This gas is hydrogen sulfide, rises up and mixes with oxygen in the underground water that sits in the cracks and fissures in the limestone.

这种气体是硫化氢，上升后与石灰岩裂缝中地下水的氧气混合。

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Sulfur gas appears reddish, hydrogen is green and oxygen is blue.

硫磺气体呈红色；氢气呈绿色；氧气呈蓝色。

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Since hydrogen gas is extremely combustible, when enough hydrogen gas is mixed with air, it reacts with oxygen. If there is enough hydrogen gas, it will react rapidly, producing an explosion.

因为氢气是高可燃气体，当足够多的氢气进入空气中，它就会跟其中的氧气反应。

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Equally important, the hydrogen-impregnation technique requires far less gas than the oxygen-based one.

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