Only a few vendors are offering oxygen-deprivation systems, but interest in the technology is growing. It involves pumping air that has such a low oxygen content that a fire can't start in the data center.

Air is composed of about 21% oxygen, 78% nitrogen and 1% other gases. Fire needs the oxygen to burn, and lower percentages of oxygen make it more difficult or impossible for fire to start.

N2telligence GmbH, a start-up company based in Hamburg, Germany, has taken the oxygen-deprivation concept a step further by using a fuel cell. The fuel cell provides two functions: it can supply low-oxygen air to the data center and power during a sudden outage, said Lars Frahm, one of N2telligence's co-founders.

N2telligence showed a fuel cell at CeBIT that uses two, 50-liter tanks of hydrogen for fuel. It's made by Plug Power Inc. in Latham, N.Y. The air that's discharged from the fuel cell reaction has less oxygen, and a condenser removes a bit of water vapor before the air is pumped inside the data center, Frahm said.

The air "is even worth more than the electricity that comes out of it," Frahm said.

But that electricity can also be used in case of a power failure. N2telligence's fuel cell is equipped with a battery to immediately supply power to the data center while the fuel cell reaction starts, usually within a few seconds, Frahm said. Overall, fuel cell technology is best for small data centers, Frahm said.

Both N2telligence and Wagner were reluctant to quote a cost for their systems, as it depends on the air-tightness of a data center and its size, among other factors, they said. Wagner has sold about 200 systems over the last couple years as demand has grown, said Peter Clauss, Wagner sales director.

N2telligence was formed in July 2006 and just put up its Web site last week, Frahm said. The three-person company is self-funded, although a partnership is expected soon with Kidde, the fire safety division of United Technologies Corp., he said.