PROBLEM TO BE SOLVED: To solve such a problem that the earth's atmosphere becomes a volcanic outside air comprising fine particles and volcanic gas-containing air for a long period of time on a global scale, and an operation of an active equipment is impaired in the volcanic outside air and there is such a risk that a situation having to force stopping may occur, and consequently, the way of ventilation in order to take in clean air of a conventional degree is the problem to be solved without changing a structure in the building containing the active equipment and without changing the active equipment.SOLUTION: A volcanic outside air ventilation device is laid in a building, and a pressure of clean air inside the building is increased higher than the pressure of the volcanic outside air outside the building.
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