What are wet wells?
Pump stations are home to wet wells, which are large, open holding tanks in which wastewater is pumped from municipal sewer lines and held prior to treatment. It is here that heavier solids are left to sink to the bottom while lighter solids float to the top for removal before the remaining wastewater is pumped for secondary treatment.
Naturally occurring combustible and toxic gases are ever present in varying quantities during this process. Though typically invisible, these gases can emit a pungent or “rotten egg” odor that’s often deceiving in terms of their potentially lethal nature for both combustibility and toxicity.
Combustible and toxic gas detectors can be used to alert system operators whenever the intensity of these noxious gases intensify to the point of being a serious fire hazard or respiratory threat to workers.
Additionally, the wet wells environment also holds the potential to create oxygen (O2) deficiency conditions, especially in confined spaces; yet another reason to employ fixed gas detectors within these areas.
NFPA Code 820 is a standard for fire protection in wastewater treatment and collection facilities, including pumping stations, chemical- and sludge-handling facilities, and ancillary structures. The standard is designed to protect life, property, operations, and the environment from fire and explosion hazards.
At a minimum, NFPA 820 requirements include:
- Reducing or eliminating the effects of a fire or explosion
- Maintaining the structural integrity
- Controlling flame spread and smoke generation
- Preventing the release of toxic products of combustion
- Ensuring serviceability and operation of the facility
The standard specifically calls out three separate process areas related to combustible gases:
- Collection Areas
- Liquid Streams
- Solids Treatment
Wet well monitoring falls under the Liquid Streams process area of the standard. In general, the standard for this process area requires a variety of fire protection materials, including a combustible gas detection (CGD) system. Please see the current edition of NFPA 820 for the exact details for combustible gas detection monitoring, including the Liquid Streams process area of the standard.
Maintaining Compliance with a Combustible Gas Detection System
This article has been reposted from MSA’s blog:
“Wastewater Treatment: Why Monitoring Wet Wells Is Crucial to Staying Compliant with NFPA Code 820,” MSA Safety: Spotlight on Safety. [Online] Available: https://blog.msasafety.com/fgfd-wastewater-treatment-why-monitoring-wet-wells-is-crucial-to-staying-compliant-with-nfpa-code-820/