Experimental study and advanced CFD simulation of fire safety performance of building external wall insulation system

Large scale fire tests of building external wall insulation system were conducted. In the experiment, thermal-couples were mounted to measure the insulation system surface temperature and the gas temperature inside rooms at the second and third floors. Photos were also taken during the fire tests. The measurement provides information of the ignition and fire spread of the external insulation system which consists of surface protection layer, glass fibre net, bonding thin layer, anchor and the load bearing wall. Comprehensive simulations of the fire tests were carried out using an advanced CFD fire simulation software Simtec (Simulation of Thermal Engineering Complex) (1, 2), which is now released by Simtec Soft Sweden, with the turbulent flow, turbulent combustion, thermal radiation, soot formation, convective heat transfer, the fully coupled three dimensional heat transfer inside solid materials, the 'burn-out' of the surface protection layer and the pyrolysis of the insulation layer, etc, all computed. The simulation is compared with experimental measurement for validation. The simulation well captured the burning and fire spread of the external insulation wall. With strategic implementation of building energy conservation, external wall insulation system has been widely used in China. Thin plaster external thermal insulation systems (TPETIS), with advantages such as light weight, low thermal conductivity, wall structure protective, simplicity in construction and etc., have become the most widely used type of wall insulation system. Typical insulating materials used in TPETIS are EPS (Expanded Polystyrene), XPS, (Extruded Polystyrene) PUR (Polyurethane) and PIR (Polyisocyanurate). In recent years, however, a number of serious fire accidents of high-rise building are related to TPETIS. This has drawn people's high attention to the fire safety of TPETIS. The fire performance of TPETIS is mainly affected by factors such as ignition source, system structure and combustion property of the insulation materials. For ignition source factor, Lee (3-5) has analyzed of the spreading mechanism of window fires (the external wall insulation system fire is usually started by window fires) and proposed a new length scale for correlating window fire's flame height, plume temperature and heat flux. Himoto (6) considered pressure gradient effect of window fire plume, and proposed a model for predicting the trajectory of window flame ejected from a fire compartment. For system structure factor, Oleszkiewicz (7) pointed out that laterally projecting structure of building facade can reduce radiant heat flow by 90%, and the vertical extending structure can increase radiation heat flux by 50%. For TPETIS, he also proposed fire-barrier belts to be used between every one or two floors. In recent years, a number of scientists (8-10) have carried out a number of window and corner fire experimental studies and indicated that the systems with improved structure (such as additional This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.