How is hydrogen autoignition an extrinsic property?

Hydrogen gas [henceforth mentioned as hydrogen] is widely utilized in industries; its accidental release poses a significant fire and explosion hazard. About 86.3 % of all hydrogen-related fires and explosions have no identifiable ignition sources, suggesting the potential of hydrogen undergoing spontaneous ignition. This phenomenon is hypothesized to be influenced by various environmental factors, including hot surfaces from industrial equipment, catalytic particulates such as iron oxides, inert particulates such as silica, and other external factors that reduce the autoignition temperature (AIT) and lower the minimum ignition energy (MIE). To address this gap, the present study developed a modified experimental apparatus based on the principle of ASTM E659-15 and Godbert-Greenwald (G-G) furnace to determine the AIT of hydrogen together with evaluating the effects of inert particulate (SiO 2 nanopowder), catalytic materials (Fe/Ni alloy and Fe 3 O 4 nanopowders) and obstructions/hot surfaces (steel mesh) on its spontaneous ignition. The experimental observations revealed a significant reduction in hydrogen's AIT by 1.22, 1.89, and 1.24 times in the presence of Fe 3 O 4 , Fe/Ni alloy, and SiO 2 nanopowder, respectively, through potential distinct mechanisms. Additionally, the position of steel mesh relative to its entry point into the test apparatus was observed to have a significant impact on hydrogen's minimum ignition temperature (MIT). In certain positions, steel mesh acted as both an obstruction and a localized hot surface and thereby reduced the MIT of hydrogen by a differential of 100 °C. These findings underscore the necessity of incorporating external risk factors into hydrogen safety assessments rather than relying solely on its inherent ignition properties (i.e., hydrogen autoignition may not be treated as an intrinsic property). A comprehensive approach that accounts for these environmental influences is essential for enhancing risk mitigation strategies in industrial hydrogen applications. • It investigates the discrepancies in hydrogen autoignition temperature and minimum ignition temperature. • It investigates the impact of external parameters on minimum ignition temperature and autoignition temperature. • The study observed a significant difference in the reported autoignition temperatures. • The study findings highlight the importance of external factors in assessing hydrogen fire risk.