Emerging risk of autoignition and fire in underground coal storage

The risk and prevention of autoignition in underground coal storage facilities are reviewed in the light of the recent incidents of smouldering fires. Also, the opportunities are considered on the efficiency of the alternatives to prevent and extinguish closed-space fires. The complexities in avoiding and extinguishing underground fires are highlighted in the case example, describing the observations and outcome of a smouldering coal fire in the storage. The principles of self-heating and most critical factors in spontaneous combustion such as the condition and quality of coal are fairly well known, but usually only provide partial help in fire prevention. The documented cases and the case example suggest that nitrogen injection can be useful for extinguishing controllable fires. Three-phase foams and oxygen-displacing exhaust gases appear preferable against uncontrolled fires, particularly if access to the fire area is limited or impossible. Otherwise, efficient fire extinction during power plant operation can be challenging, as any air ingress tends to feed the fire and results in losses of the extinguishing agent and the heating value of coal. Methods and indicators for detecting and predicting the ignition are discussed, and improvements are suggested to enhance the storage and plant availability.