Monday, January 14, 2013

Oooooh That Smell. Can't You Smell That Smell?

As SitePro begins our 9th year, we thought we'd start by covering one of the more glamorous topics in Real-Estate. Unfortunately, with homes sitting vacant, this noxious subject is sometimes unavoidable and can make a bad impression on an otherwise good deal. That otherwise beautiful home is emitting a smell that many buyers and agents will wrongly associate with mold, however there's often a different cause.  

With the large number of foreclosed homes sitting vacant for lengthy periods, water from the bathrooms toilets and P-Traps (that pipe under the sinks that contains water) evaporates or drains out, at which time you start getting a really unpleasant sewage smell permeating the house. The P-Trap prevents the noxious sewer gas from backing up into the house.

Sewer Gas Toilet       Sink P-Trap

What is sewer gas?


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.

How are people exposed to sewer gas?

Sewer gas can enter a home through a floor drain, from a leaking or blocked plumbing roof vent, or (if the gases are in soil adjacent to the house) through cracks in foundations.  Sanitary and farm workers can be exposed to sewer gas during the cleaning and maintenance of municipal sewers, manure storage tanks, and home septic tanks.

Note: Lines devoid of water become an avenue for Rats, Snakes and other unwelcome guests to enter the dwelling.

What are the effects of exposure to sewer gas?

The principal risks and effects associated with exposure are:
  • Hydrogen sulfide poisoning. Exposure to low levels of hydrogen sulfide causes irritation of the eyes and respiratory tract. Other symptoms include nervousness, dizziness, nausea, headache, and drowsiness. This gas smells like rotten eggs, even at extremely low concentrations.  Exposure to high concentrations can interfere with the sense of smell, making this warning signal unreliable. At extremely high levels, hydrogen sulfide can cause immediate loss of consciousness and death.
  • Asphyxiation. High concentrations of methane in enclosed areas can lead to suffocation as large amounts of methane will decrease the amount of oxygen in the air. The effects of oxygen deficiency include headache, nausea, dizziness and unconsciousness. At very low oxygen concentrations (<12%), unconsciousness and death may occur very quickly and without warning.  Sewer gas diffuses and mixes with indoor air, and will be most concentrated where it is entering the home.  
  • Explosion and fire. Methane and hydrogen sulfide are flammable and highly explosive.

How can you 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 you do if you suspect a problem?

First, following the odor, try to locate the point of entry, such as a 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.  In the unlikely event that a leak in gas vent plumbing is behind walls, a plumber may be needed to find and fix it.  

Symptoms of headache, nausea, dizziness, or drowsiness may indicate exposure to an odorless gas like methane or carbon monoxide, or to hydrogen sulfide, which smells of rotten eggs.  Persons experiencing severe symptoms should seek immediate medical care.

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.

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