Fire Properties Of Commonly Used Organic Exterior Insulation Systems

In recent years, the "energy-saving policy" from the government has greatly prompted the application of a variety of organic exterior wall insulation systems in buildings. On one hand the effect on energy-saving efficiency has been significantly increased, but on the other hand the corresponding fire prevention codes lags far behind. A lot of combustible and flammable wall insulation materials have been used in exterior walls. As a result, the exterior wall fire accident occurs occasionally which threaten people’s safety of life and wealth. Although the No.56Decree of Fire Department of Ministry of Public Security strictly limited the use of combustible wall insulation materials, but a large number of organic insulation systems had been installed on the exterior wall which resulting in a significant fire hazards. Therefore, the study of fire properties of commonly used organic exterior insulation systems has become more important.Based on the statistics of the production and application of exterior wall insulation systems in Shandong province, the insulation systems studied in this paper can be grouped into four categories. They are the thin-plastering exterior insulation system (thin-plastering system), the exterior thermal insulation system with ceramic tile face (ceramic face system), the composited exterior wall thermal insulation system with mineral binder and expanded polystyrene granule aggregate (mineral binder composited system) and the decorative insulated exterior wall panel system (decorative panel system). The materials of thermal insulation layer of the exterior wall insulation systmes include commonly used rigid polyurethane foam(RPUF), expanded polystyrene foam(EPS) and extruded polystyrene foam(XPS).Firstly, the thermogravimetric studies were conducted on the commercial grade RPUF, EPS and XPS. The dependence of the activation energy on the conversion degree was evaluated by using the isoconversional methods. The multivariate non-linear regression method was applied for investigation the kinetic model and the corresponding kinetic parameters. Based on the kinetics parameters and the kinetic models, the lifetime of EPS at different temperature was predicted.Secondly, based on cone calorimeter experiments of small scale samples of exterior wall insulation systems, the effects of protective layers on preventing the heat penetration and reducing the heat release rate were evaluated. The performances of the protective layer to prevent heat penetration is mainly reflected in two aspects: First, inhibits the temperature of each layers within the system which also reduces the peak temperature; Second, suppresses the heating rate which delays the time of material to pyrolysis and to reach peak temperature. For the first aspect, two parameters were used for evaluation, that is, the temperature differences between the two sides of protective layer and the internal temperature differences of corresponding locations between samples with and without protective layer. The second aspect was quantified and compared by the time when the system reached the threshold temperature. The protective layer reduces the rate of organic insulation materials to generate the combustible gas which eventually resulted in the reduction of heat release rate. The extent of reduction was evaluated by the peak heat release rate, the average effective heat of combustion and the time to peak heat release rate.In order to further investigate the special fire behavior of the exterior wall insulation systems, such as the flame spread in cavities and the melt, dripping burning of polystyrene foam, the large scale experiments were conducted on the thin-plastering system based on the ISO9705test rig. By measuring the time to ignition, the heat release rate and the internal temperature, the fire prevention effectiveness of the protective layers was evaluated and the influences of the cavity and the dripping burning on the experimental results were analyzed.It is considered that the fire growth rate and the fire intensity are the key factors for the fire spread risk assessment of the exterior wall insulation systems. The fire growth rate was characterized by the ratio of the peak heat release rate(PHRR) and the ignition time and the fire intensity was described by the average effective heat of combustion. The PHRR/ignition time was set as the abscissa axis and the average effective heat of combustion was set as the vertical axis with the aim to draw the two-dimensional fire spread risk maps and to compare the relative risk of fire spread among different types of exterior wall insulation systems.