Overpressure loading and structural damage in confined natural gas explosions: A 3D reconstruction-based fragmentation analysis

Natural gas explosions in confined spaces can cause severe structural damage, yet the quantitative relationship between overpressure loading and structural damage remains insufficiently understood. This work investigates the coupling between overpressure and window damage through five full scale confined natural gas explosion experiments with varying leakage positions and equivalence ratios. Internal overpressure histories were measured near a venting window, and characteristic parameters were extracted for the stages before and after vent opening. After each test, the post-explosion scene was reconstructed using a 3D reconstruction framework, and window fragments were identified for quantitative analysis. A volume-weighted average fragment displacement was introduced to characterize the spatial dispersion of damage. The results show that internal overpressure exhibits a two stage evolution. Increasing equivalence ratio accelerates pressure accumulation and intensifies the post opening pressure response, while leakage position has a limited influence before vent opening but significantly affects the post opening stage. Window damage evolves from localized failure to extensive fragmentation as explosion intensity increases, accompanied by an increase in fragment displacement and a reduction in the volume proportion of the largest fragment. Image processing results and 3D reconstruction results show consistent overall trends, but the latter provide more reliable quantitative characterization by reducing misidentification and preserving fragment geometry and spatial position. A quantitative relationship is established between overpressure loading and structural damage, with the vent opening parameters, especially the opening impulse, showing the strongest relationship with fragment dispersion. These findings provide a quantitative basis for explosion damage assessment in confined spaces.