A concern faced by many oil and chemical companies is that, over time, process modifications or facility expansions, combined with increased population densities in surrounding communities, create the potential for a major accident with significant public impact. This paper will discuss the use of common risk assessment tools, along with the application of risk tolerance criteria, that can help in deciding if risks associated with the handling and storage of highly hazardous materials have become intolerable, requiring mitigation.

In this study, a novel portable electrostatic ground tester is developed, and its fundamental characteristics are experimentally discussed. An explosion test is also included in order to evaluate the ignitability of the novel tester under air that contains approximately 5.25 vol％ propane. The novel tester mainly consists of the ignition discharge suppression part with a contact electrode of 100 MΩ resistance, the connection part, and the voltage measurement part. The novel tester is based on a principle of a ratio between the voltage characteristics and the parallel connection of the internal capacitor （measured value: 1270 pF） with the capacitance of the object to be measured. As for the experimental results, if the metal object is not grounded, the voltage is displayed as a certain value. If the metal object is grounded, the voltage was immediately displayed as zero. Through several tests in this paper, the validity of the novel tester was confirmed. In addition, no ignition was observed with the novel tester （the electrode with values above 50 MΩ resistor）.

Flammable liquids with high flash point, such as kerosene, easily ignite when atomized, even at temperatures below their flash point. The measured ignition energies of these mists reported in previous studies vary widely, ranging from about 4 mJ to about 200 mJ. These differences in the measured values are thought to be caused by the measurement conditions such as mist particle size and concentration, but the relationship between these measurement conditions and the ignition energy has not been fully understood to date. In this study, the relationship between various conditions and the ignition energy of kerosene mist with a median diameter of approximately 5 μm was investigated using a minimum ignition energy measurement device for dusts （MIKE-3, Kühner AG）. As a result, it was confirmed that the concentration of the mist and the gap of the discharging electrodes had a significant effect on the ignition energy of the mist. It was also confirmed that the ignition energy was much lower （estimated to be less than 1 mJ） than the conventional data.