What is required to fill or purge a container that will be abandoned underground?

The requirement to fill or purge a container that will be abandoned underground is specifically to ensure that the container is safe and does not pose a risk of leaking or causing environmental contamination. Filling the container with water or sand serves multiple purposes. Water can prevent the buildup of flammable gases inside the container and minimize the risk of it becoming a hazard. Sand, on the other hand, can help to stabilize the container, making it less likely to collapse or leak once buried.

Using water or sand is a common practice when dealing with abandoned tanks, as these materials effectively eliminate the void space inside the container, reducing the likelihood of the tank floating or shifting in the soil due to groundwater movement. This method is particularly favored in environmental safety protocols, as it complies with regulations intended to protect the surrounding environment from potential leaks or spills.

The other options do not fulfill the safety or regulatory requirements in the same effective manner. For instance, air could lead to the compartment becoming a potential source of flammable gas, while foamed plastic does not provide the structural stability or liquid fill needed. Inert gas might be a viable option in certain controlled situations but is less common for abandoned underground tanks due to practical considerations such as accessibility and cost.