Coal mines are a hidden market for concrete block, used to build ventilation walls. Concrete block walls direct the flow of air, gases and dust. A typical underground coal mine may use more than 100,000 concrete blocks for these walls, called "ventilation stoppings" or "brattish walls." Block is also the preferred material for mine seals, which close off abandoned areas. The natural fire resistance of concrete masonry makes it ideal for use in mines, where fire poses an even greater hazard than it does above ground. The high strength and durability of block appeal to mining engineers, who must consider roof cave-ins and explosions in their calculations.
The mine workers have to get as much air to the working face as possible and remove methane and coal dust from the area. To do this, mine workers build ventilation stoppings. By preventing unwanted flow in these passages, the walls direct the flow of intake air to the working face and return air, gases, and dust to the outside.
After they've finished mining a section of the mine, workers have to seal that section off with concrete block. The Mine Safety and Health Administration (MSHA) requires that each seal be:
Constructed of solid concrete blocks of at least 6x8x16 inches, laid with mortar between the joints.
- Hitched (recessed) into the solid sides of the opening to a depth of at least 4 inches and hitched at least 4 inches into the floor.
- At least 16 inches thick.
Concrete masonry remains the material of choice in ventilation stoppings and seals, as well as a popular material for roof supports.