Gas Detection in Wastewater Treatment and Collection Facilities
Complete RC System's ZoneProtector gas detection system
NFPA 820 details requirements for protection at wastewater treatment facilities and collection facilities.
Gas Detection and Alarm Requirement from NFPA 820
NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities, establishes minimum requirements for protection against fire and explosion hazards in wastewater treatment plants. The requirements shall apply to new installations, additions, or modifications made to existing facilities. The requirements shall be used by owners in a risk assessment to identify the areas of a treatment plant that are vulnerable to fire or other loss. Combustible Gas Detection, primarily for Methane (CH4), is required in many areas. Hydrogen Sulfide (H2S) and Oxygen (O2) monitoring are also frequently used. Methane Gas detection points are placed near the roof of a structure. Oxygen and Hydrogen Sulfide detection points are usually placed in the breathing zone for personnel protection. Alarm Signaling for combustible gas detectors and ventilation are mandated by NFPA 820.Ventilation Requirement from NFPA 820
Most semi-enclosed and enclosed process areas in wastewater treatment facilities are classified as Class I, Division 1 or Division 2, Group D. Proper ventilation of an area may reduce classification to Division 2 or non-classified. Refer to NEC Article 500 and NFPA 496 for more information. NFPA 820 requires that all the ventilation of the hazardous location needs to be monitored.Collection Systems’ Locations (from NFPA 820 Table 4.2.2 ):
| Location | Area Class | Hazard | Fire Detection | Signaling |
|---|---|---|---|---|
| Residential Water Pump Station Wet Well | Div 2 or Unclassified | LEL (CH4 Flammable gases and floating flammable liquids | Audio/Visual Alarm, Locl/Remote | |
| Sewage Pumping Station Wel Well | Div 1 or Div 2 | LEL, H2S, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Odor Control Facility | Div 2 or Unclassified | LEL | Yes | Audio/ Visual Alarm, Locl/ Remote |
Solid Treatment Systems’ Locations (from NFPA 820 Table 6.2.2 ):
| Location | Area Class | Hazard | Fire Detection | Signaling |
|---|---|---|---|---|
| Scum-Handlung Building | Div 2 or Unclassified | LEL (CH4 Flammable gases and floating flammable liquids | Audio/ Visual Alarm, Locl/ Remote | |
| Scum Pits, Pumping Area | Div 1 or Div 2 | LEL | Audio/ Visual Alarm, Locl/ Remote | |
| Sludge Thinkener (Clarifier) | Div 1 or Div 2 | LEL, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Sludge Pumping Sation Dry Well | Div 2 or Unclassified | LEL, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Sludge Storage Wet Wells, Pits, Holding Tanks Area | Div 1 or Div 2 | LEL, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Sludge Blending Tanks and Holding Wells | Div 1 or Div 2 | LEL, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Anaerobic Digesters & Processing | Div 1 or Div 2 | LEL, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Underground (Piping) Tunnels | Div 1 or Div 2 | LEL | Yes | Audio/ Visual Alarm, Locl/ Remote |
What is required to have a gas detection system meet the requirement?
- Methane gas detectors shall be set to alarm at 10 percent of the lower explosive limit (LEL) in accordance with the manufacturer’s calibration instructions and shall be connected to alarm signaling systems. Oxygen and H2S detectors should be set per OSHA requirements
- Controller to monitor gas concentration and Ventilation
- Audio/Visual Alarm
Cost-Effective Solution from R.C. Systems - ZoneProtector
ZoneProtector is an integrated gas detection unit that meets NFPA 820 requirements. It has up to 4 channels to allow a combination of gas detection and ventilation monitoring signals. The sensors may be directly attached to the controller with a sampling pump unit to draw the gases from the detection points or mounted remotely at each detection point. One input channel can be used to monitor the ventilation system. The unit is equipped with audible/visual alarms and also provides configurable relays for remote alarms.Liquid Treatment Systems' Locations (from NFPA 820 Table 5.2.2 ):
| Location | Area Class | Hazard | Fire Detection | Signaling |
|---|---|---|---|---|
| Diverse Control | Div 1 or Div 2 | LEL (CH4 Flammable gases and floating flammable liquids | Audio/ Visual Alarm, Locl/ Remote | |
| Coarse and FIne Screen Facilites | Div 1 or Div 2 | LEL, H2S, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Flow Equalization Tanks Area | Div 1 or Div 2 | LEL | Audio/ Visual Alarm, Locl/ Remote | |
| Grit Removal Tanks Area | Div 1 or Div 2 | LEL, H2S, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Pre- Aeration Tanls Area | Div 1 or Div 2 | LEL, H2S, O2 | Audio/ Visual Alarm, Locl/ Remote | |
| Primary Sedimentation | Div 1 or Div 2 | LEL, H2S, O2 | Audio/ Visual Alarm, Locl/ Remote |
| Specifications | |
|---|---|
| Power Supply | 100-240VAC / 10-30VDC, 50W |
| Inputs | 4 Channel 4-20mA/DI |
| Standard Alarm Relays | 2x5 amp 30VDC or 250VAC resistive Form C |
| Optialam Alarm Relays | 6x 5 amp 30VDC or 250VAC resistive Form C |
| Analog Outputs (Optional) | 10 but 4-20mA outputs |
| Serial Port (Optional) | Modbus Master/ Slave RS- 485 port |
| Display | 128x64 pixel graphic LCD with backlight |
| 6x discrete LED | |
| Ambient Temperature | -35 to +60 degrees C |
| Approvals | CSA C22 No 1010.1 and C22.2 No 152 for combustibles and Isa S82.02; |
| UL 1604 / C22.2 No213 (NEMA 4x = Division 2 Groups A,B,C,D, | |
| En55011 adn EN61000 (CE Mark) |
Gas Detection Strategy 1: ZoneProtector With Sample Draw System:
Gas Detection Strategy 2: ZoneProtector With Remote Sensor
