Page 106 of The Secret of Secrets (Robert Langdon #6)

Everett Finch burst through the compromised entrance of Crucifix Bastion and stormed down the hall into the glass-walled atrium.

Where the hell is everyone?! Enraged to find no trace of Housemore or the embassy’s promised security detail, he pulled out his personal RFID key card and headed for the elevator.

As he crossed the room, the key card’s biometric sensors activated in his fingertips, but he stopped short, reminded that there was no possible way for Housemore—or anyone for that matter—to access the elevator down to Threshold.

She must be upstairs…or else she left the bastion for some reason?

He dialed Housemore’s line one last time.

As soon as Finch placed the call, a phone began chirping nearby. Odd. The sound seemed to be emanating from a couch against the far wall. Did Housemore lose her phone? At least it would explain why she hadn’t answered earlier.

Finch strode to the couch but saw no phone. The ringing had stopped, and he called again. Once more, a phone began to chirp. Is it beneath the couch?

Finch crouched down to look under the stylish furniture.

As he stared into the dark space, he knew instantly that Threshold was under attack.

Staring back at him were two dead eyes—the lifeless gaze of his field officer Susan Housemore.

In the frigid vault, The Golěm gazed at the powerful machine sitting before him.

The device’s gleaming metal body was a bulbous ring of polished aluminum that occupied nearly the entire concrete chamber.

Five meters across and one meter tall, the machine resembled a giant metal donut.

The unusual donut shape—technically “toroidal,” according to The Golěm’s research this morning—was apparently the most efficient shape in which to wrap superconducting coils if one wanted to create a magnetic field capable of storing vast amounts of energy.

SMES, he thought. Superconducting magnetic energy storage.

This was the secret source of Threshold’s power.

The Golěm had learned this morning that energy fed into the toroidal magnetic field would race in loops indefinitely with no degradation and could be siphoned off as needed. The only prerequisite was to keep the superconducting coils cold.

Extremely cold.

The critical temperature for its coils was somewhere below negative-260 Celsius, and if the coils rose even slightly above this temperature, they lost superconductivity and began resisting the current.

That resistance caused rapid heating of the coils, which in turn caused more resistance, and within seconds the feedback loop blossomed out of control…

resulting in a dangerous event known as a quench.

To prevent quenching, the coils were continuously flushed in a bath of the coldest liquid on earth. Liquid helium.

He gazed past the SMES to the adjoining chamber, where, locked within a Mu-metal mesh cage, stood twelve austenitic, stainless-steel tanks of liquid helium.

Each of the five-hundred-gallon, Cryofab flasks stood as tall as The Golěm and was equipped with a cryogenic bayonet and vacuum-jacketed piping that transported the cold liquid into the SMES to keep the superconductors cold.

Liquid helium, by most measurements, was harmless—nonexplosive, nonflammable, and nonpoisonous.

Its sole dangerous quality was possessing the lowest boiling point of any substance known to man…

a frigid negative -270 Celsius. This meant that if the helium was permitted to “warm up” above negative-270 Celsius—already near absolute zero—it immediately boiled and converted to helium gas.

The gas itself was also harmless, but the danger lay in the physics of the conversion process. Liquid helium’s conversion to gas was shockingly fast and violent…and, as it turned out, it was the entire reason Threshold had co-opted the R2-D2 vent in Folimanka Park.

When liquid helium converted to gas, its volume multiplied by a mind-boggling ratio of 1 to 750. This meant that the liquid helium in this vault, if released, would rapidly convert to enough gas to fill seven Olympic swimming pools.

In an unvented space, the new volume would have nowhere to go, and the pressure buildup would happen so fast that it would create a “pressure bomb”—a near-instantaneous, violent outward force expanding in all directions.

In a desperate attempt to make room for itself, the gas would blow apart whatever constrained it, resulting in a shock wave much like that of a tactical nuclear weapon, tearing through everything in a given radius.

To mitigate risk, all facilities using liquid helium, including hospitals with MRI machines, were required to install a “quench vent”—a ventilation pipe that ascended up through the roof of the building—to ensure that, in the event of an inadvertent helium leak, the rapidly expanding gas would have a safe alternate route to escape…

rather than blowing up the building. Threshold’s quench vent was massive, but then again, so was the quantity of liquid helium stored down here.

The Golěm gazed again past the SMES to the twelve Cryofab flasks. More than twenty thousand liters of helium, he had calculated. The expansion potential was almost incalculable.

Catastrophic explosions with liquid helium, he had learned online, were fairly common—including SpaceX’s Falcon 9 rocket, CERN’s Large Hadron Collider, and even a veterinary clinic in New Jersey whose MRI had a small leak and exploded.

The Golěm knew that if this SMES quenched unexpectedly, the liquid helium loaded into the system would instantly boil off in a torrent of expanding gas racing up the conduit and shooting skyward over Prague in a geyser of freezing-cold helium.

Most likely blasting off R2-D2’s head in the process.

The liquid helium loaded into the SMES machine at any time represented a very small portion of the total volume contained in the tanks. The Golěm could not begin to imagine what would happen if all the helium in this facility were released at once…converting from liquid to gas in an instant.

Such an event had never occurred. Ever. Anywhere.

There were too many fail-safes.

Helium flasks were extremely robust with multiple safety features.

Built like giant Thermoses, their double-hulled “Dewar” design employed nature’s most efficient insulator—a pure vacuum—to ensure the liquid inside stayed cold enough never to convert to gas.

For additional safety, each flask stored its liquid under extremely high pressure.

This raised the helium’s boiling point, offering a wider margin of error before it hit critical temperature.

The flask’s final safety measure was a “rupture disk”—a tiny copper disk built into the shell of the tank. An intentional weak spot, the disk was calibrated to rupture if the internal pressure climbed too high…thus averting a cataclysmic tank explosion.

Although rupture disks were designed to explode outward, they would also rupture inward if the pressure outside a canister became too great. Of course, that never happened because nobody was ever careless enough to store liquid helium in an airtight space.

Considering these three fail-safes, the probability of multiple tank failures at the same moment carried a statistical probability of zero.

It simply could not happen.

Not without help.

Reflecting on the horrors inflicted on Sasha by Threshold, The Golěm took a final look at the quietly humming SMES device, savoring the irony. This machine was the secret source of Threshold’s power…and was about to become the agent of its destruction.