When radon ventilation fans are added radon levels can even be reduced further.

当增加氡换气扇时，可进一步降低氡的水平。

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Even powerful ventilation fans don't effectively remove secondhand smoke from the air.

看似功效强大的通风设备并不能有效清除二手烟。

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What is more, tunnels need power for lights and ventilation fans, and to run pumps when they flood, whereas Bridges require almost none.

除此之外，隧道需要电能来为隧道里的灯光与通风扇供电，还需要在隧道被淹的时候使用水泵，而桥梁则不需要这些。

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Running the trains had been more difficult on the Manhattan side of the river, the official said, because there wasn't sufficient power to operate ventilation fans to clear diesel fumes.

WSJ: Buses Back, But Subways Could Take Days Longer

Even late at night, residents can be kept awake by a nearby restaurant's loud pet goose, supermarket or restaurants' ventilation fans and freezers, temples or businesses setting off firecrackers to seek divine protection at ungodly but auspicious hours.

BBC: Taiwan's noise pollution dilemma

It is pitching a new ventilation system that would fill a mine with sensors, dampers and louvers along with variable speed fans that will send only the right amount of air to the mine tunnels.

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