Michigan Homes And Sewer Gases

Reblogger Donald Horne
Real Estate Broker/Owner

This article on sewer gases is eye opening. I never knew how many different gases were in the sewers. Hope this post comes in handy if your experiencing some of these problems.

Original content by Jason Channell

Michigan Homes And Sewer Gases

Did you ever have a yucky smell coming from your drain? You just might have a problem with sewer gases.


When waste in sewer or septic systems decompose, they create sewer gases, which can have a really nasty impact on a resident's health.

Sewer gas is a complex mixture of toxic and non-toxic gases that can be present at varying levels depending upon the source.  It is formed during the decay of household and industrial waste. Highly toxic components of sewer gas include hydrogen sulfide and ammonia.

Sewer gas also contains methane, carbon dioxide, sulfur dioxide, and nitrous oxides. In addition, chlorine bleaches, industrial solvents, and gasoline are frequently present in municipal and privately owned-sewage treatment systems.


Hydrogen Sulfide Poisoning

Hydrogen sulfide is an explosive and extremely toxic gas that can impair several different systems in the body at once, especially the nervous system.

It can be smelled at 0.47 parts per billion by 50% of the population, but it won't begin to cause eye irritation until the concentration reaches 10 parts per million (ppm). Eye damage ensues at 50 ppm, as do other symptoms like nervousness, dizziness, nausea, headache and drowsiness.

Exposure to higher concentrations can lead to pulmonary edema (fluid accumulation in the lungs that leads to respiratory failure), and still higher levels (800 to 1,000 ppm) will cause almost immediate loss of consciousness and death.


Methane Gas

By itself, methane is not toxic. It is extremely flammable and will cause an explosion; it will also kill you by asphyxiation if it leaks into an enclosed space and deprives you of oxygen. But methane only becomes poisonous when it forms part of another gas.



Sewer gases diffuse into household air and gradually displace oxygen. As this happens, the gases suffocate the occupants.

The effects of oxygen deficiency include headache, nausea, dizziness and unconsciousness. At very low oxygen concentrations (less than 12%), unconsciousness and death will occur quickly and without warning. Oxygen will be at its lowest concentrations in the basement, which is where heavy sewer gases are likely to collect.


Fire Or Explosion

Methane and hydrogen sulfide are explosive components of sewer gas. Vapors from improperly disposed fuel can further increase the risk of fire or explosion.


Maybe not as dangerous a problem, but still incredibly unpleasant.

Hydrogen sulfide is responsible for sewer gas’s characteristic rotten-egg smell, which can be overbearing even at extremely low concentrations. But on the bright side, the strong odor alerts occupants to the leak long before they’re in any serious danger.

It is important to note that at roughly 100 ppm, the olfactory nerve becomes paralyzed, removing the victim’s sense of smell and, subsequently, their awareness of the danger.

Another "warning smell" comes from ammonia, which will sear the nostrils and progressively irritate the mucous membranes and respiratory tract. This gas, unlike hydrogen sulfide, is sufficiently irritating that building occupants are likely to vacate before its concentration rises to toxic levels.


Possible Causes

Dried-out piping and pluming fixtures
In most cases, intruding sewer gases are caused by a loss of the water barrier where traps have gone dry. Infrequent use of a toilet, shower or floor drain can allow for rapid evaporation and entry of sewer gases into the living space.

Particularly common culprits are floor drains placed in locations where they are likely to dry out, such as near water heaters or furnaces, or in commercial buildings around janitor’s closets, workshop areas and mechanical rooms.

Homeowners can maintain the water barriers by using the fixtures more often or by pouring water down the drains. Automatic drain-trap primers may also be installed so that a small amount of water is periodically delivered.

Cracks In The Line
A water leak typically accompanies a crack in the drain line, but vent pipe cracks are more difficult to diagnose, and they can vent a large quantity of sewer gases into the home.

Plumbers can locate these cracks by using a special machine that generates artificial smoke and pumps it into the plumbing drain system. The smoke pressurizes the system and exits through any cracks or loose fittings.

Plumbing Vents
Plumbing vents installed too close to air intakes or windows in homes equipped with HVAC air handlers that admit outside air for ventilation. Wind and air flow around the building can allow for sewer gas to enter the building even where plumbing vents and air intakes are appropriately placed. Homeowners can add vent pipe filters or alter the height of vents to alleviate the problem.

Other Possible Causes:
  • diffusion from a leach field septic system
  • through cracks in a building’s foundation

How can I avoid being exposed to sewer gas?

  • Flush floor and sink drains with water to prevent the traps in pipes to the sewer from drying out.

  • Occasionally check the roof plumbing vent for blockage from debris such as leaves or bird nests.

  • Never enter a municipal sewer line, manure-storage tank or any other large storage tank without proper training and equipment.


What should I do if I suspect a problem?

If you suspect that any odors might be caused by sewer gases, contact a licensed and qualified plumber.

If you want to investigate the problem yourself, follow the odor and try to locate the point of entry, such as a basement floor drain. Check for a blocked rooftop plumbing gas vent.

By adding water to the floor drain or removing debris from a roof plumbing stack vent you may be able to prevent sewer gas from entering your home. 

If you suspect that high concentrations of sewer gas have accumulated in an enclosed space, you should evacuate the area and contact the fire department for assistance.  Avoid creating an ignition source such a spark from an electrical appliance, match, or cigarette lighter.


In Conclusion

The design of the plumbing system relies on a connection between household fixtures and the sewer system, which is why a great deal of effort is spent to ensure that waste products -- and the gases that result from their decay -- flow in one direction.
These failures in the plumbing system may allow sewer gases to flow back into a building.



Jason Channell, The House Sleuth

(888) 699-8710

Learn more: Indoor Air Quality and Environment

Learn more: Maintaining Your House


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Dan Edward Phillips
Dan Edward Phillips - Eureka, CA
Realtor and Broker/Owner

Good Morning Donald, excellent post on sewer gases, thanks for putting it back up.

Dec 23, 2010 09:02 PM #1
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