As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN₂) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the cooling and inerting effects of LN₂ injected into a confined space. A confined-space experimental platform was developed to study the injecting LN₂ into the platform with different injection parameters, such as mass flux, pipe diameter, and inclination angle. In addition, a mathematical model of quantitatively assessing cooling and inerting effects was proposed by using heat transfer capacity, inerting coefficient, and cooling rate. Results showed that the inerting effect was gradually enhanced with a mass flux increasing from 0.014 to 0.026 kg/s and then tended to level off; an appropriate pipe diameter of 12 mm was optimal for the cooling and inerting effects in this experiment. In addition, a positively increasing inclination angle could contribute to the cooling and inerting effects. However, there was little effect on the cooling and inerting with an inclination angle less than 0°. This study can provide technical guidances for environmentally friendly fire extinguishing with LN₂ in a confined space.

Coking coal was extracted with tetrahydrofuran solvent using ultrasonic and microwave-assisted method at 50°C and atmospheric pressure. Wettability of raw coal and its residue (residual coal) was tested with capillary penetration method. The raw and residual coals were studied by Fourier transform infrared spectroscopy (FTIR) with curve-fitting analysis. The variation of main surface functional groups of coking coal before and after extraction and its effect on wettability were analyzed. The results were obtained as the following: after extraction with tetrahydrofuran, hydroxyl, ether oxygen, and carbonyl in the coal structure were dissolved, the content of hydrophilic functional groups reduced, and then the hydrophobicity of coal enhanced. At the same time, part of aliphatic hydrocarbon dissolved, the length of aliphatic chains (I2) decreased from 3.961 of raw coal to 3.636 of residual coal, the length of aliphatic chains became shorter, aliphatic CH₂ side-chains decreased and aliphatic CH₃ side-chains increased, and hydrophobic functional groups content increased. In the aromatic structure, four hydrogens per ring increased and two, three, and five hydrogens per ring decreased. Reduction of substitution functional groups and aliphatic hydrocarbon decreased with the side-chains breakage produce more active sites, which increases the degree of condensation of the aromatic ring (I3). The combined action of the decrease of the hydrophilic functional groups and the increase of the hydrophobic functional groups made the wettability of the coking coal become weak.

This study aims at achieving the generation laws of the iconic gas compositions produced during the process of the cotton smoldering. A mini tube furnace was used to heat a long-staple cotton sample from Xinjiang, China, and a gas chromatography-mass spectrometer (GC/MS) was applied to analyze the produced organic and inorganic gas composition at different low temperatures ranging from 95 °C to 185 °C. Besides, a thermogravimetric experiment under air atmosphere was done in order to verify the correctness of the inferences. The pathways of product generation by heating cotton were set forth, including the depolymerization of the cotton cellulose, the sequential generation of coke, low molecular weight products, long chain carboxylic acids, levoglucosenone, and acetone at 125 °C, and the generation of hydrogen at 95 °C, carbon dioxide, carbon monoxide at 145 °C, and methane during the heating process. The results showed that the alkanes, furans, alkenes, aldehydes, hydrazines, and acids could not be regarded as the iconic gas compositions because of their little proportion, the joint detection of the methane and hydrogen could be used to predicate the smoldering, and the acetone and carbon monoxide could be used to confirm the smoldering stage. The results of the thermogravimetric experiment are consistent with theoretical analysis, indicating that analyses are reliable. This work will provide significant practice foundation for the early warning and prevention of cotton fires.