General ventilation dilutes the concentration of the solvent in the air of a room or space. To properly control solvent fumes, activated carbon filters adsorb chemical fumes removing them from the air. Adsorption works when the chemical reacts with the carbon sticking to the surface effectively removing it from the airflow. Activated carbon filters are treated to increase the surface area to improve adsorption. When small amounts of solvents are used or the solvents are low toxicity, general ventilation is usually adequate. General ventilation may be as simple as opening a door/window or installing a wall or roof fan to bring in fresh air.