Flame spread over the surface of thermal insulation materials in different environments

HUANG XinJie 0 SUN JinHua ) 0 JI Jie 0 ZHANG Ying 0 WANG QingSong 0 ZHANG Yi 0 0 State Key Laboratory of Fire Science, University of Science and Technology of China , Hefei 230026, China Experiments were conducted in a plateau area in Lhasa and a plain area in Hefei China to investigate the flame spread characteristics on thermal insulation materials under different environmental conditions (pressure and oxygen concentration). Molded polystyrene foam (EPS) and extruded polystyrene foam (XPS) samples were placed horizontally on a small-scale flame spread experimental bench. Changes in the average length of the pool fire, flame spread speed,average flame height, and length of preheating zone were used to determine the effect of the plateau and plain environments on flame spread characteristics. These parameters were all larger in Hefei than in Lhasa, which indicates the fire hazard in Hefei will be higher than that in Lhasa if insulation materials of the same size are used. - Global energy problems are one of the major constraints on growth of the world economy and sustainable development. The energy consumption of buildings in China is a major problem. Therefore, energy-efficient building methods are a focus of development. External insulation materials provide good insulation and are widely used in high-rise buildings. Currently, both international and Chinese high-rise buildings mainly use organic polymer foam insulation boards for thermal insulation. These materials include molded polystyrene foam (EPS) and extruded polystyrene foam (XPS). Fire safety is a concern with these insulation materials as they rapidly combust and show high heat release, flame temperature, smoke volume, and release of toxins. A fire involving these materials occurred on February 9, 2009, on the north side of the China Central Television (CCTV) building. Fireworks lit the insulation material (XPS) in the external facade. The fire spread rapidly, and eventually ignited the entire building. It resulted in the death of a fireman, injury of seven people, and the direct economic loss of several billion Yuan. This case illustrates the important practical significance of systematic studies on the spread of fire in insulation materials. Flame spread speed in many cases determines the severity of the fire. Flame spread characteristics have been evaluated in a number of different insulation materials. Lie [1] studied flame spread in two typical insulation materials, the thermoplastic EPS and the thermoset plastic polyurethane foam PU, in hollow walls created by two concrete slabs with different-sized air gaps. Oleszkiewicz [2] measured full-size flame spread characteristics, including the distance of flame spread and the maximum heat flux, in exterior insulation materials to evaluate the fire risk of different insulation materials. The changes in flame speed have also been investigated in many typical foams and other combustible materials placed horizontally under external radiation [3]. Liang et al. [4] studied decorative thermoplastic EPS using the large-scale ISO9705 test. They attributed the flame spread of the insulating materials to flow combustion, and the liquidity of molten materials was an important factor in this combustion. However, there are few studies that have The Author(s) 2011. This article is published with open access at Springerlink.com investigated flame spread characteristics of materials under different environmental conditions, such as pressure and oxygen concentration. These studies include an investigation of the flame spread characteristics of white wood carbonized solid fuel at high altitude, and the comparison of flame spread speed, flame height, flame temperature and other parameters in Lhasa and Hefei, China [57]. In consideration of the large size of China, and the resulting large temperature gradients north to south and changes in altitude east to west, studies of flame spread of insulation materials under different conditions are practically important. In this paper, small-scale EPS and XPS flame spread experiments were conducted in a plateau area in Lhasa and a plain area in Hefei. Insulation material of the same size was placed horizontally and ignited, and the average length of the pool fire, flame spread speed, average flame height and length of preheating zone were analyzed. Experimental Experimental system Experiments were carried out using a small-scale flame spread setup (Figure 1) including a rotating support of gypsum board and a measurement system. Insulation materials could be placed at different angles on the gypsum board to perform one-sided flame spread experiments. The measurement system included a thermocouple, radiation heat flow meter, camera and data acquisition system, and a heat flux acquisition device. The gas temperature and internal temperatures of the insulation materials were measured by the thermocouple during the flame spread process. The heat flux meter was used to measure radiation heat flux in the process of flame spread. The camera recorded the flame spread process. The data were used to establish the relationship between insulation material pyrolysis front and flame spread time. 1.2 Sample preparation and experimental Both the insulation materials, EPS and XPS, were of the same size (80 cm length, 4 cm width, 4 cm thickness). The densities were 18 and 36 kg/m3 for EPS and XPS. The bottom surface of each sample was wrapped with aluminum foil to prevent molten insulation materials from flowing onto the gypsum board. A set of parallel lines were drawn at 5-cm intervals on the upper surface of each sample to facilitate instantaneous recording of the position of the pyrolysis front during flame spread. Before the experiment, the sample was placed on the gypsum board and the thermocouple was positioned on the upper surface in the middle to measure the surface temperature during flame spread. Results and discussion The flame spread experiments were carried out in Lhasa and Hefei, which have different geographical and meteorological conditions (Table 1). The Lhasa area is hypobaric and hypoxic, while Hefei has normal pressure and oxygen concentration. Flame spread experiments in these two locations can represent the characteristics of flame spread at different atmospheric pressure and oxygen concentration. Flame spread characteristics The insulation materials EPS and XPS are typical thermoFigure 1 Small-scale experimental system used to study flame spread on insulation materials. (a) Rotary experimental stent system; (b) measurement system of flame spread characteristics. plastic materials, and each has a characteristic combustion process. The flame shapes can reflect the characteristics of flame spread on the insulation material, and those for the EPS sample in Lhasa are shown in Figure 2. EPS, XPS and other thermoplastic solid materials have a different flame spread process to carbonized solid materials. The combustion zone on (...truncated)