PURPOSE: To efficiently carry out cleaning and maintenance work by catching the dust which is discharged, together with the pumped up water which is sprayed on the upper surface of a trough by the fire information signal supplied from a sensor or a periodic cleaning work instruction.

CONSTITUTION: When a living cigarette is dropped on a trough 20, and the dust A on the trough 20 catches fire, and the occurrence of danger of fire is estimated, a smoke or temperature sensor 24 operates to transmit a fire information signal, and a water spraying device 20 operates automatically, and sprays water on the upper surface of the trough 20 from the upper edge position in the aslant direction of the trough 20. The fire on the dust A such as living cigarette is extinguished, and the dust A is discharged aslantly downward in the trough 20 by the water pressure. Further, the dust A which is discharged aslantly downward in the trough 20 is pumped up, together with water, by a drainage device 22 and collected. Accordingly, the cleaning and maintenance work can be carried out efficiently.