One morning earlier this winter, Bishop and Rodgers were at the state Capitol trying to get some traction for their concerns. After trying unsuccessfully to get an appointment with Attorney General Mark Shurtleff, they ran into two members of the Bountiful City Council. Both Rodgers and Bishop live in Bountiful, so they were happy to see some friendly faces.

Bishop, who has a Ph.D. in chemistry, spent 20 years at the Tooele Army Depot, helping the military meet the requirements of the Environmental Protection Agency. Like Rodgers, his father was in the heating business. Rodgers, who once was a cattle rancher but now is a vegan, once worked as a pathologist.

"We're poisoning babies, right now, today," Rodgers told the Bountiful council members as they stood in the hall outside the attorney general's office. It's a sentiment Rodgers uses repeatedly. "We have dead people and sick people," he'll often say to anyone who will listen. All winter long he has walked the halls of the Capitol, trying to get the attention of lawmakers.

Rodgers and Bishop want the news media to alert the public so that people living in HUD homes can take some immediate temporary measures to solve the problem, and they want state governments to pass regulations to solve the problem permanently. They predict that HUD will never admit its code is dangerous.

Pressed for details, however, both Rodgers and Bishop have no hard data to prove that anyone has been killed or injured as a result of the HUD venting design.

Here's the problem: The lack of evidence could mean there have been no deaths or injuries, but it also could mean that carbon monoxide is a stealthy gas that produces symptoms so vague — flu-like headaches and nausea, chest pain, dizziness — that the people affected, and the doctors who treat them, don't blame the right culprit.

Hospitals do not routinely test for carbon-monoxide poisoning, so it's hard to get data. And low-level, chronic carbon-monoxide poisoning is even harder to detect than acute carbon-monoxide poisoning. Symptoms include depression and memory impairment, in addition to flu-like problems, according to David G. Penney, a professor at Wayne State University and an expert on carbon-monoxide poisoning.

The poisoning "is more often missed than found," says Penney. "It's not something physicians are trained in." A yearlong Rhode Island study published in 2008 in the Journal of Emergency Medicine, based on carbon-monoxide screenings of all emergency-room patients, estimated that as many as 11,000 cases of low-level carbon-monoxide poisoning go undetected each year in the United States.

"Chronic CO poisoning is often misdiagnosed as chronic fatigue syndrome, a viral or bacterial pulmonary or gastrointestinal infection, a run-down condition, immune deficiency, etc.," writes Penney on his Web site coheadquarters.com.

CT scans and MRIs generally show no lesions, he says, "even when neuropsychological and/or neurologic evaluations may detect functional deficits."