Various gases are produced in sewers due to purification of organic materials of sewage. These gases are very foul in nature, cause harmful to human health and corrode the sewers. The gases so produced are highly explosive and may cause accidents. Due to the above difficulties, the sewers must be properly ventilated. The following methods are adopted for ventilating the sewers:

1) Use of ventilating columns : The ventilating shaft is provided along the sewer line at an interval of 150 m to 300 m. They are also provided at the upper end of every branch sewer and at every points where sewer diameter changes. Ventilating shaft helps to remove the foul and explosive gases produced in the sewer. They provide fresh air to the workers working in the manholes. They also help to prevent the formation of air locks in the sewage and thereby ensure the continuous flow of sewage inside the sewer.

2) Use of ventilating manhole covers: The manhole covers are sometimes provided with perforations, through which the sewer gets exposed to the atmosphere. This will help in achieving some ventilation, but will cause more nuisances.

3) Proper design of sewers: The proper design of sewers also ensures enough ventilation.

4) Use of mechanical devices: Forced draught is sometimes provided by exhaust fans to expel out the foul gases from the sewers.

5) House vent and soil pipes: They may directly help in ventilating house drains and public sewers.

6) Artificial ventilation: Sometimes artificial ventilation is arranged at site before entering a sewer, by blowing fresh air supply into the sewer though mechanical means.