Wastewater treatment plants are prone to explosive risks due to the presence of volatile, flammable compounds inside the building. The Occupational Safety and Health Administration (OSHA) has highlighted the dangers of such hazardous environments through a federal safety investigation of a Canastota wastewater plant.
In 2014, a worker died from third-degree burns after a devastating explosion inside the facility. The employee was welding a pipe inside a methane gas dome at the treatment plant. OSHA representatives explained that the company failed to implement detectors inside the chamber during the incident. Open ventilation and emergency exits in the confined space were also lacking, which were cited in the incident report.
Explosive Compounds and UV Treatment
Wastewater facilities work with hazardous chemicals to treat and process large amounts of liquids. Chlorine and ammonia are examples of chemicals used to treat water. It is important to consider that both components on their own are not flammable. But when combined, the two substances can form explosive compounds. Furthermore, chlorine is easily mixed and absorbed by everyday materials, greatly increasing the possibility of creating flammable hazards. This characteristic also makes it difficult to detect in storage tanks, where concentrated amounts of the substance are present.
Dangerous gases from external sources, such as sewers and aeration tanks, should also be well accounted for in wastewater treatment plants. Such gases include methane, hydrogen sulphide and carbon monoxide. In particular, methane is not only flammable, but because of its ability to displace oxygen, it can easily cause asphyxiation in workers who are continuously exposed to the gas. Hydrogen sulphide becomes problematic when concentrated amounts are present, because at 150ppm or higher, the compound is almost impossible to discern without gas detectors. Low concentrations of the gas at 0.0047ppm emits a detectable odor, but as levels increase, it can damage olfactory nerves (receptors found in the nasal cavity), which reduces a worker’s ability to smell out the gas.
In order to lower risks related to igniting flammable compounds inside the facility, operators have been known to deploy gas detection devices in confined spaces. But such protocols only go as far as monitoring the hazardous area, and cannot actively prevent an explosion from taking place. Another tactic used by modern wastewater facilities is UV disinfection machines. This option is effective in replacing flammable chemicals used to treat water. The application of UVC bands (wavelengths between 200-280nm) deactivates harmful bacteria and viruses in the germicidal range. Examples of bacteria that succumb to UVC includes molds, E. coli, Salmonella, as well as Cryptosporidium and Giardia (chlorine-resistant protozoa).
Hazardous Area Lighting (Class I, Div 2)
Using UV light to disinfect water is not a comprehensive solution, when it comes to preventing the combustion of volatile chemicals. This is because some explosive compounds present in the facility have nothing to do with actual wastewater processing. For example, flammable biogas from sludge digestion is mainly used to generate electricity for the building. An unforeseen leak in the machine could result in fatal explosions, should the gas react with sparks generated by electronics around the area.
To prevent such occurrences, wastewater companies may install hazardous area lighting with Class 1 Division 2 (C1D2) approval ratings. According to the National Electric Code (Article 501) C1D2 refers to hazardous locations where volatile flammable gases, liquid-produced vapors or combustible liquid-produced vapors are used, processed or handled. This includes confined spaces, closed systems and locations without adequate ventilation. The explosion proof luminaries work by preventing the creation of spark and explosions from escaping the fixture, where it can react (or possibly ignite) with flammable compounds.
LED Case Study
Traditionally, wastewater plants use a combination of metal halide and mercury vapor lamps for their lighting needs. The high-intensity discharge fixtures are inefficient and costly to maintain when used for long periods of time in demanding environments. This has led to the prolific adoption of LEDs, as a more robust, energy efficient and powerful lighting solution for processing plants in the sector. A case study that displays the advantages of LEDs in wastewater facilities comes from the city of Santa Cruz, California. A wastewater plant located in the city that processes over 10 million gallons of water on a daily basis has successfully replaced its high-pressure sodium and mercury vapor lights with LEDs.
The switch, which took around five days to complete, allowed the plant to reduce its annual lighting costs by up to 50 percent. Additionally, the business will get its investment back after three years of operation. During the project, lighting specialists replaced a total of 82 outdated units with 33 low bay LEDs and 49 high bay LEDs.