Investigation Of Flame Spread Behaviors Of PU Insulation Materials Coupled With Building Exterior Wall Geometry

Organic insulation materials are widely used for building insulation purposed as the demand for energy saving buildings increased in recent years. Polyurethane is one of the typical organic insulation materials which is used worldwide in building insulation projects for its excellent insulation properties and low price. However, when not prop-erly treated, the use of polyurethane insulation material as well as other similar foam materials could lead to high fire hazard to buildings due to the high flammability nature of such foams. Besides, the building’s facade wall design was also considered as an im-portant factor that would influence the flame spread behaviors over insulation materials. The combustion characteristics and flame spread behaviors of polyurethane insulation materials are complex and influenced by many factors including sample properties, di-mensions, environmental parameters, geometrical configurations and so on. While a number of works involving some of the factors have been conducted, large amount of efforts are still needed to investigate those topics.The influence of sample width and ambient pressure on the horizontal flame spread over PU insulation materials were experimentally examined. Theoretical analysis on the flame spread mechanisms over PU insulation materials was presented. Tempera-ture profiles in solid and gas phase were obtained. Basic correlations between width and pressure changes and flame spread characteristic of polyurethane foams were ob-tained. It was found that The dimensionless flame height for horizontal flame spread was proportional to the sample width to the power of -n, regardless of pressure varia-tion. The mass loss rate was in positive power law relationship with both sample width and pressure. The flame spread rate followed a negative power law of sample width and a positive power law of pressure. Temperature profile analysis showed that the preheat zone could be divided into two zones:far field and near field. The differences between the two zones are that the effect of convection in far field is cooling effect, while that in near field is heating effect. Theoretical analysis on heat transfer on width and pressure effects was also provided. Good agreement of trends was found between experimental results and theoretical calculation.Two series of experiments were conducted to evaluate the influences of U-shape geometry and pressure on downward and upward flame spread over PU insulation mate-rial. Characteristic parameters such as flame spread rate, mass loss rate and flame height were investigated. Theoretical analysis were performed on both situations. Hypothesis models were proposed for U-shape geometry’s influences in both situations.For downward flame spread over U-shape geometry, it was found that the flame spread rate and mass loss rate increased while deceleration trends were observed with the increasing U-shape geometrical factor. The maximum increase for flame spread rate and mass loss rate between without and with sidewalls were approximately 20% and 40%, respectively. Averaged flame height increased slightly with geometrical fac-tor. Flame spread rate, flame height and mass loss rate were in positive relationships with ambient pressure. By providing an air entrainment analysis, it was found that, the-oretically, the downward flame spread rate over U-shape geometry was proportional to the induced flow speed which increased with geometrical factor and mass loss rate, and decreased with back wall width. The theoretical analysis was in good agreement with experimental results.For upward flame spread investigations, it was found that the U-shape wall had significant influences on upward flame spread. In both plain and plateau, the flame spread rate and the mass loss rate increase as the U-shape geometry becomes deeper. The time for flame to propagate a certain distance follows an exponential decreasing trend with upper and lower boundaries. It could be deducted that the upper and lower boundary indicated the time for the flame spread over a certain distance for flat shape configurations and infinity sidewall width geometry, respectively. This could be used to evaluate and predict the flame spread behavior of U-shape geometry. Moreover, the flame spread rate was much higher in plain than in plateau. Theoretical analysis showed that the key parameter was the upward flow induced by the air entrainment from bot-tom and front side of the geometry which enhances the heat feedback. Moreover, the strengthening of cooling effect of induced upward flow and the decreasing of combus-tion efficiency are the reasons for the lower boundary of the time for flame to propagate a certain distance.To evaluate the small scale model of U-shape geometry’s influences on the real ap-plication of upward flame spread over insulation materials,large scale experiments were conducted to investigate the fire hazard of building’s U-shape facade wall geometry. Comparison to laboratory scale experiments were presented. Theoretical analysis was validated through large scale results to reveal the mechanism of the U-shape geometry’s influences. Results showed that U-shape facade wall geometry design would increase the fire hazard of buildings:flame spread rate and flame height increased with geo-metrical factor. The time needed to spread a certain distance decreased exponentially with geometrical factor. The trend was similar to that for small scale experiments. The results agreed with the theoretical analysis.According to the results obtained in this thesis, the PU insulation material would have high fire hazard in real applications when the sample dimensions increase, not only for buildings’facade insulation situations. Moreover, buildings’U-shape facade wall geometry would greatly benefit flame spread for full scale applications. Thus would increase the fire hazard of such buildings. These results could be used in the evaluation of fire hazard and prediction of fire behaviors of polyurethane insulation materials. The results could also provide guidance for the safety designing of buildings.