Small-flame response of Scots pine treated with two commercial fire-retardant impregnants: a comparative screening study

This study compared untreated Scots pine with wood treated using two commercial water-based fire-retardant impregnants at 230 g/m². Five specimens per group were exposed to a 20-mm burner flame for 30 s using a modified PN-EN ISO 11925-2:2020-09 procedure. Both treatments increased t150 from 10 s to 25 s and reduced mean maximum flame height from 212.8 mm in controls to 171.0 and 169.6 mm. Maximum flame height differed among groups (Kruskal–Wallis, p = 0.007). Glowing occurred in all controls after burner removal but in no treated specimens. Results indicate delayed early flame development under the applied screening conditions but do not support reaction-to-fire classification.