Hydrogen is expected as the next generation energy. However, there is concern that the serious fire and explosion accidents caused by the static electricity may happen because the minimum ignition energy of hydrogen is considerably small and its flammable range is very wide. Therefore we conducted a series of tests to investigate the electrification characteristics of the hydrogen spouting system when hydrogen leaks rapidly from the crack on plumbing with dust. Iron（ Ⅲ） oxide was used as the sample dust in the spouting system. The spouting system was separated electrically to the straight pipe part and the nozzle part, and the generated currents at each part were measured. As a result, the generated current at the nozzle was much larger than that at the straight pipe. Additionally, the quantity of the specific charge of the dust depended on the mass of iron oxide remaining at the inside of nozzle, and it suggested that the electrification at the nozzle greatly depended on the number of particles that can collide with the wall inside the nozzle.

The ignition energies and explosion limits for 15 solvent vapor／air mixtures were measured using a newly developed temperature─adjustable ignition test apparatus. For all the mixtures, the minimum ignition energies （MIEs） decreased exponentially, and the explosion limits expanded as the test temperature increased. The acetone vapor／air mixture, among others, depended strongly on the temperature─the MIE at 25 ℃ was less than one third that at 100 ℃. Empirical equations for estimating the upper and lower explosion limits by an electrostatic spark from those by a more energetic ac spark were derived. A mixture of acetone, water and air was effectively inactivated when the water concentration was 30 vol％ at 100 ℃.