The indicative ability of a gas indicator for the spontaneous combustion of coal is affected by the secondary oxidation of oxidized coal, from old goafs, entering a new goaf through air leakages. This phenomenon can affect the accuracy of early warning systems regarding the spontaneous combustion of coal in a goaf. In this research, three kinds of coal were selected to carry out a spontaneous combustion simulation experiment in which a temperature-programmed experimental device was used to analyze the behavior of the index gas towards raw coal and oxidized coal, for which the latter was oxidized at 70 °C, 90 °C, 130 °C, and 150 °C. The results show that the chain alkane ratio in the secondary oxidation process and the trends of oxygen, CO, and C₂H₄ concentrations are the same as those in the primary oxidation process. On the other hand, the temperature at which C₂H₄ initially appears, during secondary oxidation, is lower than in primary oxidation. The CO produced in the early stage of secondary oxidation is greater than the CO produced, at the same temperature, in primary oxidation. In this regard, the usage of C₂H₄ concentration as an indicator with which to judge the occurrence of the spontaneous combustion of coal would allow for an earlier response. In the secondary oxidation process, the temperature of the extreme value of the alkene ratio appears higher than in primary oxidation. The presence of a higher pre-oxidation temperature and a higher proportion of secondary oxidation gas will affect an indicator’s judgement when the primary oxidation enters the severe oxidation stage. The gas produced by secondary oxidation will affect the early warning of the spontaneous combustion of coal in the coal mine goaf, which should be considered in the establishment of an early warning system.

The refuge chamber provides a safe space where people can stay safe when they are trapped by an accident in a coal mine. The refuge chamber includes several systems such as oxygen supply, air purification, cooling, and dehumidifying. The oxygen supply system is the core of the refuge chamber because it is a closed environment. The oxygen supply time is 96 h according to the relevant standards in America and China. If people stay in the refuge chamber for more than 96 h, the oxygen supply may not be enough, and they can be in danger. It is necessary to efficiently use oxygen and extend the oxygen supply time. Based on the experimental platform of the refuge chamber, this paper conducts an in-depth study on the automatic control of the oxygen supply system. The oxygen supply system and the harmful gas removal system can be automatically and efficiently controlled by the programmable logic controller (PLC) according to the personnel number and the oxygen concentration. The experiment has proved that the system is good and reliable.