Abstract
The Hydrogen Incidents and Accidents Database (HIAD) includes events initiated within hydrogen equipment, within a system that also contains hydrogen, or in a non-hydrogen system. This study characterized associations between the curator-assigned initiating system category and seven structured descriptors and multi-label root cause classes in HIAD 2.4. Analyses retained the original HIAD categories and used contingency-table tests, Cramér’s V, adjusted standardized residuals, Holm adjustment, and multinomial models. Of 1235 records with a known initiating system category, 825 (66.8%) were classified as hydrogen system-initiated, 99 (8.0%) as hydrogen-containing system-initiated, and 311 (25.2%) as non-hydrogen system-initiated. The largest associations were observed for initiating cause (V = 0.525) and supply chain stage (V = 0.492). Hydrogen-containing system records were most frequently classified in process-gas service (77.8%) and rupture with ignition (62.6%), whereas non-hydrogen system records more frequently involved unintended chemical hydrogen generation, impact/rollover/crash, no hydrogen release, and near misses. Material/manufacturing, installation, and job-factor labels were associated with lower adjusted odds of non-hydrogen-system versus hydrogen-system initiation. Associations generally persisted in higher-quality and post-2000 subsets. Because the compared fields were assigned by the same curators from the same narratives, the findings indicate within-database profile separation rather than the independent validation of incident mechanisms or accident rate estimation.