Quantitative risk assessment using a Japanese hydrogen refueling station model

Although hydrogen refueling stations (HRSs) are becoming widespread across Japan and are essential for the operation of fuel cell vehicles, they present potential hazards. A large number of accidents such as explosions or fires have been reported, rendering it necessary to conduct a number of qualitative and quantitative risk assessments for HRSs. Current safety codes and technical standards related to Japanese HRSs have been established based on the results of a qualitative risk assessment and quantitative effectiveness validation of safety measures over ten years ago. In the last decade, there has been much development in the technologies of the components or facilities used in domestic HRSs and much operational experience as well as knowledge to use hydrogen in HRSs safely have been gained through years of commercial operation. The purpose of the present study is to conduct a quantitative risk assessment (QRA) of the latest HRS model representing Japanese HRSs with the most current information and to identify the most significant scenarios that pose the greatest risks to the physical surroundings in the HRS model. The results of the QRA show that the risk contours of 10^?3 and 10^?4 per year were confined within the HRS boundaries, whereas the risk contours of 10^?5 and 10^?6 per year are still present outside the HRS. Comparing the breakdown of the individual risks (IRs) at the risk ranking points, we conclude that the risk of jet fire demonstrates the highest contribution to the risks at all of the risk ranking points and outside the station. To reduce these risks and confine the risk contour of 10^?6 per year within the HRS boundaries, it is necessary to consider risk mitigation measures for jet fires.     

Photoluminescence enhancement by isolating β-FeSi2 layers from defective layers

We have investigated an optimal annealing process in order to enhance 1.55 μm light emission from semiconducting β-FeSi₂ and found that two steps annealing at 600 °C and 800 °C is effective to its enhancement. Rutherford backscattering spectroscopy and SEM observations revealed that pronounced surface segregation of Fe atoms during annealing at 600 °C caused surface precipitate of β-FeSi₂. The enhancement of light emission is attributed spatial isolation of the surface β-FeSi₂ (light emitting layer) from damaged and defective layers with nonradiative recombination centers.     

Relationship between office workers’ staying and workstation attributes in a non-territorial office using ultra wide band sensor network

This paper investigates the staying and moving characteristics of office workers in a non-territorial office using an ultra wide band (UWB) impulse radio sensor network. The differences between office workers’ staying and moving are clarified according to the individual workstation type that they select. The study determines the characteristics of each type of workstation. By clarifying office workers’ preference for staying and moving with regard to individual workstation types and office worker post, the reasons why office workers in different posts tended to select different types of workstations were revealed. Specifically, leaders tended to select workstations at the “inner meeting corner side” most frequently, as they had a greater need to stay in other areas. In contrast, ordinary staff needed to visit office workers in other areas less often, and as such, they tended to select individual workstations at the “middle meeting corner side.” Barring this, they tended to select individual workstations at the “middle corridor side” or “outer-meeting corner side.” Temporary staff members had little need to visit or stay at other places so they tended to select individual workstations at the “window side,” which is seldom visited or stayed at by other office workers and they could be disturbed less often from their solo work.     

Combustion Characteristics of Ammonium Nitrate and Carbon Mixtures Based on a Thermal Decomposition Mechanism

In order to obtain a better understanding of the combustion characteristics of ammonium nitrate (AN) and carbon (C) mixtures (AN/C), burning tests and differential scanning calorimetry (DSC) were performed. AN mixed with carbon that is oxidized by nitric acid (HNO₃), such as activated carbon (AC), burned at 1 MPa. However, AN mixed with carbon that is not oxidized by HNO₃, such as graphite, did not burn under 7 MPa. Compositions with more than stoichiometric amounts of activated carbon had higher burning rates. Heat characteristic examinations found a similar trend. The burning rate of AN/AC mixed with CuO as a combustion catalyst deteriorated faster than an additive‐free one. From the DSC result, AN/AC/CuO had a higher onset temperature and a lower heat of reaction than AN/AC. These results suggested that, in the combustion wave of AN/C, a thermal decomposition zone is formed on the burning surface, and combustion performance was affected by the thermal decomposition of AN/C.     

The decomposition pathways of ammonium dinitramide on the basis of ab initio calculations

Quantum chemistry calculations incorporating solvent effects were used to investigate the decomposition pathways in molten Ammonium dinitramide (ADN). Optimized structures for reactants and products were obtained at the CBS-QB3//ωB97XD/6–311++G(d,p)/SCRF = (solvent = water) level of theory, considering the isomers ADN_I (NH₄–N(NO₂)₂) and ADN_II (NH₄–ON(O)NNO₂) and the four ADN_II conformers, which are minimal clusters of anion and cation in molten ADN. In the initial stage of decomposition, the ADN_II decomposes to NO₂? and NNO₂NH₄. Following the initial decomposition, NNO₂NH₄? decomposes to N₂O, NH₃, and OH?, and the OH? combines NO₂? to yield HNO₃. This decomposition can be written using one global formula: ADN → N₂O + NH₄NO₃ (NH₃ + HNO₃).