Using ISO 19881 Annex E Guide Values as External References to Support ISO / IEC 17025 Accreditation of UN ECE R134 Chap. 5.4 and Annex 3 Part 5 Fire Tests for Hydrogen Vehicle Fuel Containers

Accreditation of fire testing laboratories under ISO/IEC 17025 commonly relies on proficiency testing or interlaboratory comparisons (ILCs). For UN ECE R134 §5.4 fire tests on gaseous hydrogen vehicle fuel containers, no ILCs are currently available. We evaluate the feasibility of using the guide values provided in Annex E of ISO 19881—derived from published reference testing—as external references to demonstrate method performance. Six ECE R134 calibration‐tank tests were conducted at Efectis; four compliant tests were retained for analysis. For the six required temperature metrics (localized and engulfing fire phases; burner‐side, opposite‐side, and worst‐case surface temperatures), 60 s means were computed within defined steady‐state plateaus. Assuming normality, equality‐of‐variance (Fisher F ‐tests) and equality‐of‐means (Student t ‐tests) were performed at 95% confidence between Efectis results and ISO 19881 Annex E data. Means were statistically equivalent across all metrics, while the Efectis dataset showed substantially lower variance—particularly for opposite‐side measurements. Repeatability ( s r ), estimated from four in‐house repeats, ranged 4%–11% for localized fire and 2%–18% for engulfing fire. Reproducibility ( s R ), estimated from the pooled ISO‐plus‐Efectis data, ranged 32%–55% and 15%–47% for localized and engulfing phases, respectively. These findings indicate that Annex E guide values can credibly underpin uncertainty statements and performance claims where formal ILCs are lacking, thereby supporting ISO/IEC 17025 accreditation pathways for ECE R134 §5.4 fire testing. Limitations, uncertainty budgeting, and recommendations for future community intercomparisons are discussed. The discussion also shows that a complete characterization of fire‐test severity should include HRR/A in addition to temperature‐based acceptance criteria.