Abstract:

【Objective】The combustibility of forest combustibles is mainly affected by surface combustibles and litter; hence, it is a comprehensive manifestation of different types of combustibles. Leaves, as small combustibles, affect the initial combustion and have an impact on fire behaviors during the period of fire spread. With the aim of obtaining combustion performances, and providing a scientific and theoretical basis for the forest fire behavior prediction, leaves from four trees, namely Erythrophleum fordii, Pinus massoniana, Acacia confusa and Castanopsis hystrix, were collected in Guangxi in December 2018 as research objects and measured those flammability. 【Method】 In this study, a cone calorimeter was used to test the combustion performance. It can be used to evaluate the combustion performance of materials, the flame-retardant mechanism of materials, and aid in the fire model building, which are the more advanced methods for small-scale combustion tests in the laboratory at present. The radiant heat flow was set to 50 kW/m ². During the experiment, it was necessary to observe and record the phenomena occurring in the experiment, including smoke, deformation, shrinkage, ignition and extinguishment. Furthermore, during the experiment, the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke release (TSR), mass loss rate (MLR) and other parameters were obtained. 【Result】 ① The HRR and MLR curves of Erythrophleum fordii and Castanopsis hystrix, respectively, were similar; while the HRR and MLR curves of Pinus massoniana and Acacia confusa, respectively, were similar. The THR, SPR and TSR curves of the four combustibles exhibited the same changing trends but with different values. ② The maximum HRR value was 285.22 kW/m ², which was obtained from Acacia confusa. The HRR value of Pinus massoniana was 229.85 kW/m ², which is higher than that of Castanopsis hystrix, which had a value of 216.10 kW/m ². Meanwhile, the HRR value of Erythrophleum fordii was the lowest, which was 200.12 kW/m ². The greater the release rate (HRR), the faster the thermal cracking speed of the combustible surface, which accelerates the flame expansion and spread, and increases its fire risk. The THR values of four types of combustibles were as follows: Erythrophleum fordii > Castanopsis hystrix > Acacia confusa > Pinus massoniana. Acacia confusa was the first to reach the highest value. Generally, the leaves that reach the highest value first are easier to burn. The SPR value of Erythrophleum fordii was 0.07 m ²/s, which is higher than that of Acacia confusa, which was 0.05 m ²/s. Additionally, the SPR of Pinus massoniana was 0.04 m ²/s, which was the same as that of Castanopsis hystrix. The TSR of Erythrophleum fordii was 191.94 m ²/m², which was the highest when compared to the other three types of combustibles. Meanwhile, the TSR of Castanopsis hystrix was 162.83 m ²/m², which is higher than Acacia confusa with 119.67 m ²/m². The TSR of Pinus massoniana was the lowest with a value of 95.49 m ²/m². The greater the total smoke release, the greater the risk of fire. The MLR value of Erythrophleum fordii was 4.92 g/s, which is higher than that of Pinus massoniana with a value of 2.68 g/s and the MLR value of Acacia confusa was 2.63 g/s, which was higher than that of Castanopsis hystrix with a value of 1.92 g/s. The MLR curve changes among the four combustibles are basically the same, and all first appeared to exhibit a sharp decline. The time taken for Pinus massoniana and Erythrophleum fordii to reach the maximum mass loss rate was 5 s, and the time taken for Acacia confusa to reach a maximum mass loss rate was 7 s. 【Conclusion】 The combustion performances of different tree species were different. Fire behaviors during forest burning events are very complicated and are made more complex by the diversity of the combustibles. The research results discussed in this paper are only experimental results from small-scale samples and low-intensity radiation levels, which are different from the conditions of the actual combustion process in forest fires. However, through a comparison of the differences in combustibility, we could have a deeper understanding of the combustible properties of combustibles, better explain the differences among the fire behaviors of different combustibles, and provide a scientific method for the development of biological fire protection.

Key words: arbor species, cone calorimeter, flammability, heat release rate, total heat release, Guangxi