The Environmental Protection Agency (search) is studying the chemicals released into the air when a bag of microwave popcorn is popped or opened.

Exposure to vapors from butter flavoring in microwave popcorn has been linked to a rare lung disease contracted by factory workers in Missouri, Illinois, Iowa and Nebraska. The National Institute for Occupational Safety and Health (search) has said it suspects the chemical diacetyl caused the illnesses.

However, health officials insist people who microwave popcorn and eat it at home are not in danger.

In the first direct study of chemicals contained in one of the nation's most popular snack foods, the EPA's Indoor Environment Management Branch (search) at Research Triangle Park, N.C., is examining the type and amount of chemicals emitted from microwave popcorn bags.

Further research would be needed to determine any health effects of those chemicals and whether consumers are at risk, said Jacky Rosati, an EPA scientist involved in the study.

"Once we know what chemicals are and the amounts, somebody else can look at the health effects," Rosati said Wednesday.

About 50 brands, batches and flavors of microwave popcorn — from super-buttery to sugary sweet "kettle corn" — are being tested, she said.

"Obviously, we are looking at diacetyl because it is a known compound that will come off this popcorn. But we're not looking at that alone," Rosati said.

The EPA study began last fall and is expected to be completed this year. It likely will be submitted for peer review before being made public, Bob Thompson, acting branch chief of EPA's Indoor Environment Management Branch, said.

Rosati started the study after hearing a presentation on popcorn workers who became sick at the Gilster-Mary Lee Corp. plant in Jasper, Mo.

The National Institute for Occupational Safety and Health has linked diacetyl to the respiratory illnesses found in workers who mix the microwave popcorn flavorings. Investigators believe the chemical becomes hazardous when it is heated and there is repeated exposure to large quantities over a long time.

Thirty former workers at the Jasper plant have suing two butter flavoring manufacturers.

The Flavor and Extract Manufacturers Association based in Washington, D.C., said the flavor ingredients in microwave popcorn pose no threat to consumers.

The Food and Drug Administration, which regulates food additives, also considers butter flavoring to be safe for consumer use.

"I haven't seen anything that would give us any reason to suspect this is something we should make a high priority," said George Pauli, acting director of the FDA's office of food additive safety.

United States consumers bought $1.33 billion worth of microwave popcorn in 2000, said Ann Wilkes, spokeswoman for the Snack Food Association.