Hydrogen Sulfide In A Collection System: What We Should Know And Do To Prevent Human Injury And Sewer Asset Deterioration.

NASSCO Tech Tips
By NASSCO member Jim Harris, PE, TFE Resources | October 2013, Vol. 68 No. 10

Low concentrations of hydrogen sulfide warn us by smell, but that warning is short-lived since it quickly kills our sense of smell. Thereafter, even a few breaths of higher concentrations can cause asphyxiation and death. It is crucial that sewer workers are aware of the potential presence of this gas and are prepared to detect if this gas is present before entering a manhole. We must be especially alert if, for example, we are opening a manhole immediately downstream of a force main discharging into the main sewer or where we think the waste water flow may be slow and laminar. Properly equipped sewer inspection equipment must contain detection and safety equipment including gas detector, fresh air blower, tripod, harness, personnel removal gear, communication devices, goggles, self-contained breathing apparatus and easily accessible information regarding local emergency procedures. All of this equipment must not merely be available on the job site but must be used in accordance with confined space entry procedures. We must also warn future inspectors that propose entry to the sewer system by clearly noting on all inspection reports if hydrogen sulfide is a potential or has been detected.

In addition to safety issues, we have yet to consider the damage and costs resulting from corrosion. What can be done? First of all sewers and manholes in harm’s way can be built of non-corrosive materials. Some utility agencies, for example, build manholes that specifically include epoxy lining and install PVC pipe where the presence of hydrogen sulfide is suspected or confirmed.