This thesis aims to address the root causes and means of prevention, mitigation and other improvements to the challenges from smouldering fires, coal freezing and occupational risk in an underground storage silo built into granite bedrock. In addition, appropriate performance indicators are suggested, and the benefits of the recommended or adopted actions are estimated. The issues and observed incidents demonstrate hazards that are largely classified to represent issues of emerging risk. To reduce the fire risk, successful measures included bottom maintenance door sealing and modified design of silo filling and discharge. The assessed benefits of these actions suggest a payback period of only about 10 days, assuming that, without these measures, a fire like the one in 2008 could occur once in four years. Additional recommendations are made to reduce air flow through the coal bed and near the silo ceiling, and to improve nitrogen purging at the hoppers. Filling with subzero coal can freeze silo drains, resulting in water inflow and further freezing to hamper discharge. As the heat flow is unlike any previously known cases of coal freezing, conventional mitigation e.g. by freeze conditioning agents, would not help. After implementing modified filling procedures for cold coal, no severe freezing cases have occurred. Safety advantages from the automated and remotely controlled operation do not necessarily apply under exceptional circumstances requiring human involvement. As preventive measures, protection has been sought from additional technical barriers and training effort. The rarity of serious incidents is a challenge in demonstrating success, but also emphasizes the importance of using leading (not only lagging) safety performance indicators for measurable safety promotion. In contrast, suitable leading performance indicators of the fire risk have been suggested for deliveries as an index of coal properties and for storage (gas emissions and temperature). Suggested leading indicators of the freezing risk can be based on adverse weather along the transport route, delivery of wet cold coal, and the flow rate of seepage water entering silos with cold coal.New challenges could arise from the increasing use of biomass fuels with high volatile contents that may facilitate relatively easy autoignition, high moisture content to ease freezing, and a low heating value that increases the transported and stored volumes and may thereby elevate the associated risks.
|Translated title of the contribution||Maanalaisen kivihiilivaraston uudet riskitekijät|
|Publication status||Published - 2013|
|MoE publication type||G5 Doctoral dissertation (article)|
- underground storage
- smouldering fire
- performance indicator