This morning I was looking up old-timey bank vaults. You know, the ones that appear in movies just in time to be cracked by a dude with a stethoscope and weird hair. I found the following post on Quora, which was so absolutely fascinating that I'm pasting it here so that it's preserved for posterity in case someone ever needs it when writing a heist book. Without further ado, modern vault construction, according to Quora user Robert Cohen, Senior Director of Private Bullion Sales and Chief Contracts and Legal Specialist for Summit Global Investments Group:
The modern bank vault is a masterpiece of protective engineering. Here's what you need to know -
1) The outer vault "skin" is constructed of conventional mild steel; this is designed to counter the threat of blunt force and prying. And vault hinges are made with sloping bottoms, so there are no visible jacking points. You can forget about breaching attacks by demolition hammers, pry bars, angle grinders and the like.
2) Heavy duty cobalt plates are strategically located behind the vault's locking mechanism; these cobalt plates are designed to thwart drilling attacks. Conventional drill bits will spin against the cobalt shield without ever penetrating it. Admittedly, a "high-tech" safecracker armed with a titanium or diamond drill bit could eventually penetrate the cobalt, but it would likely cost the hapless felon several drills (as the drill bits will outlast the motor) - not to mention a whole lot of time.
3) To resist oxy-acetylene torching, safe manufacturer sandwich a layer of copper alloy into the vault doors. When super-heated, the copper alloy melts and flows; but as soon as the heat is removed, the copper re-solidifies, sealing the hole back up. In addition, an added layer of high-thermal-conductivity cast aluminum operates to dissipate the heat of the torch, further slowing down the cutting process; while some safe-makers incorporate a fire-retardant material that releases noxious smoke when heated, rendering working conditions for the safecracker intolerable.
4) Incorporated into the vault doors and walls is an ingenious patchwork of "re-lockers". Re-lockers are mechanical systems that automatically lock-out the vault when a break-in is detected, rendering further efforts at cracking the vault all but futile. The most common re-lockers detect punching attacks in which the door and the locking mechanism are subjected to external force from, say, hydraulically powered pile-drivers and the like. Thermal link re-lockers, on the other hand, trigger an instant re-lock under high temperatures like those induced by oxy-acetylene cutting torches; while specially tempered, glass-plated re-lockers trigger an automatic re-locking when breached by a pneumatically driven jackhammer or other pneumatic tools.
5) Finally, to counter the threat of tunneling, bank vaults incorporate below-ground "patrol passages" equipped with hidden surveillance video cameras and sophisticated vibration and sound detectors.
Wow, the more you know, right? My favorite part is the copper that re-solidifies to moot the effect of torches. Separately, here's the movie someone needs to make: the Antwerp Diamond Heist.