A potentially fatal lung disease linked to chemicals used in food flavorings poses a growing health risk, according to government scientists who are questioning the food industry's willingness to protect its workers.

Bronchiolitis obliterans first emerged as a threat within the food industry in 2000, when the National Institute of Occupational Safety and Health was called to a southwest Missouri popcorn plant to investigate lung illnesses among workers.

Investigators subsequently found the disease among popcorn workers throughout the Midwest. They linked it to diacetyl, a substance that is found naturally in many foods but which also is artificially produced and widely used as a less expensive way to enhance flavor or impart the taste of butter.

NIOSH has linked exposure to diacetyl and butter flavoring to lung disease that sickened nearly 200 workers at popcorn plants and killed at least three.

"Now we've got cases of bronchiolitis obliterans among workers in other plants that use flavorings and in plants that make the flavorings," said Dr. Kathleen Kreiss, chief of the field studies branch of NIOSH's division of respiratory disease studies.

Bronchiolitis obliterans causes inflammation and obstruction of the small airways in the lung by rapid thickening or scarring. The irreversible condition is progressive and often fatal without a lung transplant.

Recent cases that NIOSH scientists have learned about include a man who worked at a small Baltimore-area flavoring company, a man who worked at a North Carolina potato chip plant, and an employee at a Chicago candy maker, and workers at a Cincinnati flavoring plant.

"We need to get into some of these plants because we don't have confidence that the flavoring industry has taken steps to actually prevent this disease, and we need to determine how widespread the exposure may be," Kreiss told The (Baltimore) Sun.

But while scientists at NIOSH and the Occupational Safety and Health Administration want to intensify investigations, agency leaders say they don't plan to act because they believe enough is being done now.

"OSHA advises its inspectors that workers may be at risk of overexposure to vapors of artificial flavorings in a variety of food processing work sites," said Al Belsky, a Labor Department spokesman.

"There is nothing to indicate that additional regulations are needed," Belsky added.

David Michaels, an epidemiologist at George Washington University's School of Public Health who examined OSHA's handling of the popcorn workers' sickness, called its inaction "criminal."

Meanwhile, the Food and Drug Administration has allowed flavoring producers and sellers to decide which chemicals are safe, and California's occupational safety agency has delegated health examinations of flavoring workers to an industry-paid doctor.

The difficulty of assessing workplace illness is further complicated by employees who fear reprisal for complaining about hazards and by physicians who lack the training to recognize bronchiolitis obliterans and other occupational threats.

About 70 U.S. companies are involved in the making and sales of flavorings, according to the Flavor and Extract Manufacturing Association, the largest trade group for the $3 billion-a-year industry. Of more than 8,000 employees, only about 3,000 are engaged in the actual production of flavorings. In the much larger food processing industry, however, tens of thousands of workers are estimated to work with flavorings.

More than 150 former popcorn plant workers have sued companies supplying or making the butter flavoring, and more than $100 million has been awarded in jury verdicts or paid in settlements. At least 30 suits are still pending.

The latest suit, filed in February, charges that the Flavor and Extract Manufacturing Association conspired with the other defendants to fraudulently conceal information about the health risks of butter flavoring.

"There is no conspiracy," said John Hallagan, the trade association's lawyer and former science director.

In 1985, consultants for the trade association produced a data sheet indicating that breathing diacetyl is harmful to the respiratory tract and is "capable of producing systemic toxicity."

Hallagan said his organization has cooperated with government scientists, held workshops for its members, and issued an August 2004 report on respiratory health and safety that remains on its Web site.

"I'm not sure what more we could have done to get the word out," he said.