Fire behavior of thermally modified pine (<i>Pinus sylvestris</i>) treated with DMDHEU and flame retardants: from small scale to SBI tests

Abstract In this study, thermally modified Scots pine ( Pinus sylvestris L.) was impregnated with DMDHEU (1,3-dimethylol-4,5-dihydroxyethyleneurea) monomers combined with a flame retardant (FR) based on monoguanidine phosphate salt. Fire performance was assessed using ignitability tests (ISO 11925-2, 2020), mass loss calorimetry test (ISO 13927, 2015), and single burning item (SBI) tests (EN 13823, 2020). Results showed enhanced flame retardancy, reaching Class B in the SBI test. Small-scale ignitability tests revealed minor differences in flame spread across samples, unlike the SBI results. Fire growth rate and ignition time from mass loss calorimetry strongly correlated with burning suppression in the SBI test.