It can happen that a too high concentration of a volatile product is measured in a container. In that case the gas or vapor has to be taken out before the container can be declared fit for safe entering and discharge. This process can be done in two ways:
Natural ventilation: On a safe location the doors are opened during a certain time. The natural ventilation takes the excess of gases away. This is the technique in case of presence of the less dangerous vapors.
Forced ventilation: In a designed and recognized "defumigation zone" fans are connected by means of hoses to the container, trough a special door. The container is mechanically flushed during a certain time. This process will be applied in case of the presence of more toxic gases. In the case fumigation gases are present the exhausted air will be sent trough a filter system, where the fumigants are separated from the exhaust air.
Of course, after each ventilation operation a quality check must be performed. For this, fans are disconnected and/or container doors closed, for at least two hours. Then a new gas measurement is carried out. In most cases the container can then be released for safe discharge.