PURPOSE: In the fumigation of two or more closed systems separated each other, the residual gas in the first closed system after fumigation is reused for the fumigation of the next system, and the gas remaining in the first system in a low concentration is dehumidified and adsorbed with activated charcoal.

CONSTITUTION: In the fumigation of two or more closed systems separated each other, the residual fumigation gas (e.g. methyl bromide) in the first closed system is transferred to the next closed system to be fumigated by natural convection or forced circulation. When the concentration of the gas in the first system is lowered to a definite level, the connection between both systems is broken, and the gas remaining in the first system is adsorbed with activated charcoal. When the concentration of the gas is lowered below the permissible limit to man, the gas is discharged to the outer atmosphere.

EFFECT: Since the concentration of the gas to be treated is lowered, the cost for detoxication can be reduced.