The Effect of Sample Size on Smoldering and the Transition to Flaming Combustion

Smoldering experiments and thermal analysis experiment were conducted to investigate the characteristics of smoldering maintenance and heat release. Polyurethane foam samples with different width were used in experiments and temperature histories were recorded. Smoldering just self-sustained and typically propagated to the end in natural convection as the sample width was 10cm. When sample width was less than 10cm, smoldering gradually quenched after ignited by cigarette. When sample width was larger than 10cm, smoldering propagated forwards with peak temperature gradually promoting to higher value, even transition from smoldering to flaming. TG and DSC analysis showed that heat released by solid reaction reached its high value at temperature scope of 400 - 500°C, rapidly decreased as temperature less than 400°C, and turned to be zero as temperature higher than 620°C. The analysis and result could well explain the phenomena in smoldering propagation, extinguishment, and transition to flaming combustion.