Study on the Effect of Moisture on Smoldering Propagation and Occurrence of Gas-phase Oxidation

Polyurethane foam, whose lower part remained dry and upper part was watered, was used in experiments to study the propagation of smoldering and its variation of reaction. Smoldering spread upward from the dry to the wet in natural convection. In experiments, the moisture contents of the upper samples were from 8.4% to 21.7%, and smoldering kept steady in the lower dry samples. Because of the endothermic evaporation of water, the state of smoldering varied greatly with the moisture content after it reached the sample interface of the dry and the wet. When the moisture content was low, smoldering continued, but its temperature and velocity somewhat decreased. With the increment of moisture content, smoldering reaction was suppressed. And the oxygen, which was not consumed completely by heterogeneous reaction, would react with the combustible gases and led to the occurrence of the gas-phase oxidation. While the moisture content was high enough, smoldering extinguished. In experiments, if smoldering propagated to the end, the transition to flaming combustion would occur for plenty of outer oxygen entering the reaction zone.