When Racal Airstream Inc. set up headquarters in Rockville, no one expected the State of Washington to be a major market. That was before Mount St. Helens erupted, whirling volcanic ash several times across most of that state and others.

Racal Airstream Inc. of Rockville makes the Airstream helmet, a space-age variation of the gas mask that combines hardhat, mask and respirator. The helmet draws and purifies contaminated air through a series of filters, passing the clean air over the face behind the clear visor. It slips on easily, warding off the effects of dust and pollution associated with industry, mining and agriculture.

Airstream officials said the firm donated about $50,000 worth of equipment and supplies to agencies in Washington State.

The equipment was being used by emergency crews, law enforcement officials and clean-up teams within days of the first eruption. By then, Airstream general manager Kenneth V. Vaughan had organized a team of engineering and technical experts to work in Yakima, Wash., and Portland, Ore.

Vaughn said the masks protected rescue workers from the heavy concentrations of chalk-like dust and ash from the volcano.

Doug Blackmore, a deputy sheriff in Ellensburg, Wash., said he wore one while maintaining roadblocks.

"I had been using a disposable mask, but the Airstream was fantastic," he said.

"Thank God they came out here with that thing," said Doug Martensen, a operator of a trash compactor at the Kittitas County landfill. "I was having severe chest pains. My lungs were on the way out. I got my helmet five days after the blast and I've worn it ever since!"

Baughan emphasized that the firm's main concern was to "help the people in any way we could," not to profit from the disaster.

But since then, encouraged by the success in Washington, Vaughan and Harry H. Herman, consulting director of Airstream, have begun to market the product to emergency services elsewhere in the country.

The helmet was designed by the firm's parent company, Racal Electronics Ltd. of London, for use by the British Bureau of Mines. For the past eighteen months, Vaughan and Herman, who are engineers, modified the helmet at their Rockville site to meet federal standards.

The helmut won first place in the 1978-1979 Engineering Excellence Awards Program sponsored by the Consulting Engineers Council of Metropolitan Washington.