The degree of ageing, the combustion kinetic performance and the change law of the combustion characteristics of ancient pine were experimentally investigated using thermogravimetric analysis, calorimetry experiments, component analysis experiments and gas chromatography-mass spectrometry analysis. The results show that the hemicellulose, cellulose, lignin and resin contents of the ancient pine decreased by 4.78%, 3.87%, 1.39% and 0.63%, respectively. The volatile content of the ancient pine decreased by 7.37%, while the ash content increased by 5.02%. The terpenes in the ancient pine were almost decomposed, and the calorific value of the ancient pine decreased by 21.54%. The ignition point of ancient pine was 19.83°C lower than that of the fresh pine. The activation energy and heat of the pre-charring stage of the combustion of the ancient pine were 1.37 times and 0.51 times those of the fresh pine, respectively. In contrast, the activation energy and heat of the charring stage of the combustion of the ancient pine were 0.66 times and 1.2 times those of the fresh pine, respectively. The ignition time and peak time of the ancient pine were shorter, and the heat release rate, smoke production rate, specific extinction area and CO production rate were higher than those of fresh pine.

The re-burning of coal seams still occurs in coal fire areas after firefighting projects. A large amount of spontaneous combustion gas products is released from the surface fissure, which can cause air pollution and even threaten the production of surrounding mining areas. However, the distribution characteristics of fissure channels in the re-burning coal fire areas are local and scattered. Therefore, we developed a system for the in situ monitoring of spontaneous combustion gas emissions from fissure channels to conduct field investigations on the re-burning behavior of coal seams to explore the degree of re-burning in the coal fire area. The results showed that re-burning of the coal fire area induced fissure channels with different shapes. The CO₂ concentrations are always higher than the CO concentrations among the spontaneous combustion gas products discharged from the fissure channels. The degree of re-burning of coal seams at different study locations was comprehensively determined using simplified MCE and CO₂/CO ratios. The comprehensive factor α was obtained using the generalized principal component analysis (GPCA) by taking into account spontaneous combustion gas, meteorological factors, and the thermal physical characteristics of fissures. A carbon emission model for local fissure channels in the coal fire area was established, and the daily average carbon emissions at the study location were 2.56 t. Therefore, this provides essential theoretical support for taking corresponding fire extinguishing measures according to the degree of re-burning of the coal fire area.

Polyurethane materials are often used in mines to fill the geological structural areas for pretreatment and plugging. These areas are primarily high-incidence areas of coal spontaneous combustion (CSC). Polyurethane will promote the spontaneous combustion of the remaining coal because of its superior thermal insulation performance. Previous studies have focused on the effect of polyurethane on the spontaneous combustion of coal in air atmosphere, without considering the variation of oxygen concentration in the mining area. The paper investigates the effect of polyurethane on the spontaneous combustion of coal in the mining area under different oxygen concentration conditions according to the variation law of oxygen concentration in the mining area. Herein, thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) coupled methods were used to study the kinetics and gas release laws of a polyurethane–coal mixture. The critical temperature of coal increases with the decrease of oxygen concentration. When the oxygen concentration exceeds 10%, the shift of the thermogravimetric curve to the right is smaller, indicating that the oxygen concentration has less influence on the combustion of a polyurethane–coal mixture. When the oxygen concentration is less than 10%, the shift of the thermogravimetric curve toward a higher temperature is more prominent, indicating that the oxygen concentration has a greater influence on the thermogravimetric curve. Simultaneously, the maximum value of DTG increases with the increasing oxygen concentration. The main gas products of coal pyrolysis are CO₂, CH₄, and H₂O, while those of polyurethane pyrolysis are mainly CO₂, CO, CH₄, and H₂O during the pyrolysis process. The amount of CO₂ during the pyrolysis of various proportions of coal and polyurethane is the main difference in the gas products. Coal can promote the pyrolysis of polyurethane to some extent. The characteristic temperature rises and falls as the proportion of polyurethane in the polyurethane–coal mixture changes. In the actual monitoring, small amounts of H₂O, CO₂, and CO gases appear in the starting phase, then a large increase in the amount of gases can be considered that polyurethane is involved in the relevant combustion reactions, which can avoid misjudgment of the spontaneous combustion of coal in the mining area.

Air-doors are important facilities for regulating the air flow in a mine ventilation network. It is of value to study the influence of air-doors, which are adjacent to a fire source on smoke back-layering in order to build a rational ventilation system. By regulating air-doors in a mine ventilation network test platform, two typical mine ventilation networks, with parallel branches and a diagonal branch, were constructed. During the study, into the closing degree of the air-doors adjacent to a fire source in a ventilation network with parallel branches, the back-layering length is up to 3.70 m when the ventilation velocity is 1.40 m/s. When the air-door on the return side of the adjacent branch is closed, the back-layering subsides within 1 min and the upstream temperature drops rapidly to normal. When the air-door is half closed, there is still a back-layering flow within 5 min. Smoke control, with the air-door is closed, is better than when the air-door is half closed. Based on this, tests into the influence of the closing position of air-doors, which are adjacent to a fire source, were carried out in a ventilation network with a diagonal branch. Results indicate that when the ventilation velocity is 1.70 m/s, the back-layering flow spreads to the diagonal branch, and the air flow velocity of both the adjacent branch and the diagonal branch increases. When closing the air-door on the return side of the adjacent branch, the back-layering rapidly subsided. The wind velocity on the intake side of the adjacent branch is stabilized after a rapid decrease, and the wind velocity of the diagonal branch is stabilized after a rapid increase. When closing the air-door on the intake side of the adjacent branch, the smoke from the diagonal branch spreads. Compared with closing the intake side air-door, closing the air-door on the return side of the adjacent branch is more effective in preventing back-layering. This work provides a reference for preventing back-layering and guiding the evacuation of people from the upstream of a fire source.