Air crossing

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A bridge where a return airway passes over (overcast) or under (undercast) an intake airway. It is generally constructed with concrete blocks, structural steel, and/or sheet metal, and is made airtight to prevent intermixing of the two air currents. The mining law requires an air crossing to be so constructed as not to be liable to be damaged in the event of an explosion. Syn: air bridge; bridge; overcrossing; overgate. See also: overcast; undercast. Nelson
Source: Dictionary of Mining, Mineral, and Related Terms

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