Fire testing of intumescent coatings : comparison between bench-scale furnace and radiant panels experimental methodologies

This study describes an experimental investigation on the fire performance of intumescent coatings using two different bench-scale experimental methodologies. Steel plates with and without a commercially available thin-intumescent coating were tested using a 26 dm3 propane-fired furnace or an array of natural-gas-fired radiant panels in accordance with the Heat-Transfer Rate Inducing System (H-TRIS) test method. Research outcomes demonstrate how the two bench-scale experimental methodologies can be adopted to effectively research and develop intumescent coatings for a range of equivalent thermal exposures. A comprehensive comparative analysis between the two methods was performed based on the transient swelling behaviour of the intumescent coating and the temperature of the steel substrate. The H-TRIS test method imposes well-defined and stable thermal conditions at the exposed surface of the swelling intumescent coating, while the mixed convective-radiative thermal conditions inside the bench-scale furnace occur over the whole coating surface, and their distribution and homogeneity are difficult to quantify in practice. Also, at high temperatures, the turbulent flow fields inside the furnace affected the coating degradation, showing detachment (partial or total, gradual, or sudden) of the swelled char and generating increased uncertainty of the thermal and physical conditions, but reproducing scenarios more realistic and similar to real compartment fires. Lastly, the H-TRIS test method allows for the measurement of the transient coating swelling during heating, but also exposed the tested samples to higher oxygen concentrations than those tested inside the furnace