Journal of Occupational Safety and Health
Online ISSN : 1883-678X
Print ISSN : 1882-6822
ISSN-L : 1882-6822
Advance online publication
Displaying 1-3 of 3 articles from this issue
  • -Estimation of Tsi based on oxidation temperature rise rate of ARC-
    Yeongsoo CHOI, Kouya MURAI
    Article type: original article
    Article ID: JOSH-2023-0020-GE
    Published: June 26, 2024
    Advance online publication: June 26, 2024

    To assess the risk of spontaneous ignition in the utilization of fine powdered coal within a plant, we conducted an examination of exothermic onset temperature and calorific value using High Pressure Differential Scanning Calorimetry (HP-DSC). Additionally, the induction time of the fine powdered coal was investigated using the Spontaneous Ignition Tester (SIT), and the Time to Maximum Rate at adiabatic condition (TMRad) was determined using Accelerating Rate Calorimetry (ARC). Based on the SIT and ARC results, it was observed that if there are hot spots within the fine powdered coal under adiabatic conditions, thermal runaway could occur within a few minutes due to the exothermic oxidation reaction, indicating a high risk of fire during abnormal conditions.

    As a new approach to estimating the Self-Ignition Temperature (Tsi), simulations were conducted using ARC data for the oxidation temperature rising rate. The results indicated that the Tsi is estimated to be 314 K at a drum scale of about 200 L, suggesting the potential for spontaneous ignition, particularly during the summer season. We believe that the estimation of Tsi by this method can be applied to other substances prone to spontaneous ignition as well.

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  • Natsuko WASAKI, Akiko TAKAHASHI
    Article type: original article
    Article ID: JOSH-2023-0016-GE
    Published: May 09, 2024
    Advance online publication: May 09, 2024

    Inattentiveness is a human trait that cannot be entirely avoided. However, even minor lapses can result in significant accidents. This study aimed to elucidate the characteristics of occupational accidents stemming from inattention. A total of 31,496 cases of occupational accidents occurring in 2017 were analyzed. Individual cases suspected to be caused by inattention were classified based on industry, accident type, age, context, type of inattention, and targets that should have been attended to. Consequently, we found that, first, fall accidents were largely attributed to inattention. Second, accidents caused by inattention tended to increase with age. Third, inattention on occupational accidents was caused mainly by the limitation of attentional capacity rather than that of sustained attention. Fourth, the context and target regarding occupational accidents caused by inattention were industry-specific. Accordingly, we emphasize the importance of understanding the characteristics of inattention in the workplace and propose safety measures based on the results.

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  • Kwangseok CHOI, Yuta ENDO, Yusuke SUZUKI, Kenzo YANAGIDA, Kenichiro SH ...
    Article type: brief report
    Article ID: JOSH-2023-0017-TA
    Published: May 09, 2024
    Advance online publication: May 09, 2024

    In this paper, the incendivity of abnormal discharges occurring from an electrostatic powder coating gun was experimentally examined using two methods (i.e., transferred charge amount measurement test and explosion test). In the whole experiments, the discharge gap (the distance between the nozzle tip and the grounded electrode) was kept constant at 10 mm, and a methane-air mixture gas (12.0%) was used as the test gas in the explosion test. As for the results, under all experimental conditions, abnormal discharge did not occur when the Over Current Limit (OCL), which is the safety device of the electrostatic spray gun, was enabled. When the OCL was released, the absolute value of the transferred charge amount was 70 nC or less when the setting value of the current control device was -80 μA and -110 μA. There were no ignitions under these conditions. On the other hand, when the set value was -120 μA, -130 μA and -140 μA , the absolute value of the transferred charge amount was 1,500 nC or more. There were ignitions because the transferred charge amount greatly exceeded the ignition risk threshold value of 200 nC (absolute value) mentioned in EN50050-2. As described above, since a clear correlation was confirmed between the transferred charge amount measurement test and the explosion test, the ignition risk can be evaluated by grasping the transferred charge amount in advance.

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