I just received this alert bulletin and thought it was of interest:

"As a result of the heavy rainfall over the last few weeks several contributing factors are coming together that is resulting in dangerous atmospheric conditions, particularly in below grade levels of dwellings.

The recent rainfalls have saturated the top layer of soil, down several feet. The water table also continues to rise toward the surface. As is always the case, Methane (natural gas) and Carbon Dioxide exist in soil as a result of the natural decomposition process.

The result of water pushing down and water pushing up is that the naturally occurring gases - Carbon Dioxide and Methane - are being squeezed out of the soil and pushed down (or up) the path of least resistance. This path has resulted in these gases making their way into sumps and other below grade accesses inside dwellings (they only present a hazard when confined, so although they are being pushed to the surface in other areas, they do not generally pose a threat.

MDE has reported several incidents across the region, and two incidents in Howard County, where Carbon Dioxide and Methane have created an unsafe atmoshpere in the basements of dwellings. What responders are being called for is residents experiencing shortness of breath, headaches or burning sensations of the mucous membranes. Responders typically find decreased levels of oxygen (caused by the presence of Carbon Dioxide in large quantities - >30,000 ppm in some instances) and positive LEL readings (caused by the presence of Methane) using a four gas meter.

Methane, under these circumstances, is colorless and odorless as it does not contain the additive mercaptan. Methane is lighter than air and is a flammable gas.

Carbon dioxide is also colorless and odorless. Carbon Dioxide is heavier than air and is non-flammable. Exposure to high levels of Carbon Dioxide can result in headache, dizziness, restlessness, paresthesia, dyspnea, sweating, malaise, as well as an increased heart rate and blood pressure.

During the next few weeks, while the water table remains high and the ground is saturated with water, if you respond to an incident where residents are exhibiting any of the symptoms listed in the absence of other medical explanations you should strongly consider the phenomenon described above. Particularly if the resident is in or has been in a below grade level.

Check below grade levels of the home with a four gas meter. If you detect LEL readings accompanied by decreased levels of oxygen you should evacuate the residence and request Special Operations for further investigation. A standard four gas meter cannot distinguish between methane and other flammable vapors."

Pete