To help public sector officials minimize fire and explosion hazards, the National Fire Protection Association (NFPA) publishes preventative requirements, fire codes and building standards. Used in alignment with state building codes, the NFPA 820 standard is specific to wastewater collection, transportation and treatment plants.
Methane generated by anaerobic biological activity in wastewater treatment presents a risk of fire-related accidents. Designing wastewater treatment plants and collection systems according to NFPA 820 guidelines can help mitigate this risk.
The National Electric Code (NFPA 70) defines classifications that correspond to the level of risk posed by explosive gases, combustible dust or ignitable fibers in an area. Wastewater systems typically deal with the potential for methane, an explosive gas, which falls into the Class 1 category under NFPA 820. The degree of hazard is further defined by Division 1 and Division 2 as described in the table below.
Fire hazard locations
Explosive or combustible gases posing as hazards are
|2. Class 1, Division 1 (C1D1)||
Explosive gases posing as hazards
|3. Class 1, Division 2 (C1D2)||
Explosive gases posing as hazards are not expected under normal operating conditions but
The hazardous classification defines requirements for electrical equipment, which may be installed. A variety of strategies may be used to make electrical devices suitable for use in a space with a hazardous classification. Most commonly, the devices will be either intrinsically safe to avoid providing an ignition source or will be explosion-proof to safely withstand the force of an explosion.
Measures must also be taken to ensure gases do not migrate through electrical conduits from a classified space into an unclassified space. These precautions result in greater costs for electrical installations within hazardous areas.
Some degree of risk in dealing with methane generated by wastewater processes is unavoidable. NFPA 820 establishes a standard for defining the degree of hazard by wastewater collection and treatment processes and standards for mitigating those risks. Some fundamental considerations in NFPA 820 include:
The first edition of NFPA 820 was released in 1990 with subsequent editions released in 1999, 2003, 2008, 2012, 2016 and most recently in 2020. Wastewater collection and treatment infrastructure has been in service for much longer.
Practices that once were considered sufficient to mitigate risks posed by potential methane generation are often not compliant with NFPA 820 standards. This is especially true of the following locations and processes:
Such spaces were often designed with no ventilation or intermittent ventilation, without sufficient separation from unclassified spaces such as electrical rooms, or without safety monitoring and alarming devices that meet NFPA 820 standards.