Abstract: The present document describes a method and confinement unit for stopping a chemical reaction involving hot metal dross and a gas in the surrounding environment. The method comprises transferring the hot metal dross in a dross pan and placing the dross pan with the metal dross therein in the gastight chamber. Then, the dross pan is sealed with the hot metal dross therein into a gastight chamber of a fixed interior volume. The chemical reaction occurring inside the gastight chamber depletes a limited amount of gas present inside the gastight chamber, thereby stopping once the gas is completely depleted. The gastight chamber is shaped and sealed to withstand a pressure differential created by the depleting of the gas in the fixed interior volume, until the hot dross is cooled and the chemical reaction has stopped.