Hydrogen energy is pivotal in the energy transition due to its high efficiency and zero-emission characteristics. However

the potential for explosions constrains its broader application. Gaining insights into the dynamics of overpressure in hydrogen explosions is vital for the safe design of explosion-proof facilities and the determination of equipment spacing. This study investigates hydrogen explosions in open spaces of 1 and 27 m3 volumes

analyzing flame propagation and overpressure distribution. It also evaluates the accuracy of three theoretical models in predicting peak overpressure. The results reveal that the spherical flame from a hydrogen cloud explosion transforms into an ellipsoidal shape upon contact with the ground. The average flame propagation velocity across different equivalent ratio is ordered as follows: Va (φ = 1.0) > Va (φ = 1.5) > Va (φ = 2.5) > Va (φ = 0.5). At equivalent distances

the peak overpressure of hydrogen cloud explosions is comparable across both scales. The traditional trinitrotoluene model overestimates the peak overpressure of hydrogen cloud explosions at both scales. The optimized trinitrotoluene model achieves over 90% accuracy in predicting hydrogen cloud explosions in 1 m3 volumes but shows decreased accuracy in 27 m3 explosions. At source intensity level 3

the Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek multi-energy model exhibits a prediction accuracy of over 70% for peak overpressure in hydrogen cloud explosions

with consistent performance across different scales

rendering it a more reliable model for such predictions. This research enhances hydrogen safety assessment technologies by providing a more precise method for evaluating large-scale hydrogen cloud explosion risks.