According to the safety regulations, how must underground ASME containers be set?

The correct choice indicates that underground ASME (American Society of Mechanical Engineers) containers must be set level to ensure safety and operational integrity. When these containers are placed underground, it is crucial that they are installed horizontally and uniformly to avoid structural stress and potential failure. A level installation helps distribute the weight evenly and reduces the risk of shifting or movement, which could lead to leaks or malfunctions in the gas delivery system.

Furthermore, when containers are not set level, issues such as improper sealing can arise, leading to dangerous situations, including gas leaks. Additionally, a level installation aids in proper drainage of any water that might accumulate, thus preventing corrosion and extending the life of the container.

The other options do not align with safety regulations; leaning towards a wall, setting at an angle, or floating in water do not provide the stability and structural support necessary for safe operation. These practices could compromise the integrity of the container and pose significant risks to public safety.