The U.S. Department of Transportation has approved the use of some fuel cells in airplanes, removing what companies have called a major barrier keeping micro fuel cells out of electronic devices such as laptops and cell phones.

The department will allow passengers and crew members to carry on fuel-cell systems and cartridges that contain methanol, formic acid, certain borohydride materials and butane -- previously prohibited as flammable liquids -- as long as they meet the agency's performance and consumer-use standards. The allowed number of cartridges varies depending on the fuel, ranging between 4 and 7 ounces per person.

The decision, announced Wednesday afternoon, takes effect Oct. 1 and allows airlines to voluntarily allow the approved fuel cells as early as May 30. The cartridges would still be subject to U.S. Transportation Security Administration regulations, which only allow containers of up to 3 ounces in a single quart-size bag, according to the announcement.

But the TSA doesn’t plan to impose further restrictions, said spokesperson Nico Melendez. “It’s a hazardous material, not an explosive, so it would have nothing to do with us,” he said. “Our goal is to keep explosives and weapons off planes.”

The DOT decision is a significant step for micro fuel cells, as companies have called air travel a major potential market. After all, regular laptop batteries often run out of power – and can’t be recharged – midair, and many travelers stuck on planes say they would like to have power longer.

Fuel cells, which produce power by mixing fuel with air and water between a thin, reactive film membrane, hope to fill the so-called "power gap” caused by increasingly power-hungry devices and traditional batteries’ failure to keep pace. Instead of plugging in to recharge their batteries, users would be able to replace small fuel-filled cartridges, essentially getting an instant recharge.

Many micro fuel cell companies have pushed back their market debuts year after year, and some have blamed the delays on airplane regulations.

Toshiba, for example, in 2005 said the restrictions were the main reasons for its delay and hoped it would launch its fuel cells in 2007, when it expected the International Civil Aviation Organization to remove the prohibitions. It did, as did Canada, China, Japan and the United Kingdom, but the United States and a number of other countries continued to bar fuel cells from flight.

“Being able to fly on airplanes is a requirement for any product that claims to be a mobile product, and this decision confirms that micro fuel cells can indeed be a mobile product,” said Peng Lim, CEO of MTI Micro Fuel Cells, which plans to produce cells for handheld devices in 2009. “And that’s important because we are [selling] the functionality that you do not ever need to plug your device into a wall again. You’re spending 30 percent of the time recharging your batteries and that ties you down, it makes you not mobile.”

Ron Pernick, a principal of research firm Clean Edge, agreed that the decision is a milestone.

“If [fuel cells had continued to be prohibited in airplane cabins], I believe it would have derailed the industry,” he said. “You’ve now removed one of the most critical potential obstacles to the expansion of this industry.”

Still, that doesn’t mean micro fuel cells are ready to take flight. Years of missed promises have turned some fuel-cell believers into skeptics.

So while the restrictions were a major obstacle, they were by no means the last roadblock for the technology, Pernick said.

“Now [fuel cells] start to compete on other significant markers,” he said. “Now we’re at a point where it seems we have some clarity around the most important market and we know a road warrior can take it on a plane. But can you get enough early adopters to pay a premium? Maybe.”

Among those hurdles are cost, density (which relates to the length of time the cell cartridges can provide power) and the difficulties of getting customers to switch from familiar batteries, he said. While a small group of early adopters will pay more for extra convenience, the mainstream market will need to see cost benefits, he said, and many people think of the electricity used to recharge batteries as nearly free.

“It’s got to be equal or superior to conventional offerings, and lithium-ion is still a relatively new technology that’s being innovated on,” Pernick said. “If fuel-cell guys can hit the storage density and operational time out of the ballpark and can do it at a similar price, they have a market.”

Lim said the price for MTI’s micro fuel cells, which are aimed at handheld devices rather than laptops, will initially be higher than lithium-ion batteries, but will come down as volumes increase. He also couldn’t yet give an expected price for the replacement cartridges, but said he expects it will be competitive considering that a gallon of methanol – enough to run most consumer electronics for more than one lifetime – costs less than $1.

“In the early days, there will be a premium, but it also provides a lot of benefits,” he said. “You don’t have to bring chargers, you don’t need international wall adapters and you can recharge in any place. I really [think] people will embrace it. The value proposition for fuel cells is so high that I don’t think the price is a stopping point.”

Lim gave examples such as notebook computers and WiFi, for which people have paid more in exchange for greater freedom. In airports, particularly, people don’t want to have to be tethered to electric outlets while they are rushing to get between terminals, he said, adding that people will buy bottled water, when they can get tap water for free at water fountains and restaurants, so they can carry it with them and have it whenever they want.

The council has asked the DOT to approve additional fuels by the beginning of next year, when it also expects approval from the International Civil Aviation Organization – which approved methanol fuel cartridges last year – to take effect.