Deep below the surface, in massive underground caverns packed in salt, lie Germany’s emergency reserves of oil and natural gas. Cavern storage facilities play a central role in the country’s energy policy. Around one quarter of the energy that Germany consumes in a year is stored underground, in addition to millions of tons of oil - part of the national security plan for times of crisis. Until now, the technology used to store the reserves has been considered safe. But hundred-meter long stretches of subterranean pipeline represent a potential risk, similar to fracking. And there are increasing signs that regulators’ technical monitoring of Germany’s underground oil and gas reserves is not up to scratch.