An experimental study on the effect of equipment entrance area on explosion during deflagration of hydrogen-air mixture in a semi-confined space

This study experimentally investigated the explosion characteristics of hydrogen–air mixture deflagration in a full-scale L-shaped semi-confined concrete structure, focusing on the effects of the equipment-entrance area and ignition location. Increasing the entrance area substantially reduced the peak internal overpressure by up to approximately 2.6 times while external incident pressures showed localized increases attributable to horizontal dispersion. As the ignition location moved farther from the entrance, the peak overpressure increased markedly due to the extended flame-propagation path, enhanced turbulence generation, and complex pressure-wave reflections within the multi-compartment geometry. The external flame behavior also varied significantly with the test conditions, transitioning from a concentrated axial jet under small-entrance and front-ignition conditions to a wider mushroom-shaped flame for larger entrances and rear-ignition cases. Damage assessment based on overpressure–impulse criteria indicated that all test conditions fell within the “No harm (TTS)” to “Injury” range for human impact and within the “Minor structural damage” range for buildings, with neither fatality nor severe structural collapse predicted. Comparison with Molkov-based analytical correlations showed that, although the overall trends were consistent, the correlations tended to underpredict the measured peak overpressures, suggesting that single-compartment vented-deflagration models may have limitations when applied to multi-compartment configurations.