Triple Wall [1]

In "Triple Wall" construction - as regards tanks or containment sumps - two interstices are present and both are continuously monitored. In this case, only two of the three walls can truly be breached, the innermost, and the outermost. A breach in one wall or another would be backed up by the integrity of the other.

See also underground storage tank [2], tank [3] and double wall tank [4].