion characteristics so their behaviour can be addressed as a first stop for preventing accidents. The present work studies the inertization with solid inerts of biomass layers and clouds (biomass powder suspended in air) as a possible solution to reduce their ignition tendency. To do so, two biomass samples were studied: wood pellets and dried sewage sludge; mixed with two different inert materials: recycled glass and sodium bicarbonate. In particular, the inert materials were mixed with biomass at three different concentrations (30%, 50% and 70%) and the ignition of the mixtures was studied, determining the minimum ignition temperature of layer and cloud (MITL and MITC) for each mixture, and detecting the needed concentration for avoiding the ignition. Additionally, samples were tested using TGA and DSC techniques to analyse their thermal behaviour and to determine the influence that the inert material has in the energetic power of the biofuel. Different behaviours were observed depending on the different inert materials, showing that not only the amount of inert added is important but also its physico-chemical properties. If the results for a layer and a cloud are compared, it was noticed that inertization effect differs between biomass and test. Regarding TGA and DSC results, it was concluded that smaller percentages of inert material should be considered, as they substantially modify the energetic value. •Inertization showed differences when testing different biomasses but also when addressing MITc and MITL.•When igniting the cloud, the heat transfer mechanisms are more evenly distributed.•Recycled glass provided a better inertization in MITc than sodium bicarbonate.•Physico-chemical properties of the inert materials played a significant role.