American mining production increased earlier this decade as industry sought to reduce its reliance on other countries for key minerals, such as coal for energy and rare-earth metals for use in consumer electronics. But mining is dangerous—working underground carries risks of explosions, fires, flooding, and dangerous concentrations of poisonous gases.

Mine accidents have killed tens of thousands of mine workers worldwide in just the past decade. Most of these accidents occurred in structurally diverse underground mines with extensive labyrinths of interconnected tunnels. As mining progresses, workers move machinery around, which creates a continually changing environment. This makes search and rescue efforts even more complicated than they might otherwise be.

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