19 Dec 2019
Sewer Odour

Do you smell something that seems to be sewer gas, and smell like rotten eggs in and around your bathroom area?
This could be caused by a problem with your house / building plumbing work.Properly constructed and maintained plumbing will prevent sewer smells from entering into living and habitable environment.

The plumbing system inside any building structure consists of a network of pipes, vents & traps. The sewer pipe system of branching pipes that carry off liquid and solid wastes is just as important as the actual water supply piping system.

Each plumbing fixture (toilet, sink, shower, floor drain, etc.) is connected to the sewer piping that carries the wastewater to the municipal drainage network. This system safely removes sewage from individual residence and provides a critical barrier that is designed to keep sewer gases out from entering to individual user premises.

What is a Sewer gas ?
Sewer gas is a generic name for the collection of gases and airborne agents that often accompany sewage and the natural processes and reactions associated with sewage processing and the decomposition of organicmaterials. The major components of sewer gas can include: Hydrogen Sulphide (H2S), Carbon Dioxide (CO2), Methane (CH4), Ammonia (NH3), biological organisms, water vapour, and other chemicals. The presence and concentration of any of these components can vary with time, composition of the sewage, temperature and pH.

  • Hydrogen Sulphide’s concentration in the gas phase is dependent upon its concentration in the liquid phase and ambient equilibrium conditions. At non-toxic levels, H2S has the familiar odour of rotten eggs. At acutely toxic levels, H2S quickly paralyses an individual’s ability to detect its odour, and will rapidly render a victim unconscious.
  • Carbon Dioxide and Methane have little or no odour characteristics and have a saturated gas density approximately 1.5 and 0.6 times that of air, respectively.
  • Methane is extremely flammable, has a wide explosive range and a low flash point. These characteristics result in a substantial fire and explosion hazard.
  • Ammonia has a distinct, strong odour with good warning characteristics which are present well before attaining toxic levels.
Vents and Traps

Significance of Vents and Traps ?

  • Traps hold enough water to block sewer gases from entering the habitable space.
  • Traps in each fixtures should be properly vented to maintain water seal in its place.
  • Vents allow sewer gases to flow up the vent pipe and exit the system without entering your home through plumbing fixtures.
  • Venting system allows outside air into the drain piping system to keep vacuum from forming in the drain pipes, which allows proper drainage within the piping network.
  • Poor venting arrangements can create either +ve pressure (more than atmospheric pressure) in the drain line, which may lead to water seal to blow-off in the traps of the drain fixtures or -ve pressure(less than atmospheric pressure) in the drain line, which may create siphonage in the traps of drain fixtures.

Possible causes of sewer smell:

There are a variety of reasons that sewer smell may be entering in to a living space. These include following:

  • The most common reason is either the lack of required traps or vents, or their malfunctioning. It’s very important that every fixture should have a trap which should be properly vented to protect the water seal to keep sewer gases out from entering into living space. If traps and vent pipes are missing, one need’s to install them immediately.
  • Another cause of indoor odour is due to clogged vent. Bird nests, leaves and pests are some common causes. In this case one must disconnect the vent pipes from inside the home and clean them all the way through the roof and vent cowls are to be placed on the top of every drain & vent lines along with mosquito mesh for added layer of protection.
  • A frequent cause for indoor odour is due to a dry trap. The water in the trap seal may evaporate due to heat over time, allowing to enter sewer gas into living space.Pouring a mug full of water into all sinks, showers/tubs and floor drains may correct this problem OR you may simply install trap primer which will maintain the water seal in the trap of the fixture and prevent the backflow of sewer gas.
Trap Primer

Note: Trap Primers are mandatory on all emergency drains as per code.

  • The trap under the basin may not be holding enough water and is allowing sewer fumes into the living space. UIPC doesn’t promote the usage of bottle trap since, it can’t assure a minimum 50 mm water seal which is a prerequisite as per the Uniform plumbing code.
Bottle Trap

Note: P- type traps are code approved traps for basin drain.

  • It is possible to have a crack or leak in one of the vent lines of the plumbing system or a leak around the base of a toilet or other fixture. one needs to check for loose fittings, corrosion or holes in vent piping andthe top side of horizontal drain pipes. If the top portion of the pipe is rusted, it may not leak liquid but it will allow to escape sewer gas. Any drain lines made of metallic material may exhibit this problem.
  • Improper A/C drain outlet connection – Its has been observed on various sites that many a times, A/C drain pipes are connected to its nearest possible plumbing pipe (waste pipe, vents pipe or even soil pipe) without even consulting the professional plumbing engineer / consultant. In such case, whenever the A/C unit is turned on, it sucks the sewer smell from drain pipes (due to air pressure differential and missing trap and water seal arrangement) and blow it all across the entire room.
  • Gully Chamber is located at the bottom of the waste pipe stack and right before connecting it to the internal drainage network, Gully Chamber has PVC or Stoneware P-type trap which acts as a defence line for preventing the entry of foul smell, insects into the building. If the Gully chamber is broken or cracked, the water seal in the trap will not be retained and the foul smell and gasses can enter in the building premises.
  • Sewer trap are installed on the last internal drainage chamber located within the building plot area and before connecting it to the municipal drainage network. If the Sewer trap (which is the last defence line) is damaged / cracked then it will allow foul smells and gasses to seep in through the cracks and into the building plot area.
Sewer Smell IPT Nov 2019

Conclusion: Drains seem to work even without properly installed or operating traps and vents. Many plumbers, labours and even local contractors do not consider these components and do not understand their importance. But it’s our duty as a responsible Plumbing Engineer & Consultant to follow correct plumbing practices for better human sanitation.