When microorganisms break down solid wastes in your sewer, the process inevitably produces hydrogen sulfide, a strongly odorous and potentially harmful gas. This gas is normally contained in plumbing underground where it cannot harm anyone above ground. But through a variety of means, hydrogen sulfide -- or "sewer gas" as it is sometimes called -- can escape and make its way into many different parts of the home.
Tracing a Sewer Gas Leak
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Sewer gas is distinguished by its instantly recognizable rotten egg smell. Though the smell is offensive, it can provide easy means for tracing the source of the sewer gas leak. If you smell sewer gas in your closet, there could be a leaking plumbing pipe underneath the closet or behind the wall, or a toilet seal could be broken in a nearby bathroom and the sewer gas wafting into the closet. Identifying the source of the leaking sewer gas is the first step to resolving the problem.
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Repairs
Once you have identified the source of the leaking sewer gas, it is important to have a plumber repair the leak right away. At high enough concentrations, sewer gas can cause human health symptoms ranging from minor irritation to memory loss and death; while it is unlikely that a single sewer gas leak would produce enough gas to cause these symptoms, hydrogen sulfide is explosive and flammable, and its offensive odor will persist for as long as the leak goes unrepaired.
Possible Hazards of Sewer Gas
Sewer gas is mostly hydrogen sulfide, but it can also include methane and other gases. Low level hydrogen sulfide poisoning causes eye and respiratory irritation; high concentrations can cause loss of consciousness and death. High concentrations of methane in an unventilated area can cause asphyxiation by diluting the amount of oxygen in the room. The smaller the enclosed area, the more quickly methane can deplete oxygen levels, so limit the amount of time you spend in the closet when it is full of leaking sewer gas.
Other Considerations
Though less common, there are several reasons other than clogged plumbing that sewer gas could build up inside your closet. If your home uses a septic system, parts of the system can freeze during the winter and cause sewer gas to back up into the home. Once the septic system thaws, it should return to normal working order and the sewer gas should subside.
Improperly installed toilet gaskets can allow sewer gas to seep up into the bathroom and surrounding rooms even if the plumbing underneath the toilet is not damaged; the latter is more easily remedied by simply reinstalling a toilet gasket in the proper manner.