Hydrogen is a promising clean energy carrier to build a zero carbon society in future. The hydorgen reletaed technologies such as production, storage/transportation, and conversion to electricity have been rapidly progressed especially in recent years. However, hydrogen is known to be excellent combustible owing to wide flammable range, low minimum ignition energy, and significantly high laminar burning and propagation velocities, and also their flames are difficult to be observed by naked eyes, which carry a high risk of serious accidents. Given the hazardous characteristics, efficient combustion management techniques are required for safe operation of hydrogen. Hereby, we present the effect of carbon dioxide addition and mesh coverage on reduction of hydrogen fire risk. The results of experiments with a small slit burner emulating a crack such on hydrogen transportaion pipes clarified follows: （1） hydrogen diffusion flames can be visualized by carbon dixoide addition to hydrogen gas; （2） carbon dioxide addition to hydrogen gas causes flame instability, resulting in the change in flame shape and the reduction of flame size, eventually quenching with increase in the carbon dioxide proportion ; （3） coverrage of gas ejection port by fine metal meshes is effective for quenching. The combination of carbon dioxide addition and mesh coverage with optimal specification can become a better safety operation technique for hydrogen related technologies.

Kerosene is a flammable liquid with a high flash point, but it is easily ignited in mist form at room temperature, with a minimum ignition energy of less than 1 mJ. When an insulating liquid such as kerosene is strongly charged due to agitation or flow, an electrostatic discharge called brush discharge occurs between the liquid surface and nearby conductors. In recent years, there have been cases of fires in which kerosene mist was presumably ignited by brush discharge but the ignition hazard of this combination has not been studied. In this study, experiments were conducted using a simulated brush discharge generated between a metal sphere electrode and a PTFE plate by an external electric field as an ignition source to investigate the ignition hazard of kerosene mist by brush discharge. As a result, the risk of kerosene mist igniting by brush discharge is considered to be high, as ignition was confirmed in the experiment.