Cologne, Germany: A tank-in-tank system, whereas the inner tank is containing water hazardous fluids and the second wall serves a containment, if the inner wall is experiencing a leakage. The loss will be enclosed in the space between the two tank walls.
<a href="//commons.wikimedia.org/wiki/User:Cccefalon" title="User:Cccefalon">CEphoto, Uwe Aranas</a>
<span class="int-own-work" lang="en">Own work</span>