The report details the investigation into a West Virginia couple's unexplained maladies -- from blurred vision to breathlessness to "episodic mild confusion" -- that authorities now believe stemmed from heightened carbon dioxide levels in the couple's finished basement and its adjacent crawlspace.

Perhaps the most chilling accounts were those describing a rush of air when the door to the crawlspace was opened. One firefighter, according to the NIOSH report, "felt a strong draft at the crawlspace entrance that 'took his breath away.'"

Paranormal activity? Not exactly. After investigations by the homeowner, a hired contractor and firefighters yielded few clues as to what was causing the rash of symptoms, authorities from county, state and federal health agencies descended upon the West Virginia home to conduct further tests.

The results were nearly as macabre as a campfire story.

The West Virginia Department of Environmental Protection detected carbon dioxide concentrations as high as 9.5 percent in the basement crawlspace. The carbon dioxide (CO2) level in normal air is around .035 percent, according to NIOSH, and NIOSH's recommended exposure limit for 15 minutes is 3 percent. A level of 4 percent is designated by NIOSH as "immediately dangerous to life or health."

(NIOSH's recommended exposure limits for CO2 in the workplace is .5 percent, or 5,000 parts per million, for a 40-hour workweek.)

Authorities detected CO2 levels as high as 11 percent in the crawlspace gravel and 12 percent in the basement floor drain of the West Virginia home, according to the NIOSH report. CO2 levels in the soil surrounding the home were as high as 8 percent.

Could a ghost somehow be to blame? Actually, authorities, after further testing and investigation, say the most likely source of the excess CO2 was mining -- the house was built on a reclaimed surface coal mine, and an abandoned deep coal mine lies beneath the property, according to the report.

The risks of elevated CO2 levels

The West Virginia couple has since made renovations to the crawlspace to remedy the problem of CO2 infiltration into the home, but the report should still serve as a cautionary tale for indoor workers, public utility employees, emergency response officials and remediation workers in mining areas, according to NIOSH.

"The fact is this can happen in workplaces as well as homes, and not just above mines," said Lisa Benaise, MD, MPH, an epidemic intelligence service officer in NIOSH's Division of Respiratory Disease Studies, based in Morgantown, W.Va. "Landfills and caves also have CO2 emissions, and there are other areas under buildings that can have these kinds of emissions. It's very serious. We don't know how big the problem is, especially with mines because a lot of mines were built more than 100 ago when, by law, they did not have to be reported."

The potential health effects of exposure to CO2 levels between 2 and 10 percent, according to Benaise, include: headache; increased heart rate; dizziness; fatigue; rapid breathing; and visual and hearing dysfunctions. Exposure to even higher levels can lead to unconsciousness or death within minutes of exposure.

Public utility workers, first responders and health providers, according to the NIOSH report, "should be aware of the risk of incapacitation or death from oxygen deficiency and carbon dioxide toxicity when occupants of buildings in areas with reclaimed or abandoned coal mines complain of shortness of breath, palpitations, dizziness or confusion of have difficulty maintaining their pilot lights."

Bringing 'black damp' above ground

Coal miners, Benaise said, in the old days used to call it "black damp" when the flame from a lamp or candle died -- presumably snuffed out by low oxygen levels and possibly elevated CO2 and nitrogen levels.

"When the oxygen level was insufficient to keep the flame alive, they knew it was time to get out of the mine," Benaise said.

While miners already are aware of the dangers of elevated CO2 levels in confined spaces, the results of the NIOSH report underscore the need for a more widespread public awareness of this hazard, Benaise said.

"First responders generally check for methane, carbon monoxide and other explosive gases, but they don't check for carbon dioxide," Benaise explained. "If they detect low oxygen levels, they need to consider the possibility that elevated CO2 levels exist."

NIOSH recommends careful measurements of suspect environments to assess potential risks, but Benaise said CO2 detection equipment is too expensive for some agencies to have on hand. If CO2 meters aren't available, and oxygen levels in a suspect area are low, she suggested testing for other gases such as methane and carbon monoxide.

"If those other gases are low or below detectable limits, then they should have carbon dioxide on their list of potential risks," she said.

The NIOSH report also recommends:

  • Special training for emergency response and utility workers;
  • Indoor workers taking precautions to avoid incapacitation and making preparations for rescue during immediately dangerous situations;
  • Building codes that mandate preventive construction, including scaling cracks, maintaining positive pressure within the structure and subsurface ventilation for new buildings over landfills, caves and abandoned mines.