Wastewater treatment plants are essential structures in cities and small communities. Such facilities are closely monitored by several professional institutions, such as OSHA and the NFPA. When it comes to the latter group, guidelines set forth in NFPA 820 are regulations that dictate fire hazards in such facilities. Fire related accidents in wastewater treatment facilities are uncommon. However, when they do occur, they are often catastrophic in nature due to volatile conditions in the hazardous location.
NFPA 820 aims to address fire hazards in sludge (65 percent methane, 30 percent carbon dioxide and 5 percent other gases) and sewer (70 percent carbon dioxide, 25 percent other gases and 5 percent methane), which can easily be ignited via nearby electrical switches without explosion proof protection. These combustible gases can build up to dangerous concentration levels that can also lead to asphyxiation.
This article highlights key standards in NFPA 820 for wastewater treatment and collection facilities. The scope of this post includes lighting systems, electrical components, ventilation, construction materials and hazardous location classifications.
Explosion Proof, Corrosion Resistant and Vibration
There are several explosive compounds present in wastewater plants that are used for processing, power and cleaning. For example, chlorine and ammonia are applied to various treatment processes - when combined can turn explosive. Other risks include the saturation of methane and hydrogen sulfide in confined spaces (can cause asphyxiation and damage to olfactory nerves). Due to the presence of flammable, explosive gases and liquid-produced vapors, wastewater treatment facilities rely on Class I, Divisions 1 & 2 and Group D hazardous area lighting systems for illumination.
Class I, Division 1 refers to the following hazardous locations in the facility:
• Sanitary Sewer/Combined Sewer (Inside)
• Wastewater Pumping Station Wet Wells (Entire room)
• Above-grade Wastewater Pumping Station (Entire space)
• Maintenance Holes (Inside)
• Junction Chambers (Inside)
• Inverted Siphons
• Catch Basins
Class I, Division 2 refers to the following hazardous locations in the facility:
• Odor-control Areas
• Residential Diversion Structures
• Residential Below-grade Valve Vault
• Residential Control Structures
• Residential Below-grade Metering Vault
• Coarse and Fine-screen Facilities (within a 10-feet envelope around the equipment)
• Flow Equalization Tanks (within a 10-feet envelope around the equipment)
Furthermore, in sections of the building where corrosion can become an issue, luminaries with anti-corrosion properties may be deployed to prevent damage to the lighting system. This is strongly applicable to wastewater facilities in coastal regions that experience high temperatures, which can contribute to humidity and fast track corrosion. In such environments, it is vital to adhere to the maximum ambient temperature rating of the luminary to prevent inconsistent performance. Anti-corrosion lights are typically constructed of resilient materials, such as non-metallic surfaces, aluminum or stainless steel. Electro-static coatings (polyester or epoxy) may be applied to reinforce the lighting system’s anti-corrosion features.
Fixtures can be affected by strong vibrations caused by heavy machinery and large processing units. To minimize the effects of vibration, businesses must use mounting options that displace nearby rattling and light impacts. It would also be possible to use LEDs, due to their solid-state design, instead of metal halide units or fluorescent lamps. It is important to note that industry standards for mitigating vibration in wastewater treatment lights are non-existent.
Wastewater Treatment Lighting Systems
In application, NFPA 820 cites specific types of lights that must be installed in the building to ensure compliance. For ventilation system alarms, a dual light system may be used (composed of one “go” green light and one “no-go” red light) in place of an audible alarm. This is applicable to sections of the facility that are not constantly attended (NFPA 820 5-5.3). According to NFPA 820 A-5-5.3, warning devices should display a clear “Danger” sign to warn workers upon entry when an alarm condition is met.
Although luminaries are present in most sections of the establishment, NFPA 820 only mentions lighting systems a handful of times when defining specific sections of the facility (NFPA 1-5). In particular, dry wells, or part of a pumping station that offers isolation for pumping controls, is said to contain motors, fans, controls and lights. A wet well, or part of a pumping station that receives/stores wastewater, is also said to contain similar equipment.
The 2004 Edition of Recommended Standards for Wastewater Facilities, a set of policies that are used by 10 states (Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, New York, Ohio, Ontario, Pennsylvania and Wisconsin), elaborates further on the type of lighting systems that perform well in such infrastructural establishments. For example, luminaries in wet wells must be corrosion resistant and flexible cables should be reinforced with a watertight seal. To ensure electrical safety in pumping stations, an above-ground, fused disconnect switch must be provided with the main power feed (“Electrical Equipment” 42.35).
According to the document, no-shadow lighting should be available for reading dials, intricate measuring equipment, meniscuses and other measuring tools (“Lighting” 58.453). For waste gas burners, an auto-ignition mechanism in the form of a pilot light or photoelectric cell sensor unit must be present (“Pilot Light” 84.462). Lighting systems for nighttime operation and scheduled maintenance of tank car sites are emphasized in the guidelines (“Tank Cars” 102.33). Lastly, a labeled signal light that notifies nearby workers about fan operation should be installed at each entrance, in sections of the facility where multiple fan control points are available (“Electrical Controls” 102.55).
Lighting System Case Studies
The rise of LEDs has caused wastewater treatment facilities to switch from lighting systems composed of metal halide and fluorescent lamps to LEDs. In a case study that focused on replacing high-pressure sodium lights with LEDs at the City of Durham’s South Durham Wastewater Facility, the establishment was able to reduce energy consumption by up to 64 percent. The lighting system’s components included 20 high bay luminaries with 4000K- 5700K color temperature ratings and 70 CRI (mounted on poles).
Lastly, in a similar project at a Puerto Rico-based wastewater treatment plant, the facility was able to benefit from up to 75 percent in energy savings while improving illumination by replacing 16 250-watt high-pressure sodium lights with 100-watt LEDs. This resulted in over $3,500 in annual savings.