PITTSBURGH (AP) — In the tomb-like chill of a dim mine shaft hundreds of feet underground, workers chip away at ribs of limestone with hand tools and a hydraulic jackhammer.

Where miners in the early 1900s had hauled rock to the surface for use in steelmaking, those working in the mine on a recent workday were preparing to add a layer of wall paint. Then they would install a white tile floor, then a white ceiling with clinically clean lighting — transforming the limestone tunnel into a space with a constant temperature and humidity.

Iron Mountain can show off plenty of these rooms across more than 200 acres of underground space carved into an abandoned limestone mine in Butler County. The facility — famous for its geology and for holding some of the most precious pieces of paper and film in America — lately has been installing large racks of blinking computer servers that stretch as far as the eye can see.

The Boston-based information management company that owns the mine has been advancing deeper into the shafts to serve health care and insurance businesses, financial institutions and tech companies looking for the safest place to store their irreplaceable digital information.

By this spring, Iron Mountain expects another 11 acres of the former mine to be in use by clients storing digital data.

Iron Mountain portrays its mine as optimal for businesses that want the highest level of security at a reasonable price. The security comes in the form of armed guards and metal detectors at the entrance all employees and visitors walk through.

It also comes with the 20-foot-thick seam limestone — bound by layers of impermeable shale rock — that could largely withstand any explosion. (Slight imprints from dynamite blasting can still be seen on the walls.)

And security is found in digital defenses: The facility's computer system is entirely disconnected from the internet, and its computers won't allow anyone to plug in an external hard drive.

The company touts its client base of highly regulated and sensitive companies that have bought into those assurances. In fact, the federal government uses a significant part of the mine, employing most of the 2,000 workers who enter and leave the facility each day.

When Iron Mountain purchased the data center in 1998, much of the storage was used for paper and film — patents, motion pictures, Social Security applications filed by every resident of the United States, pension records, boxes of business records.

Changes to how businesses manage information, including the popularity of cloud storage, have been a boon to Iron Mountain and other companies that manage data centers. Cloud storage is a computing model that allows companies to put data on remote servers accessed from the internet.

Last year, 95 percent of companies were using the cloud in some way, according to a survey published by RightScale, a Santa Barbara, Calif.-based cloud services provider.

"The cloud decision kind of breaks the mindset of the IT department" for companies, said Mark Kidd, senior vice president and general manager of data centers for Iron Mountain.

"As they think, 'Maybe we can send these applications to the cloud,' in that same breath, they think, 'Why are we updating a 30-year-old data center again, with a huge amount of capital? Why don't we just outsource this?'"

Iron Mountain has said about 80 percent of the assets it has received in recent years are digital. A recent tour of the Butler County facility made it obvious where the demand is as Mr. Kidd walked through two empty rooms totaling roughly 21,000 square feet of gleaming white space.

"I know it sounds crazy, but we anticipate by the end of the first quarter this room and that other room will be completely sold," he said.

The mine contains more than 230 private vaults, many of them managed by government agencies like the National Archives and Records Administration, U.S. Patent and Trademark Office and the Social Security Administration.

The mine also houses treasured film records from virtually every major motion picture company in the country, said Troy Hill, senior manager of data center infrastructure for Iron Mountain.

"The product we're offering is space, power, cooling, security," Mr. Hill said.

Operational costs — and therefore the costs of expanding the mine — are much lower than most above-ground facilities. The data center pumps 53-degree water from an underground aquifer to cool its systems.

The mine has two major substations underground that draw power from West Penn Power's grid network. At full capacity, the Iron Mountain data center could span 500,000 square feet of space and could consume roughly 40 megawatts of power, enough power for about 40,000 homes, the company said.

The issue of cybersecurity falls largely on each individual client's systems, Mr. Kidd said.

"To be honest, they don't want anyone else liable for it," he said.

Though the mine has never had any intrusions or major incidents, Mr. Hill said, Iron Mountain is always looking for ways to improve security.
Mr. Hill pointed to a copper/?lead door installed for a large insurance company that was concerned about electromagnetic pulses, which can be sent by terrorists or even the natural environment and could cripple equipment. (In addition to the door, a study conducted later at the mine proved that limestone layers naturally shield such waves.)

Iron Mountain also has been trying to eliminate the likelihood of someone bringing down the data center by infecting the building management system with a computer virus.

Despite a filled multi-level parking lot built into the side of a hill, the mine's entrance is easily missed along a two-lane road about 15 minutes northeast from Slippery Rock. Employees descend a long covered walkway and filter through a security check and metal detectors.

At lunch breaks, employees walk along the sides of the airways or zoom around in heated motorized carts. Like a surreal, underground city, some of the vaults are dressed with wood-paneled porches or they fly flags with an agency's seal. The employee cafeteria, the Rodeway Cafe, is decorated to look like a homey storefront with an inviting red awning.

But those are just the few reminders of the outside world in the subterranean catacombs.

Aside from an occasional street sign — Limestone Road, Kilowatt Avenue — there is a noticeable lack of signage in the disorienting labyrinth of tunnels.

"That's intentional," Mr. Hill said. "If you don't know where you are, then you shouldn't be down here."
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Information from: Pittsburgh Post-Gazette, http://www.post-gazette.com