Despite a number of studies, the information about the multifaceted dangers associated with the manufacture, transport and storage of nanopowders remains insufficient and justifies the initiative of the NANOGRA project: Nano Global Risk Assessment. The latter aims at a multidisciplinary study (flammability and explosivity, toxicological and eco-toxicological risks) of potential risks related to nanomaterials and nanoparticles with prior economic interest in the Walloon Region. This paper discusses the experimental results of determination of the ignition sensitivity and explosivity characteristics of Carbon Black N990, Corax N550, MWCNT MC 700 and partially passivated metallic nanoparticles (Aluminum). Key information regarding MIE, Pmax and Kst values was obtained for carbon nanopowders. The results of the different tests have led to the conclusion that the carbon nanopowders are capable of generating an ATEX during suspension in the air, with moderate explosion intensity comparable to the ST1 class. They are little and not even sensitive to electrostatic phenomena. Generally, the assessment of explosion parameters of carbon nanopowders has been found to be similar to their microscopic size analogue. The pyrophoric nature of the partially passivated aluminum nanopowder required screening tests (e.g. MIT layer and combustibility) to control the risk of ignition in the steps of the characterization tests. In addition, against expectations, post-test hazards have been highlighted and required to somewhat adapt some tests protocols. The results show that aluminum nanoparticles are very sensitive to the risk of ignition by a phenomenon of electrostatic origin or self-heating, or friction mechanism event when partially passivated. For some aspects they exhibit expolsivity and flammabilyty risks significantly higher than their microscopic sized counterparts.