LF designs and builds geodesic domes for coal storage, petcoke and other combustible bulk materials. Coal is often transported long distances and stocked at various points between the mine and the user. Thus, coal piles come in many shapes, from the huge multiline longitudinal piles frequently found at ports, to ring blending beds at large power plants, to simple conical or irregular piles common at industrial plants.
Although many of the same issues that apply to most other bulk materials are encountered when storing coal, combustibility makes it a special case and deserves careful treatment. The following comments apply also to other combustible materials such as woodchips, grains and sulfur.
The National Fire Protection Association, in its publications NFPA 850 and 120, identifies the hazards associated with storage and handling of coal, and gives recommendations for protection against these hazards. NFPA recommends that coal storage structures be made of non-combustible materials, and that they are designed to minimize the surface area on which dust can settle, including the desirable installation of the cladding underneath a building's structural elements.
The recommendation requires an explanation. First, coal is susceptible to spontaneous combustion due to heating during natural oxidation of new coal surfaces. Second, coal dust is highly combustible and an explosion hazard. If a coal dust cloud is generated inside an enclosed space, and an ignition source is present, an explosion can ensue. Dust clouds may generate wherever loose coal dust accumulates, such as on structural ledges, if there is a nearby impact or vibration due to wind, earthquake, or even maintenance operations.
The table above indicates that explosions occur with concurrence of several factors. But because of coal's propensity to heat spontaneously, ignition sources are almost impossible to eliminate in coal storage and handling, and any enclosed area where loose dust accumulates is at great risk. Further, even a small conflagration can result in a catastrophic "secondary" explosion if the small event releases a much larger dust cloud.