What cleaning method is appropriate when there is spillage on the exterior that makes ISO markings illegible?

When dealing with spillage on the exterior of a container that renders ISO markings illegible, spot cleaning is the appropriate method. This technique targets the specific areas of concern—such as the spillage affecting the markings—without unnecessarily disturbing the entire container surface.

Spot cleaning typically involves using a suitable cleaning agent and a cloth or sponge to gently clean the affected area, thus restoring the visibility of the ISO markings. This method ensures that the container remains in good condition while also complying with regulations regarding the display of necessary identification markings.

The other cleaning methods listed are not suitable for this situation. Deep cleaning, while thorough, may be excessive and can lead to damage or degradation of the container's exterior and other important features. Disposing of the container would be an inappropriate response to a fixable issue, as it is far more resource-efficient and environmentally friendly to restore the markings rather than discard the entire unit. Additionally, painting over the markings is not advisable because it can obscure important information and violate standards concerning the visibility and legibility of ISO certifications.

In summary, spot cleaning effectively addresses the problem without compromising the container's integrity or compliance, making it the best choice in this scenario.