The main odor causing gas in manholes is Hydrogen Sulfide. Monitoring the H2S levels above and below the Manhole Odor Eliminator, shows the effeciency of the filter as well as any servicing or other issues. Manholes with high concentrations of Hydrogen Sulfide can be fitted with larger capacity filters.
Typical installation showing untreated and treated H2S concentrations. Click here for larger view.