Underground "nuke proof" data bunkers have been used in commercial storage for decades. In recent years, subterranean bunkers have emerged as a growing niche in the data center ecosystem. Perhaps no company reflects that transition as well as Iron Mountain, a traditional leader in document storage that is now building a digital storage empire.

The flagship facility in the company's push into the data center sector is a huge underground facility in western Pennsylvania. Iron Mountain bought the former limestone mine, which houses 1.7 million square feet of space, from the National Underground in 1998. It has developed a section of the mine into an energy-efficient data center known as Room 48.

Located more than 200 feet underground, Room 48 takes advantage of its subterranean environment. The mine's temperature remains steady at 55 degrees and the imestone walls to absorb heat eliminate the need for typical data center cooling systems that consume large amounts of power.

The mine was opened in 1902 by U.S. Steel to provide limestone for its operations, but the company abandoned the site in 1952. The founders of National Underground Storage then bought 80 acres for record storage, and soon convinced federal officials to store vital documents in the old mine to preserve them in the event of a nuclear attack. Around the same time, Herman Knaust founded Iron Mountain in a former iron ore mine in Livingston, N.Y. Their paths intersected in 1998, when Iron Mountain acquired the National Underground site for $39 million.

Today more than 2,700 employees work in underground records vaults spread over 130 acres. About 150 of those are Iron Mountain employees, with the remainder working for the company's many customers.The facility has its own restaurant, fire trucks, water treatment plant and backup power infrastructure.

Next: Inside The Data Center

Iron Mountain's Energy Efficient Bunker (Main)

Inside the Data Center | Cooling & Containment | Lighting & Power