Civil Engineering

Precautions to be Taken While Entering Sewers

Various poisonous and explosive gasses are commonly found in sewers such as hydrogen sulphide (H2S), carbon dioxide (CO2) and methane (CH4) along with petrol vapours. These gases are produced largely when the sewage becomes stale and septic, which occurs more commonly in hotter climates.

Precautions to be Taken While Entering Sewers
Precautions to be Taken While Entering Sewers

In addition to the production of these harmful gases, oxygen is consumed by the organic matter for their decomposition, resulting in a lack of oxygen inside the sewer and can, therefore, cause difficulty in breathing.
Various methods are adopted for ventilating the sewers in order to avoid the large scale presence of these poisonous and hazardous gases inside the sewers. In addition to the ventilation of sewers, the following precautions should also be taken while allowing the workers to enter the sewers

1. The very first precaution which should be taken before entering a sewer through a manhole is to open the covers of the manholes; at least half an hour in advance. This will help in obtaining some ventilation and exposure of the sewer to the atmospheric oxygen.

2. Tests should be conducted in order to identify the presence of any harmful gases inside the sewer. The following tests may be carried out to detect their presence.

  • The first test is performed to detect H2S gas present in the sewer.
  • The second test is performed to detect CO2 gas present in the sewer.
  • The third test is performed to detect CH4 gas present in the sewer.

3. If the above hazardous gases are absent, a lighted lantern may be lowered down the manhole, so as to test the presence of oxygen. If it burns brilliantly, the sewer can be safe to enter.

4. In any case,  the staff who go down into the sewer for inspection must be bound to their waists with ropes and hold them fast by persons on the top so that they can be pulled up quickly in case of any risk. A responsible officer should be available to handle the operations perfectly.

5. It is strictly prohibited to smoke or bring open light inside the sewers.

6. Necessary indicators of alert should be set up.
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