Waste Water Engineering
If the flame of a miner's safety lamp in the upper layers of the sewer forms an explosive, the sewer certainly contains

Methane
Oxygen
Hydrogen sulphide
Carbon dioxide

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Waste Water Engineering
Hydraulic mean radius is

Difference in heads between two points in circular pipes
Mean radius of sewer
Cross-sectional area/wetted perimeter
Mean of radii in a pipe line of varying cross -sections

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