Which of the following is necessary for containers holding waste or dangerous substances?

Containers holding waste or dangerous substances must be suitably constructed to ensure they can safely contain their contents without risk of leakage, contamination, or degradation. This construction is critical for maintaining safety standards and ensuring that the risk of spills or other hazardous incidents is minimized. Suitable materials and designs can help prevent reactions with the substances contained within and withstand environmental conditions.

Labeling and proper maintenance are important as well; however, the fundamental requirement lies in the construction of the containers themselves. Without suitable construction, the other measures would not be effective in ensuring safety and compliance with regulations. While storage outdoors may be necessary in some cases, it is not universally applicable nor a fundamental requirement for all waste containers, particularly those that may need to be kept in controlled environments.