Ill yake a stab at it Assumming the vault is the newer style with fiberglass tanks all the metal fittings are grounded to the electrical grid of the proerty.
there have been cases were an electrical tranformer on a pole taken out by a truck sent a surge into the ground and followed water pipes etc and caused buildings upto 2 blocks away to catch fire I bieleieve it was in (electical contractor magazine) the fire was caused where the power surge was able to jump from one object to the other. had a similar thing happen at the radio station i take care of where during a lightning storm the surge came down the tower into the ground went along the wire grid thats under AM tansmission towers and where it came close to a natural gas pipe a suffecent arc set off a gas line explosin.