The invention relates to a dual wall cylindrical container with a gas distribution source in the lower portion thereof. The cylindrical container is positioned at the lower portion of a frame with two suction sources for potentially pollutant gases. The first source has the highest gas charge and extends from the space defined by the dual wall of the cylinder and is connected to an active-carbon dynamic extraction system. The second source extends from the gap between the upper edge of the open cylinder and the frame, and is connected to a global network for discharging and processing the charged air. A third suction source extends from the two horizontal work planes provided with sieves for suction from the top to the bottom. The gas distribution source is provided with a safety device that cuts off the supply of gases when detecting an abnormality in the suction circuits.
