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While the self-heating and spontaneous combustion of coal is a known challenge at coal mines and storage sites, there are known methods for mitigating this challenge for typical open stockpile storage. However, closing the storage will reduce access for corrective action, and it is then important to manage the storage and its transport system with added attention without unduly adding cost or hindering availability. This paper aims to discuss the risk, prevention and extinguishing of fires in closed coal storage facilities, particularly in light of the experience with the Salmisaari underground rock storage facility in Finland. The observed autoignition events have indicated an array of contributing factors, some of which are unique to underground silo storage facilities. On the other hand, many features of the storage facilities can be compared with other extant closed storage systems. The factors affecting fire risk are described and the associated fault and event trees are outlined for autoignition at underground storage. Drawing upon the experiences with past events of self-heating and spontaneous combustion, recommendations are given on cost-effective preventive, corrective and other mitigating action for minimising fire risk and promoting storage availability.
Observed autoignition events and extinguishing the resulting smouldering fires in an underground storage system of a coal-fired power plant have provided insight into the array of contributing variables, and some experience on quantifying the risk with alternative scenarios of event initiation, progress and potential mitigation. Although the first attempts to quantify the risk suggest high sensitivity to the sequence of action taken after fire alarm, and no similar storage sites really exist, some recommended preventive, corrective and other mitigating activities can be at least partly defined and improved by using the cumulative experience and parallel efforts in other closed or underground storage sites. However, there are also so-called black (or at least grey) swans: unexpected events for which the facility may be poorly prepared for. In the case of the underground storage silos, such an event was experienced when incoming cold coal during a harsh winter season froze the sewer system that normally protects the stored coal from seepage water. With blocked normal bypass, the seepage water found its way to the coal silos and created large clumps of icy coal that blocked the coal conveyors. Although freezing weather is not unusual at high-latitude power plants, the common methods to combat freezing of coal are mainly useful for open storage sites and above-ground transport. Options for mitigation are discussed, as well as the event chain leading to an event that had never previously occurred. The case is discussed from the point of view of options to prepare for rare or unforeseen events.