Now, anthrax attacks have the "industrial sterilization'' industry scrambling to see if its technology might work on something new: unopened mail.

Several companies say they're fielding calls asking whether their machines could be used in mail rooms to zap or steam away dangerous bacteria, such as anthrax. At least one says it's lining up deals to run mail through an irradiator.

Some insist the technology could be an effective way to make mail safer. But others see huge practical challenges.

"Anthrax is easy to kill,'' said Arthur Trapotsis, a scientist at Consolidated Machine Corp., a small Boston company that has been turning out steam sterilizers — essentially giant pressure cookers — for 50 years. "It's not difficult to kill a spore on paper. It's when it's in your system that it's difficult.''

For all the fear they've provoked, anthrax bacteria are vulnerable to the same weapons outside the body as other kinds of germs — namely wet heat and gamma rays. One expert has even said ironing a letter would kill anthrax spores inside, though others say it could take 20 minutes of solid, intense heat.

Last week, Trapotsis tried smearing bacteria on a stack of letters and putting them into one of the company's oven-sized units. He shut the door, infused 250-degree steam for a few minutes, and filtered out the air. The letters emerged undamaged and, according to tests, bacteria-free.

The company makes walk-in sized units that could handle more mail. But Consolidated Machine founder Bill Barnstead says he's had no customers for those steamers so far. He's sent letters to government officials but hasn't heard back.

Meanwhile, irradiation companies such as Steris Corp., based in Mentor, Ohio., and MDS Nordion, based in Ontario, say they're moving cautiously in response to calls about their irradiation devices, some of which can disinfect with a barrage of gamma rays.

MDS Nordion spokeswoman Paula Burchat says the first commercial irradiator was used in the 1960s to kill any lingering anthrax germs in lambs wool sweaters.

In Mulberry, Fla., Food Technology Service has already lined up several companies to use excess capacity at the company's irradiation facility, normally used for "truckloads'' of animal parts and fruit. The company's stock more than doubled to more than $3 in the last week before falling back below that mark Thursday.

Chief Executive Richard Hunter says deals are in the final stages to irradiate mail for several companies, at a cost of a few cents per letter.

"It doesn't change the mail, leave any stain or residue, it's not radioactive,'' Hunter says. "But it does kill any pathogens, it sterilizes.''

Numerous clients have asked the Securities Services Group at Kroll Inc., the world's largest risk consulting firm, whether such technology could protect their mail rooms, according to chief operating officer Jeff Schlanger.

"I believe it has great potential,'' he said. "We're looking into the irradiation of bulk quantities of mail.''

Biochemist Allen Louie, of Cambridge-based consulting firm Arthur D. Little, says irradiating mail raises numerous problems. Radiation, though safe to people, could damage contents, as could steam. Gamma rays could also be deflected by a metal box inside a package, and they work better in wet environments.

Furthermore, "something that's in the middle of a bundle would not get as good treatment as something toward the end of a bundle,'' he said.

But the real problems are logistical and financial. Spokesmen at several companies acknowledge the current machines, though some as large as a small room, simply aren't designed for huge quantities of mail.

"Even the big (sterilizers) couldn't do even a fraction of the amount of mail that would come through a company's mail room,'' Louie said.

The logical place to irradiate would be at centralized Post Office locations, Louie said, but that could cause delivery delays. It would be easier to irradiate only suspicious mail or mail at obvious targets, like the U.S. Capitol.

"They look like promising technologies. They're not going to be there tomorrow,'' said Postal Service spokesman Greg Frey. "In the meantime, we need to get through this.''

At Consolidated Machine, the Boston company, founder Bill Barnstead said he wouldn't be out to profit from steaming mail; a home-sized unit would cost $300-$500. Its biggest units, walk-in size, cost $100,000. For MDS Nordion's 4,000-6,000 square foot units, construction and installation costs are between $3 million and $5 million.

Numbers like that would worry the Post Office, which delivers 680 million pieces of mail per day and says it was already in financial straits before the Sept. 11 attacks.

"We welcome the technology,'' Frey said. "We also welcome anyone's idea on how to pay for the technology.''