Effects of miscrete moisture-containing material on the smoldering and the transition from smoldering to flaming combustion

In this paper,we have done experiments with a variety of kinds of fuel,including continuous samples,some of which are dry while others of which are wet,and discrete samples,also some of which are dry while others of which are wet.The goal of our studies is to find the effect of the discrete moisture-containing materials on the smoldering and the transition from smoldering to flaming combustion. As is known,the polyurethane foam is a common fuel in smoldering fire safety.Our experiments were arranged in a sequence from the dry materials to wet ones when they were smoldering and propagating along the samples.We used materials with different moisture contents in different experiments so that we can find different phenomena from the different experiments.In addition,we have recorded temperature histories in the smoldering process by using thermocouples. For the continuous combustion samples,when the moisture content of the wet part was below 7.4%,the smoldering propagation would be considered steady.However,if the moisture content of the wet part was between 10.3%-13.8%,the gas-phase reaction would take place and the transition to flaming combustion can be predicted. Furthermore,when the moisture content of the latter wet part reached 17.4%,there would be no flaming combustion appearing at all. Moreover,when the moisture content exceeded 20.9 %,the propagation of smoldering would be slowing down and extinguished.On the other hand,for discrete samples,the transition to flaming combustion would hardly take place at all.Nevertheless,when the moisture content of the latter discrete part reached 17.4%,the smoldering would be extinguished.Thermal analysis experiment of the polyurethane foam let us see that the TG and DSC data could clearly reveal the temperature scopes and characters of smoldering reactions.When the temperature scope remains between 250 _ 290 ℃,the reaction of the foam would be endothermic and then would release a lot of combustible gas while the TG curve would drop down quickly.At the scope of about 290-380℃,the reaction would be exothermic foam oxidation with a great deal of combustible gas produced.And,later, at the scope about 475-610 ℃,the reaction would be exothermic char oxidation.The heat transfer from the inner smoldering sample has also been analyzed.Such kind of heat transfer from the dry material to the wet one in continuous sample proves greater than that in the discrete samples.So the continuous samples tend to be more likely to smoldering propagation and transition to flaming combustion as compared with discrete samples.