The arrangement for introducing a desired quantity of decontamination agent into a containment facility comprises a tank as a storage vessel for storing the decontamination agent in liquid form. A metering apparatus having a spray nozzle is directed into the containment facility so as to atomize the decontamination agent. At least one feed line from the ambient air, a compressed air connection and a control unit are provided to operate the metering apparatus. The metering apparatus has a metering container that comprises a storage chamber that has a defined volume for receiving an individual portion of decontamination agent. The storage chamber is provided so as to successively receive a number (n) of portions of decontamination agent from the tank, and the portion respectively held in the storage chamber is introduced by means of the spray nozzle into the containment facility prior to receiving a subsequent portion.