More than 10% of arriving shipping containers have levels of harmful substances above the occupational exposure limits. They are naturally emitted from the goods or were deliberately added for fumgation purposes. Many are neurotoxic or carcinogens with very low exposure limits. They are often difficult to reliably identify and quantify without advanced analytical equipment. When a risk container has been identified, or cannot be confirmed safe to enter, pre-ventilation will lower potentially high arrival concentrations.